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

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

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:

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(){

Creating JARs

• Build Project
• File > Export

Don’t select Eclipse .classpath or .project

For Debugging...select these

Manifest file has project metadata

ApacheFileUtils Library

• http://commons.apache.org/proper/commons-io/
  • http://apache.mirrors.lucidnetworks.net/commons/
  • http://apