Java: Guide: Java Essentials

Java Essentials 2013

Java Language

Main Class

public static void main(String[] args) {

Required by Class:

public - can be called anywhere
static - no instance required to run
void - nothing returned by class
String[] args

[] - an array
args - default variable to hold passed data
Passed by Java’s JVM

Passing Args

Command Line

java Main arg1 arg2

In Eclipse:

Documentation

http://docs.oracle.com/javase/6/docs/api/
Mouseover, F2
Windows > View > Help

Garbage Collection

Objects referenced created in heap memory
As long as variable referenced, it’s retained
When referenced expire, they’re eligible to be garbage collected
Garbage Collector runs own thread
Can’t force garbage collection
OutOfMemoryError thrown if memory runs out

Expiration

Variable to local functions or blocks expire when function is complete
Set value to null

Tips for Managing Memory

Minimize number of object created
Runtime.*

Runtime.maxMemory()
Runtime.totalMemory()
Runtime.freeMemory()

java -Xms256s HelloWorld - Initial heap size
java -Xms256m HelloWorld - Max heap size
java -Xms256n HelloWorld - Heap size for young generation objects

Classes and Objects

//Starting class has main() method

public class SimpleApplication {

        // 

        public static void main(String[] args) {

                // Welcomer = datatype

                // welcomer is new instance

                Welcomer welcomer = new Welcomer();

                welcomer.sayHello();

        }

}


public class Welcomer {

// instance variable = welcome - private to the class

private String welcome = “Hello”;

        public void sayHello() {

                System.out.println(welcome);

        }

}

String variables objects

String is class

String welcome = “Hello!”;

String welcome = new String(“Hello!”);

String = array[H,e,l,l,o,!]

Same as:

char[] chars = {‘H’,’e’,’l’,’l’,’o’,’!’};

String s = new String(chars);

Types of Variables

Primitives - stored directly in memory

Numerics - ints, floating point decimals
Single characters
Boolean (true/false)

Complex objects

Strings
Dates
Everything else

Declaring a Primitive Varialbe

Data Type - Required
Variable name - Required
Initial value - option

int newVariable = 10;
[Data type] [Variable name] = [Initial value];
variable name MUST start with lowercase
Numeric default = 0
Boolean default = false

Declaring a Complex Variable

instance of classes
declared in 3 parts
Init uses new keyword and class constructor
Inital value - optional, built from class constructor
Date newDate = new Date();
[Data type] [Variable name] = [Initial value from constructor]
Variable name alpha char or _
Date newDate = null

Scope

local vars - declared inside function (de-referenced)

void doSomething()

public vars -

public doSomethingElse()

Class variables = Field variable

Declared outside a class method

public class MyClass {

        String sayHello = new String(“Hello”);

        void doSomething() {

                System.out.println(sayHello);

        }

}

Numeric are Primitives

Simple value
Stored in fastest memory
Numeric/Boolean
all lowercase
int varprimitive

Type

Bits

Min

Max

byte

-128

127

short

-32,768

32,767

int

-2,147,483,648

2,147,483,647

long

-9.22337E+18

9.22337E+18

float

double

Setting Literal Values

byte b = 1;
short s = 10;
int i = 10;
long l = 100L;
float f = 150.5f;
double d = 150.5d;

Without extra char, Java will cast it automatically, not using memory most efficiently

Helper Classes

Data Type

Helper Class

byte

Byte

short

Short

int

Integer

long

Long

float

Float

double

Double

Numeric Wrapper Class

Double provides tools for convering float values
double doubleValue = 156.5d;
Double doubleObj = new Double(doubleValue);
byte myByteValue = boubleObj.byteValue();
int myIntValue = doubleObj.intValue();
float myFloatValue = doubleObj.floatValue();
Strig myString = double.Obj.toString();

BigDecimal

For currency values that have guaranteed precision

Problem

BigDecimal payment = new BigDecimal(1115.37);

System.out.println(payment.toString());

>1115.36999999908796...

...Result determined by OS, Processor, etc

Solution

double d = 1115.737;

String ds = Double.toString(d);

BigDecimal bd = new BigDecimal(ds);

System.out.println(“the value is “ + db.toString());

>Value is 1115.37

Converting Primitives Upward/Downward

Converting upwards:

int intvalue = 120;
double doubleResult = intValue; // = 120.0 (double)

Converting downwards:

double doublevalue = 3.99;

int intResult = doubleValue; // won’t even compile due to accuracy loss

int intResult = (int)doubleValue; // explicit accuracy loss by truncating

= 3

double
float
long
int
short
byte

Wrapping Around when converting Downward

double > byte

int i = 128;

byte b = (byte)i;

> -128

Casting Syntax VS Helper Class

Casting

Doesn’t add another object to memory
Can’t use afterwards

double doubleValue = 3.99;

int intResult = (int)doubleValue;

Helper Class

Creates instance of Helper Class in memory
Good when needing to do things with it later

double doubleValue = 3.99;

double doubleObj = new Double(doubleValue);

int intResult = doubleObj.intValue();

Operators

follows C standards

Types

Assignment
Equality or relational
Mathematical
Conditiona
Ternary (short-hand conditional)

Assignment and Math Operators

=, +, -, *, /, %

Incrementing

intValue = 10;

intValue ++; // 11

intValue --; // 9

intValue += 5; // 15

intValue -= 5; // 5

intValue *= 5; // 25

intValue /= 5; // 2

PostFix vs Prefix Incrementing

int intValue = 10;

PostFix

Do operator, then evaluate

System.out.println(intValue ++)

output = 10

new value = 11

Prefix (a.k.a.) Unerary

Evaluate, then do operator

System.out.println(+ intValue);

output = 11

new value = 11

Comparing Values

>, <, >=, <=, instanceof (Class Membership)

String s = “Hello”;

if (s instanceof java.lang.String) {

        System.out.println(“s is a String”);

}

Comparing Strings

String s1 = “Hello”;

String s2 = “Hello”;

if (s1 == s2) {

        System.out.println(“They Match!);

} else {

        System.out.println(“No Match!);

}

> No Match!


if (s1.equals(s2)) {

        System.out.println(“They Match!);

} else {

        System.out.println(“No Match!);

}

>They Match!

Equality Operators

== Equality

!= IInequality

if(!this) Reversing logic: booleans only

Conditional Operators

&& AND

|| OR

Characters

Code:

public static void main(String[] args) {

char c1 = '1';

char c2 = '2';

char c3 = '3';

//unicode

char dollar = '\u0024';

System.out.print(dollar);

System.out.print(c1);

System.out.print(c2);

System.out.println(c3);

//Wrapper Class: Character

char a1 = 'a';

char a2 = 'b';

char a3 = 'c';

System.out.print(Character.toUpperCase(a1));

System.out.print(Character.toUpperCase(a2));

System.out.println(Character.toUpperCase(a3));

}

Booleans

Code:

        public static void main(String[] args) {

           boolean b1 = true;

           boolean b2 = false;

           

           System.out.println("The value of b1 is " + b1);

           //true

           

           System.out.println("The value of b2 is " + b2);

           //false

           

           boolean b3 = !b1;

           System.out.println("The value of b3 is " + b3);

           // false

           

           int i = 0; //NOT true in java

           boolean b4 = (i != 0); //translate int to boolean

           System.out.println("The value of b4 is " + b4);

           //false


           String s1 = "true"; // or TRUE

           boolean b5 = Boolean.parseBoolean(s1);

           System.out.println("The value of b5 is " + b5);

           // true

           

           String s2 = "FALSE"; // or false

           boolean b6 = Boolean.parseBoolean(s2);

           System.out.println("The value of b6 is " + b6);

           // false

           

           String s3 = "BLAH"; // =  false

           boolean b7 = Boolean.parseBoolean(s3);

           System.out.println("The value of b7 is " + b7);

           //false

   }

StringOutput

Code:

public class Main {


   public static void main(String[] args) {

           char c = 'z';

           boolean bool = true;

           byte b = 127;

           short s = 32000;

           int i = 2000000;

           long l = 10000000L;

           float f = 1234245.435234f;

           double d = 112312312331.34;

           

           System.out.println(c);

           System.out.println(bool);

           System.out.println(b);

           System.out.println(s);

           System.out.println(i);

           System.out.println(l);

           System.out.println(f);

           System.out.println(d);  

/*

32000

2000000

10000000

1234245.4

1.1231231233134E11

*/

           // first value in the print Math or String

           System.out.println("The value of s is " + s);

           //The value of s is 32000

           

           // if one String is involved, whole thing is string

           System.out.println(s + " The value of s is ");

           //32000 The value of s is

           

           // math converted first, then tacked onto string

           // String first, no math...all string


           // needs 'Date' package

           Date myDate = new Date();

           System.out.println("The new date is " + myDate);

           //The new date is Fri Aug 03 14:55:55 CDT 2012            

   }


}

Calculator

Code:

import java.io.*;


public class Calculator {


   public static void main(String[] args) {

           String s1 = getInput("Enter a numeric value: ");

           String s2 = getInput("Enter a numeric value: ");

           

           double d1 = Double.parseDouble(s1);

           double d2 = Double.parseDouble(s2);

           double result = d1 + d2;

           System.out.println("The answer is " + result);

//Enter a numeric value: 10

//Enter a numeric value: 25.5

//The answer is 35.5


/*

Enter a numeric value: xyz

Enter a numeric value: abc

Exception in thread "main" java.lang.NumberFormatException: For input string: "xyz"

   at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)

   at java.lang.Double.parseDouble(Unknown Source)

   at Calculator.main(Calculator.java:9)

*/

           

   }

   

   private static String getInput(String prompt) {

           BufferedReader stdin = new BufferedReader(

                           new InputStreamReader(System.in));


           System.out.print(prompt);

           System.out.flush();

           

           try {

                   return stdin.readLine();

           } catch (Exception e) {

                   return "Error: " + e.getMessage();

           }

   }


}

CompareStrings

Code:

public class Main {


   public static void main(String[] args) {

           int monthNumber = 7;

           

           if (monthNumber >= 1 && monthNumber <=3) {

                   System.out.println("You're in Quarter 1");

           }    

           else if (monthNumber >= 4 && monthNumber <=6) {

                   System.out.println("You're in Quarter 2");

           }

           else {

                   System.out.println("You're not in the first half of the year!");

           }

   }

}


public class CompareStrings {


   public static void main(String[] args) {

           String month = "February";

           

           if (month.equals("February")) {

                   System.out.println("It's the second month!");

           }


   }


}

Switch Statements: Integers

Code:

import java.io.BufferedReader;

import java.io.InputStreamReader;


public class SwitchWithInts {


   public static void main(String[] args) {

           String input = getInput("Enter a number between 1 and 12: ");

           int month = Integer.parseInt(input);

           

           switch (month) {

           case 1:

                   System.out.println("The month is January");

                   break; //must use break to leave switch

           case 2:

                   System.out.println("The month is February");

                   break;

           case 3:

                   System.out.println("The month is March");

                   break;

           default:

                   break;

           }

   }

   

   private static String getInput(String prompt) {

           BufferedReader stdin = new BufferedReader(

                           new InputStreamReader(System.in));


           System.out.print(prompt);

           System.out.flush();

           

           try {

                   return stdin.readLine();

           } catch (Exception e) {

                   return "Error: " + e.getMessage();

           }

   }


}

Switch Statements: Enums

Project > New > Enum

Code:

public enum Month {

   JANUARY, FEBRUARY, MARCH; //Constants of enum class

}



public class SwitchWithEnums {

   // Enumerations

   public static void main(String[] args) {


//            int month = 1;

           Month month = Month.FEBRUARY;

           

           switch(month) {

           case JANUARY:

                   System.out.println("It's the first month");

                   break;

           case FEBRUARY:

                   System.out.println("It's the second month");

                   break;

           case MARCH:

                   System.out.println("Its the third month");

           }


   }


}

Switch Statements: Strings (Java SE7)

Loops

Code:

public class Main {


   static private String[] months =

           {"January", "February", "March",

           "April", "May", "June",

           "July", "August", "September",

           "October", "November", "December"};


   public static void main(String[] args) {


           // using counter variables instead of complex objects

//            for (int i = 0; i < months.length; i++) {

//                    System.out.println(months[i]);                    

//            }


           // For each month in the months[] array

//            for (String month : months) {

//                    System.out.println(month);

//            }


           // eval BEFORE loop

//            int counter = 0;

//            while (counter < months.length) {

//                    System.out.println(months[counter]);

//                    counter ++;

//            }


           // eval AFTER loop

           int counter = 0;

           do {

                   System.out.println(months[counter]);

                   counter ++;

           } while (counter < months.length);

   }

}

Methods

Refactoring

Code:

public class Main {

public static void main(String[] args) {

doSomething();

//refactoring, copy code, Refactor..

//will create a new method and reference it here

loopMe();

}

private static void loopMe() {

int top = 10;

for (int i = 0; i < top; i++) {

System.out.println("the value is " + i);

}

//Access modifier public, private, protected (inheritance), none (protected package)

//Static - class method, only used inside class

//non-Static - used in instances

//Static must create instance to call non-Static '.method()'

private static void doSomething() {

System.out.println("This method has been called");

}

Extracting a Method

Code:

import java.io.*;

public class Calculator {

public static void main(String[] args) {

String s1 = getInput("Enter a numeric value: ");

String s2 = getInput("Enter a numeric value: ");

// Extracting a Method

double result = addTwovValues(s1, s2);

System.out.println("The answer is " + result);

}

// Extracted Method

private static double addTwovValues(String s1, String s2) {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 + d2;

return result;

}

private static String getInput(String prompt) {

BufferedReader stdin = new BufferedReader(

new InputStreamReader(System.in));

System.out.print(prompt);

System.out.flush();

try {

return stdin.readLine();

} catch (Exception e) {

return "Error: " + e.getMessage();

}

Method Overloading (Multiple methods with same name/diff args)

Code:

public class Main {

public static void main(String[] args) {

int value1 = 5;

int value2 = 10;

int value3 = 15;

int result = addValues(value1, value2, value3);

System.out.println("The result is: " + result);

String string1 = "10";

String string2 = "25";

int result2 = addValues(string1, string2);

System.out.println("The result is: " + result2);

}

private static int addValues(int int1, int int2){

return int1 + int2;

}

// will handle call if 3 values passed

private static int addValues(int int1, int int2, int int3){

return int1 + int2 + int3;

}

// handle different data types

private static int addValues(String val1, String val2){

int value1 = Integer.parseInt(val1);

int value2 = Integer.parseInt(val2);

return value1 + value2;

}

Passing By Copy; Primitives

When calling a function, a COPY of the argument is passed to the method

void incrementValue(int inFunction) {

inFunction ++;

System.out.println("In function: " + inFunction);

}

int original = 10;

System.out.println("Original before : " + original);

incrementValue(original);

System.out.println("Original after : " + original);

// Original before: 10

// In function: 11

// Original after: 10

}

Passing by Reference: Complex Objects

Variable of Complex Object is a Reference to Memory
A Copy of the Complex Object is passed, but references the same memory addresses

inf[] original = {10,20,30};

original[0] > {10,20,30} < inFunction[0]

Passing Strings: Is Complex Object but Acts Like Primitive

void changeString(String inFunction) {

inFunction = “New!”;

System.out.println(“In function: “ + inFunction);

}

Strings are immutable, can’t change after declaration
Copy of entire string passed to function

// Original before: Original!

// In function: New!

// Original after: Original!

Extract Method with Error Handling

More Complex Programs and An Error Handling Declaration

Code:

import java.io.*;

public class Calculator2 {

public static void main(String[] args) {

String s1 = getInput("Enter a numeric value: ");

String s2 = getInput("Enter a numeric value: ");

String op = getInput("Enter 1=Add, 2=Subtract, 3=Multiply, 4=Divide: ");

int opInt = Integer.parseInt(op);

// declare variables BEFORE switch

double result = 0;

switch (opInt) {

case 1:

result = addValues(s1, s2);

break;

case 2:

result = subtractValues(s1, s2);

break;

case 3:

result = multiplyValues(s1, s2);

break;

case 4:

result = divideValues(s1, s2);

break;

default:

System.out.println("Unknown Operation: " + op);

break;

}

System.out.println("The answer is " + result);

}

private static double divideValues(String s1, String s2) {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 / d2;

return result;

}

private static double multiplyValues(String s1, String s2) {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 * d2;

return result;

}

private static double subtractValues(String s1, String s2) {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 - d2;

return result;

}

private static double addValues(String s1, String s2)

throws NumberFormatException {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 + d2;

return result;

}

private static String getInput(String prompt) {

BufferedReader stdin = new BufferedReader(

new InputStreamReader(System.in));

System.out.print(prompt);

System.out.flush();

try {

return stdin.readLine();

} catch (Exception e) {

return "Error: " + e.getMessage();

}

Using Equality Operators

Code:

public class Main {

public static void main(String[] args) {

String s1 = ("Welcome to California");

String s2 = new String("Welcome to California");

System.out.println(s2);

if (s1 == s2) { //comparing OBJECTS not VALUES

System.out.println("With == They match");

}

else {

System.out.println("With == No match");

}

if (s1.equals(s2)) { //case sensitive

System.out.println("With .equals() They match");

} else {

System.out.println("With .equals() No match");

}

// Prints string out one char at a time

char[] chars = s1.toCharArray();

for (char c : chars) {

System.out.println(c);

}

String Builder vs String Buffer

Builder - single thread
Buffer - multi threaded

Code:

public class Main {

public static void main(String[] args) {

String s1 = "Welcome";

StringBuilder sb = new StringBuilder(s1);

sb.append(" to California");

System.out.println(sb);

//string builder vs string buffer

}

String Manipulation

Code:

public class Main {

public static void main(String[] args) {

String s1 = ("Welcome to California!");

System.out.println("Length of string: " + s1.length());

//String position

int pos = s1.indexOf("California");

System.out.println("Position of California: " + pos);

// SubStrings

String sub = s1.substring(11);

System.out.println(sub);

String s2 = "Welcome! ";

int len1 = s2.length();

System.out.println(len1);

String s3 = s2.trim();

System.out.println(s3.length());

}

Date Manipulation

Code:

import java.text.DateFormat;

import java.util.Date;

import java.util.GregorianCalendar;

public class Main {

public static void main(String[] args) {

Date d = new Date();

System.out.println(d);

//Fri Aug 03 17:43:06 CDT 2012

//Date class that can add days to, etc

GregorianCalendar gc = new GregorianCalendar(2009, 1, 28);

System.out.println(gc);

//java.util.GregorianCalendar[time=1235887200000,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="America/Chicago",offset=-21600000,dstSavings=3600000,useDaylight=true,transitions=235,lastRule=java.util.SimpleTimeZone[id=America/Chicago,offset=-21600000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2009,MONTH=2,WEEK_OF_YEAR=10,WEEK_OF_MONTH=1,DAY_OF_MONTH=1,DAY_OF_YEAR=60,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=1,AM_PM=0,HOUR=0,HOUR_OF_DAY=0,MINUTE=0,SECOND=0,MILLISECOND=0,ZONE_OFFSET=-21600000,DST_OFFSET=0]

//need to prep for printing....

//add gc field (YEAR/MONTH/DATE), add by how much

gc.add(GregorianCalendar.DATE, 1);

//prep for printing

Date d2 = gc.getTime();

System.out.println(d2);

//Sun Mar 01 00:00:00 CST 2009

//factoring method, returns an instance of that class

DateFormat df = DateFormat.getDateInstance();

String sd = df.format(d2);

System.out.println(sd);

//Mar 1, 2009

// can format the Date object in many ways..

DateFormat df2 = DateFormat.getDateInstance(DateFormat.FULL);

String sd2 = df2.format(d2);

System.out.println(sd2);

//Sunday, March 1, 2009

}

Error Handling

Code:

public class Main {

public static void main(String[] args) {

//declarations

//String s;...need to assign value

String s = null;

System.out.println(s);

//Arrays

String[] strings = {"Welcome!"}; //one item in array

System.out.println(strings[1]); // error, no [1], only [0]

//Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1

//at Main.main(Main.java:13)

}

Exception Handling

Code:

public class Main {

public static void main(String[] args) {

//try catch block

try {

String[] strings = {"Welcome!"};

System.out.println(strings[1]);

} catch (ArrayIndexOutOfBoundsException e) {

//e.printStackTrace();

System.out.println("Error occurred");

}

// without try/catch block

// Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1

// at Main.main(Main.java:6)

//with try/catch blcok

//The application is still running!

//java.lang.ArrayIndexOutOfBoundsException: 1

//at Main.main(Main.java:9)

//with error handling

//Error occurred

//The application is still running!

System.out.println("The application is still running!");

}

Extracting and Error Handling with Try/Catch Block: Revisited

String[] strings = {"Welcome!"};

System.out.println(strings[1]);

getArrayItem(); //refactored getArrayItem()

private static void getArrayItem()

throws ArrayIndexOutOfBoundsException {

String[] strings = {"Welcome!"};

System.out.println(strings[1]);

}

try {

getArrayItem(); //refactored getArrayItem()

} catch (ArrayIndexOutOfBoundsException e) {

// e.printStackTrace(); // <--- throws ugly message

System.out.println("Array item was out of bounds");

}

Code:

public class Main {

public static void main(String[] args) {

//Extrac Method with Error Handling

//Surround with try/catch blcok

try {

getArrayItem(); //refactored getArrayItem()

} catch (ArrayIndexOutOfBoundsException e) {

// e.printStackTrace(); // <--- throws ugly message

System.out.println("Array item was out of bounds");

//Array item was out of bounds

}

private static void getArrayItem()

throws ArrayIndexOutOfBoundsException {

String[] strings = {"Welcome!"};

System.out.println(strings[1]);

}

Debugger

Finding Possible Exceptions

Highlight command > Help > Dynamic Help > JavaDoc > CONSTRUCTOR > METHOD

URI uri = new URI("http:\\somecompany.com");

java.net.URISyntaxException: Illegal character in opaque part at index 5: http:\somecompany.com

at java.net.URI$Parser.fail(Unknown Source)

at java.net.URI$Parser.checkChars(Unknown Source)

at java.net.URI$Parser.parse(Unknown Source)

at java.net.URI.<init>(Unknown Source)

at Main.main(Main.java:10)

From e.printStackTrace();

To System.out.println(e.getMessage());

Code:

import java.net.URI;

import java.net.URISyntaxException;

public class Main {

public static void main(String[] args) {

//Uniform Resource Identifier

try {

URI uri = new URI("http:\\somecompany.com");

} catch (URISyntaxException e) {

System.out.println(e.getMessage());

e.printStackTrace();

java.net.URISyntaxException: Illegal character in opaque part at index 5: http:\somecompany.com

at java.net.URI$Parser.fail(Unknown Source)

at java.net.URI$Parser.checkChars(Unknown Source)

at java.net.URI$Parser.parse(Unknown Source)

at java.net.URI.<init>(Unknown Source)

at Main.main(Main.java:10)

}

System.out.println("I'm alive!");

//Exception in thread "main" java.lang.Error: Unresolved compilation problem:

// Unhandled exception type URISyntaxException

// at Main.main(Main.java:8)

}

Simple Arrays

Arrays NOT resizeable at runtime..

Code:

public class Main {

public static void main(String[] args) {

int[] a1 = new int[3]; //array of 3 integers

for (int i = 0; i < a1.length; i++) {

System.out.println(a1[i]);

}

int a2[] = new int[3]; //array of 3 integers

for (int i = 0; i < a2.length; i++) {

System.out.println(a2[i]);

}

int[] a3 = {3,6,9};

for (int i = 0; i < a3.length; i++) {

System.out.println(a3[i]);

}

System.out.println("The value of the first item is: " + a3[0]);

}

2 Dimensional Arrays

Code:

public class Main {

public static void main(String[] args) {

String[][] states = new String[3][2];

states[0][0] = "California";

states[0][1] = "Sacramento";

states[1][0] = "Oregon";

states[1][1] = "Salem";

states[2][0] = "Washington";

states[2][1] = "Olympia";

for (int i = 0; i < states.length; i++) {

StringBuilder sb = new StringBuilder();

for (int j = 0; j < states[i].length; j++) {

if (j == 0) {

sb.append("The Capitol of ");

} else {

sb.append(" is ");

}

sb.append(states[i][j]);

}

System.out.println(sb);

}

MultiDimensional Arrays

Code:

import java.util.ArrayList;

public class Main {

public static void main(String[] args) {

//Diamond Operator <E> = Specific DataType

ArrayList<String> list = new ArrayList<String>();

list.add("California");

list.add("Oregon");

list.add("Washington");

System.out.println(list);

// Allows changing array size at runtime

list.add("Alaska");

System.out.println(list);

list.remove(0);

System.out.println(list);

String state = list.get(1);

System.out.println("The second state is " + state);

int pos = list.indexOf("Alaska");

System.out.println("Alaska is at position " + pos);

Boolean b = list.contains("California");

System.out.println(b);

b = list.contains("Alaska");

System.out.println(b);

}

HashMap: Unordered data collections

Code:

import java.util.HashMap;

// HashMap is for storing unordered data collections

public class Main {

public static void main(String[] args) {

// <these are> generics

HashMap<String, String> map = new HashMap<String, String>();

map.put("California", "Sacramento");

map.put("Oregon", "Salem");

map.put("Washington", "Olympia");

System.out.println(map);

//{California=Sacramento, Oregon=Salem, Washington=Olympia}

map.put("Alaska", "Juneau");

System.out.println(map);

//{California=Sacramento, Oregon=Salem, Washington=Olympia, Alaska=Juneau}

String cap = map.get("Oregon");

System.out.println("The capitol of Oregon is " + cap);

//The capitol of Oregon is Salem

map.remove("California");

System.out.println(map);

//{Oregon=Salem, Washington=Olympia, Alaska=Juneau}

}

Encapsulation

Encapsulate functions by wrapping sections of code in a class/method
Now reuseable
Changing in one place, not many

Code:

Classes

Class = Filename.java
Only one public class per java file
Multiple classes only accessible within the files
Refactoring is process of pulling code out, creating method/class

Also changing class name is refactoring

Code:

From

result = divideValues(s1, s2);

To

result = SimpleMath.divideValues(s1, s2);

From

----------------------------------------------------------

public class Calculator2 {

private static double divideValues(String s1, String s2) {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 / d2;

return result;

----------------------------------------------------------

To

----------------------------------------------------------

public class SimpleMath {

public static void main(String[] args) {

}

public static double divideValues(String s1, String s2) {

double d1 = Double.parseDouble(s1);

double d2 = Double.parseDouble(s2);

double result = d1 / d2;

return result;

----------------------------------------------------------

Packages

If class is anywhere but default package, it must be declared
when creating packages, use reverse domain...

com.silosix.calc

Importing Packages

package com.lynda.calc;

import com.lynda.calc.helpers.InputHelper;

import com.lynda.calc.helpers.MathHelper;

same as:

package com.lynda.calc;

import com.lynda.calc.helpers.*;

CTRL-O will change * to specific class imports

Refactor > Move

Instance Methods

Class method called from definition of the class

building up utility functions that pass all data in the call
STATIC present

Instance method call from instance of the class - OBJECT

objects stick around and retain their data so its always accessible.
STATIC missing

Method declarations

static - class method
public - called anywher ein ap
private - only within class
protected - only within this class or its subclasses

Object Superclass methods with
Olive()’s crush() method
Olive inherits Object() methods/properties

Code: Main.java

package com.lynda.olivepress;

import com.lynda.olivepress.olives.Olive;

import com.lynda.olivepress.press.OlivePress;

public class Main {

public static void main(String[] args) {

//creating 3 anonymous Olive objects

Olive[] olives = {new Olive(), new Olive(), new Olive()};

OlivePress press = new OlivePress();

press.getOil(olives);

}

Code: OlivePress.java

package com.lynda.olivepress.press;

import com.lynda.olivepress.olives.Olive;

public class OlivePress {

public void getOil(Olive[] olives) {

for (Olive olive : olives) {

olive.crush();

}

Code: Olive.java

package com.lynda.olivepress.olives;

public class Olive {

public void crush() {

System.out.println("Ouch!");

}

Instance Variables (Not Static)

Constructors

Constructors have no return value (void, int, etc)
can create multiple constructors (overloading) with different input specs
Always create a ‘no argument’ constructor for clarity

public OlivePress() { }

Can Create a new constructor with fields....

Constructor of the Olive() class

public Olive() {

System.out.println("Constructor of " + this.name);

}

Creating another constructor to catch argument and populate a field:

public Olive(int oil) {

//this.oil means field(instance variable

//otherwise refers to argument

this.oil = oil;

}

Code:

package com.lynda.olivepress.olives;

public class Olive {

public String name = "Kalamata";

public String flavor = "Grassy";

public long color = 0x000000;

private int oil = 3;

//constructor, same name as class

//no return on constructors

//can overload the constructor

public Olive() {

System.out.println("Constructor of " + this.name);

}

public Olive(int oil) {

this.oil = oil;

}

public int crush() {

System.out.println("ouch!");

return oil;

}

Getters/Setters

OO development patters
Fields should be private
Get to data with get/set

Create private get() and set()

Eclipse can create get/set code via Source:

Creates:

public int getOil() {

return oil;

}

public void setOil(int oil) {

this.oil = oil;

}

Code: Main.java

package com.lynda.olivepress;

import java.util.ArrayList;

import com.lynda.olivepress.olives.Olive;

import com.lynda.olivepress.press.OlivePress;

public class Main {

public static void main(String[] args) {

ArrayList<Olive> olives = new ArrayList<Olive>();

Olive olive;

olive = new Olive(2);

System.out.println(olive.name);

olives.add(olive);

olive = new Olive(1);

System.out.println(olive.name);

olives.add(olive);

olive = new Olive(2);

System.out.println(olive.name);

olives.add(olive);

OlivePress press = new OlivePress();

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() + " units of oil");

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() + " units of oil");

}

Code: OlivePress.java

package com.lynda.olivepress;

import java.util.ArrayList;

import com.lynda.olivepress.olives.Olive;

import com.lynda.olivepress.press.OlivePress;

public class Main {

public static void main(String[] args) {

ArrayList<Olive> olives = new ArrayList<Olive>();

Olive olive;

olive = new Olive(2);

System.out.println(olive.name);

olives.add(olive);

olive = new Olive(1);

System.out.println(olive.name);

olives.add(olive);

olive = new Olive(2);

System.out.println(olive.name);

olives.add(olive);

OlivePress press = new OlivePress();

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() + " units of oil");

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() + " units of oil");

}

Code: Olive.java

package com.lynda.olivepress;

import java.util.ArrayList;

import com.lynda.olivepress.olives.Olive;

import com.lynda.olivepress.press.OlivePress;

public class Main {

public static void main(String[] args) {

ArrayList<Olive> olives = new ArrayList<Olive>();

Olive olive;

olive = new Olive(2);

System.out.println(olive.name);

olives.add(olive);

olive = new Olive(1);

System.out.println(olive.name);

olives.add(olive);

olive = new Olive(2);

System.out.println(olive.name);

olives.add(olive);

OlivePress press = new OlivePress();

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() + " units of oil");

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() + " units of oil");

}

Class Variables

Java has no CONSTANT declaration so......

// public - accessible from entire app

// static - class var

// final - value can't be changed

IN Olive()...

public static final long BLACK= 0x000000;

using it

public long color = Olive.BLACK;

Inheritance

Java has only single inheritance - only one inherited parent
Parent/child
Base/derived
Superclass/subclass <- Preferred Java nomenclature

By default Object() is the superclass unless directly specified

Polymorphism

Can used as Superclass or Subclass
Declare the object by Superclass

Superclass can have more than one subclass

Private - only called within own class
Protected - called by own class or subclass
Public - called from anywhere

Subclasses extend superclass

extending Olive by setting inital volume (setVolume)

public class Kalamata extends Olive() {

public Kalamata() {this.setVolume(2);}

}

public class Liguria extends Olive() {

public Liguria () {this.setVolume(5);}

}

…..this creates inheritance

Olive[] olives = {new Kalamata(), new Liguria(), new Kalamata()};

OlivePress press = new OlivePress(olives);

OliveOil oil - press.getOil;

Takes Kalamata() class and fits into Superclass Olive()

Extending Custom Classes

Superclass doesnot pass on its constructor so...
Each subclass needs its own constructor

In subclass... use IDE to copy constructors from the Superclass

Can select all or one...

Superclass Olive() has two constructor methods (its overloaded)

Creates...

public Kalamata() {

super();//calling superclass constructor method

// TODO Auto-generated constructor stub

}

Code: Main

package com.lynda.olivepress;

import java.util.ArrayList;

import com.lynda.olivepress.olives.Kalamata;

import com.lynda.olivepress.olives.Ligurian;

import com.lynda.olivepress.olives.Olive;

import com.lynda.olivepress.press.OlivePress;

public class Main {

public static void main(String[] args) {

ArrayList<Olive> olives = new ArrayList<Olive>();

Olive olive;

//olive = new Olive(2); //Was calling SuperClass

olive = new Kalamata();

System.out.println(olive.name);

olives.add(olive);

olive = new Ligurian();

System.out.println(olive.name);

olives.add(olive);

olive = new Kalamata();

System.out.println(olive.name);

olives.add(olive);

OlivePress press = new OlivePress();

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() +

" units of oil");

press.getOil(olives);

System.out.println("You got " + press.getTotalOil() +

" units of oil");

}

Code:Olive.java

package com.lynda.olivepress.olives;

public class Olive {

public static final long BLACK = 0x000000;

public static final long GREEN = 0x00ff00;

public String name = "Kalamata";

public String flavor = "Grassy";

public long color = Olive.BLACK;

private int oil = 3;

public int getOil() {

return oil;

}

public void setOil(int oil) {

this.oil = oil;

}

public Olive() {

System.out.println("Constructor of " + this.name);

}

public Olive(int oil) {

setOil(oil);

}

public int crush() {

System.out.println("ouch!");

return oil;

}

Code:Kalamata

package com.lynda.olivepress.olives;

public class Kalamata extends Olive {

public Kalamata() {

super(2); //calling superclass constructor method and passing '2'

this.name = "Kalamata";

this.flavor = "Grassy";

this.color = Olive.BLACK;

}

Overriding Methods (super.something();)

Code: Olive.java

package com.lynda.olivepress.olives;

public class Olive {

public static final long BLACK = 0x000000;

public static final long GREEN = 0x00FF00;

public String name = "Kalamata";

public String flavor = "Grassy";

public long color = Olive.BLACK;

private int oil = 3;

public int getOil() {

return oil;

}

public void setOil(int oil) {

this.oil = oil;

}

public Olive() {

System.out.println("Constructor of " + this.name);

}

public Olive(int oil) {

setOil(oil);

}

public int crush() {

System.out.println("crush from superclass");

//System.out.println("ouch!");

return oil;

}

Code: Kalamata.java

package com.lynda.olivepress.olives;

public class Kalamata extends Olive {

public Kalamata() {

super(2);

this.name = "Kalamata";

this.flavor = "Grassy";

this.color = Olive.BLACK;

}

//Annotation wth @...data type MUST match (super.crush())

@Override

public int crush() {

System.out.println("crush from subclass");

return super.crush();

}

Casting Objects

As in conversion...upward/downward (int -> long / long -> int)
casting

upcasting - subclass as superclass (SAFE)
downcasting - superclass as subclass (RISKY)

//Downcasting - will cause compiler error

Kalamata olive1 =olives.get(0);

//Downcasting Excplicitly

Kalamata olive1 = (Kalamata)olives.get(0);

Create a Kalamata() olive1 from Olive() in ArrayList[0], position 0

Kalamata olive1 = olives.get(0);

Create a Kalamata() olive1 from Kalamata() Olive() in ArrayList[0], position 0

Kalamata olive1 = (Kalamata)olives.get(0);

Code:

Main.java

//Downcasting

Kalamata olive1 = (Kalamata)olives.get(0);

//downcast Olive() to (Kalamata)

//(Kalamata)olives.get(0) means USE SUBCLASS

System.out.println("Olive 1 is from " + olive1.getOrigin());

Kalamata.java (only in the Kalamata subclass, not others..)

getOrigin extends Olive()

public String getOrigin() {

return "Greece";

}

Interfaces

Allows definition of classes’ structure

final fields
method names
return data type

Interfaces provides definition for creating classes

Allows for polymorphism due to similarities

Code:

This method only accept ArrayLists (part of Collection data type I/F)

public void getOil(ArrayList<Olive> olives) {}

This is more flexible and can take any Data Type that implements the Collection I/F

public void getOil(Collection<Olive> olives) {

Creating Interfaces

No constructor methods or other class elements
Modeling behavior, not dynamic managment of data
MUST BE PUBLIC

package com.lynda.olivepress.press;

public interface Press {

}

Creating a class with interface

Code:

package com.lynda.olivepress.press;

import java.util.Collection;

import com.lynda.olivepress.olives.Olive;

public class OlivePress2 implements Press {

@Override

public void getOil(Collection<Olive> olives) {

// TODO Auto-generated method stub

}

@Override

public int getTotalOil() {

// TODO Auto-generated method stub

return 0;

}

@Override

public void setTotalOil(int totalOil) {

// TODO Auto-generated method stub

}

File I/O: Copy a Text File

Code:

package com.lynda.files;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

public class CopyFile {

public static void main(String[] args) {

try {

// file is in the PROJECT directory

File f1 = new File("loremipsum.txt");

File f2 = new File("target.txt");

InputStream in = new FileInputStream(f1);

OutputStream out = new FileOutputStream(f2);

//Copy text file byte by byte..or by chunck of bytes

byte[] buf = new byte[1024];

int len; //holds bytes remaining

//reading information to fill the array

//return the total number of bytes received to len

while ((len = in.read(buf)) > 0) {

out.write(buf, 0, len);

}

in.close();

out.close();

System.out.println("File copied");

} catch (FileNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

ApacheFileUtils Library

Most developers put jars in the project’s \lib folder
Add to Build path: Access Denied

Clear Hidden Attribute
Set Everyone for ‘Full Control’

Code:

package com.lynda.files;

import java.io.BufferedInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.MalformedURLException;

import java.net.URL;

public class ReadNetworkFile {

public static void main(String[] args) {

try {

URL url = new URL("http://services.explorecalifornia.org/rss/tours.php");

InputStream stream = url.openStream();

BufferedInputStream buf = new BufferedInputStream(stream);

StringBuilder sb = new StringBuilder();

while (true) {

//buff.read will return number of character read

//will send -1 if end of file/stream

int data = buf.read();

if (data == -1) {

break;

}

else {

//convert data to char

sb.append((char)data); //Type Casting

}

System.out.println(sb);

} catch (MalformedURLException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

ParseXML

get jdom or use java base classes:

Code:

package com.lynda.files;

import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

public class ReadXML {

public static void main(String[] args) {

try {

DocumentBuilderFactory factory =

DocumentBuilderFactory.newInstance();

DocumentBuilder builder = factory.newDocumentBuilder();

Document doc = builder.parse("http://services.explorecalifornia.org/rss/tours.php");

NodeList list = doc.getElementsByTagName("title");

System.out.println("There are " + list.getLength() + " items");

for (int i = 0; i < list.getLength(); i++) {

Element item = (Element)list.item(i);

System.out.println(item.getFirstChild().getNodeValue());

}

} catch (ParserConfigurationException e) {

e.printStackTrace();

} catch (SAXException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

Creating JARs

Build Project
File > Export

Don’t select Eclipse .classpath or .project

For Debugging...select these

Manifest file has project metadata

ClassPath

Create a batch file and pass %1

set CLASSPATH=.

For Linux

D:\TEMP\Eclipse>java -classpath .:OlivePressApp.jar com.lynda.olivepress.Main

For Windows

D:\TEMP\Eclipse>java -classpath .;OlivePressApp.jar com.lynda.olivepress.Main

You crushed a Kalamata olive

You crushed a Ligurian olive

You crushed a Kalamata olive

You have 5 units of oil

You crushed a Kalamata olive

You crushed a Ligurian olive

You crushed a Kalamata olive

Now you have 10 units of oil

Olive 1 is from Greece

JavaDocs

Source > Generate Element Comment

/**

* @author SiloSix

File > Export > Java > JavaDoc

javadoc.exe: C:\Program Files\Java\jdk1.6.0_33\bin\javadoc.exe

Resources

apache commons

JUnit Class for testing:

Annotations

@Test, @Before, @After, @BeforeClass, @AfterClass, @Ignore

Code:

import static org.junit.Assert.*;

import org.junit.After;

import org.junit.AfterClass;

import org.junit.Before;

import org.junit.BeforeClass;

import org.junit.Ignore;

import org.junit.Test;

public class myJUnit1 {

//No main() method, so JUnit will take over

@BeforeClass

public static void mBeforeTestClass(){

System.out.println("--------ClassBegin------------------");

}

//Annotation: Before EACH @Test

@Before

public void mBeforeTest(){

System.out.println("--------------------------");

}

//Gets executed every time we run the JUnit program

@Test

public void test1(){

if (mMultiply(10,30)==300) {

System.out.println("Multiply Pass");

} else {

System.out.println("Multiply Fail");

fail("Multiply Failed for 10 and 30");

}

//Test 2 code

@Test

public void test2(){

if (mAdd(10,30)==300){

System.out.println("Add Pass");

} else {

System.out.println("Add Fail");

fail("Add Failed for 10 and 30");

}

//Test 3 code

@Test

public void test3(){

if(mDivide(10,30)==300) {

System.out.println("Divide Pass");

} else {

System.out.println("Divide Fail");

fail("Divide Failed for 10 and 30");

}

//Test 4 code won't run due to @Ignore

@Ignore

@Test

public void test4(){

if(mDivide(10,30)==300) {

System.out.println("Divide Pass");

} else {

System.out.println("Divide Fail");

fail("Divide Failed for 10 and 30");

}

// Runs after EACH @Test

@After

public void mAfterTest(){

System.out.println("--------------------------");

}

@AfterClass

public static void mAfterTestClass(){

System.out.println("---------Class End-----------------");

}

//Multiply

public int mMultiply(int x, int y){

return x*y;

}

//Add

public int mAdd(int x, int y){

return x+y;

}

//Divide

public double mDivide(int x, int y){

return x/y;

}

ECLIPSE

Installing Java and Eclipse on Ubuntu Linux: 2013 Updates

Do you have a JDK installed? You likely want to put $JDK_HOME/bin on your PATH, not the /bin of a JRE, as jar comes with JDK, not JRE.

Do this:

Delete all installations of Java.
Install the Java SDK (self-extracting) into /opt/jdk1.6.0_16 (for example)
Create a symbolic link: ln -s /opt/jdk1.6.0_16 /opt/jdk
Edit $HOME/.bashrc:

JAVA_HOME=/opt/jdk
PATH=$PATH:$HOME/bin:$JAVA_HOME/bin

Logout and log back in.

This offers many advantages:

You can install multiple versions of the SDK and need only switch a symbolic link.
You know where all the files are located.
You know exactly which version of Java is being used.
No other versions are installed, so there cannot be any conflicts.

I have done this for years and have never had any problems with Java on Linux, except for packages that do not detect that Java is installed and attempt to install the OpenJDK.

Also, stay away from the OpenJDK as its fonts are terrible to behold.

Environment Preparation

JavaSE 6r29 JDK(and JRE): java.oracle.com
Set Path & Test: “C:\Program Files\Java\jre6\bin”

java -version
javac -version

Eclipse: www.eclipse.org/downloads

Eclipse IDE for Java Developers/Jave EE Developers

JARs(include in Eclipse project when needed):

TestND: http://beust.com/eclipse
Java Excel API: http://jexcelapi.sourceforge.net/

http://jexcelapi.sourceforge.net/resources/javadocs/2_3_8/docs/jxl/read/biff/BiffException.html

JUnit: http://www.junit.org/
Apache ANT (HTML reporting)

Subversion http://subclipse.tigris.org/update_1.8.x

Also check: http://download.eclipse.org/releases/juno/

Help and Tutorials

Java/Selenium Reading from Excel sheets:

Shortcuts:

CTRL-SPACE Code writing

CTRL + / Add/remove comments

CTRL + SHFT + O Organize imports (Add/remove imports)

ALT + UP/DOWN Move a line of code up or down

CTRL + D Delete Line

ALT+SHFT+J Element Comment

Eclipse Start.bat: JDK7

This uses the JDK7 binaries:

set DEV_HOME=D:\DEVL\Java

set JAVA_HOME=%DEV_HOME%\java32\jdk7

set PATH=%JAVA_HOME%\bin;%PATH%

start %DEV_HOME%\eclipse32\eclipse.exe -vm %JAVA_HOME%\bin\javaw.exe -showlocation -vmargs -server -Xms512m -Xmx1024m -XX:MaxPermSize=128m

Eclipse.ini Configuration: JDK7

-startup

plugins/org.eclipse.equinox.launcher_1.3.0.v20120522-1813.jar

--launcher.library

plugins/org.eclipse.equinox.launcher.win32.win32.x86_1.1.200.v20120522-1813

-product

org.eclipse.epp.package.java.product

--launcher.defaultAction

openFile

--launcher.XXMaxPermSize

256M

-showsplash

org.eclipse.platform

--launcher.XXMaxPermSize

256m

--launcher.defaultAction

openFile

-vm

D:/DEVL/Java/java32/java32/jdk7/bin/javaw.exe

-vmargs

-Dosgi.requiredJavaVersion=1.5

-Dhelp.lucene.tokenizer=standard

-Xms40m

-Xmx512m

HOME Environment Variable

Installing the Subversion Client

Go to Help\Eclipse Marketplace and search by ‘Subversion’
Select Subclipse and Install…
http://subclipse.tigris.org/update_1.8.x

Go to Preferences\Team\SVN
The SVN interface should be JavaHL(JNI)
Here it is Not Available

If the Subclipse client plugins are missing, the following prompt will appear

Subclipse Library Not Available

Installing Subclipse from Help\New Software

Go to Help\Install New Software…

Locate “Subclipse – http://...”

Select Subclipse option, Click Next

Acknowledge EULAs

Eclipse will download selected packages

Security Warning

Eclipse will restart

Installing Subclipse From Help\Eclipse Market Place…

Eclipse Marketplace: Subclipse selection

Select all packages

Acknowledge the EULAs

Eclipse will download the packages

Upon restarting, Eclipse will prompt for communicating Subclipse usage

Enabling the SVN Connector and Plugin

Eclipse\Preferences\Team\SVN

Select SVN interface: JavaHL and press OK

$D:\ASSETS\CAPTURE\screenshot.358.jpg$

Open the SVN Repository View

The SVN repository Exporting Panel will appear

Right Click in the SVN repositories panel, select New..

Enter the URL of the SVN Server and Repository

If Incorrect, Eclipse will indicate an Error

Accessing SVN from the Project Explorer

Eclipse About

About Main Form

Installation Details

Installation History

Features

Plugins

Eclipse Installation Details

Eclipse Help

Main Contents View

Help Contents Expanded

Help Index

Help Search

Compiling and Running

Java package statement implies the directory structure where it exists within the project.

Should be unique

package com.lynda.javatraining;
\src\com\lynda\javatraining\HelloWorld.java

When compiling, use javac in the project root:

C:\JavaProjects\HelloWorld>javac com\lynda\javatraining\HelloWorld.java

HelloWorld.class
HelloWorld.java

When running, use package reference and filename without “.java” extension

C:\JavaProjects\HellowWorld>java com.lynda.javatraining.HelloWorld

public class HelloWorld {

public static void main(String[] args) {

Static: allows class to be called directly?

public class HelloWorld {

public static void main(String[] args) {

Static: allows class to be called directly?

Eclipse Development

Create Workspace

Create WORKSPACE folder to contain PROJECTS
New, Project....
New, Class....(.java file is the class)

Window > Prefrences > General > Appearance > Colors and Fonts.. > Text Font
Run > Run Configurations... >

Import Projects

File > Import > General > Existing Project into Workspace

Exploded Project (Root Dir)
Zipped Project (Archive File)
Root Dir, OK
Eclipse will autodetect projects
Copy projects into workspace

Close projects that aren’t in use (Right-Click, Close Project)

Projects remain in workspace, just not open

IDE Layout

HutuBBB

Views/Panels

Perspectives

Arrangement of Views
Custom Perspectives: Window > Save Perspective As....

Command Line

Dir to PROJECT\SRC
javac Main.java

dir = Main.class
java Main

javac Main.java -d ..\bin

\src\Main.class

javac Main.java -verbose

Note: Access Denied Errors

If Access Denied error occurs, set folder permissions to Everyone and give Full Control access.

D:\Eclipse\Java\CommandLine\src>javac Main.java -d D:\Eclipse\Java\CommandLine\bin

Main.java:2: error while writing Main: D:\Eclipse\Java\CommandLine\bin\Main.class (Access is denied

public class Main {

ClassPath

Similar to the classic dynamic loading behavior, when executing Java programs, the Java Virtual Machine finds and loads classes lazily (it loads the bytecode of a class only when this class is first used). The classpath tells Java where to look in the filesystem for files defining these classes.

The virtual machine searches for and loads classes in this order:

bootstrap classes: the classes that are fundamental to the Java Platform (comprising the public classes of the Java Class Library, and the private classes that are necessary for this library to be functional).
extension classes: packages that are in the extension directory of the JRE or JDK, jre/lib/ext/
user-defined packages and libraries

By default only the packages of the JDK standard API and extension packages are accessible without needing to set where to find them. The path for all user-defined packages and libraries must be set in the command-line (or in the Manifest associated with the Jar file containing the classes).

Setting the path through an environment variable

The environment variable named CLASSPATH may be alternatively used to set the classpath. For the above example, we could also use on Windows:

Sometimes you have to check the JAVA_HOME also, if it is pointing towards the right JDK version

set CLASSPATH=D:\myprogram
java org.mypackage.HelloWorld

Diagnose

Application programmers may want to find out/debug the current settings under which the application is running:

System.getProperty("java.class.path")

XXX

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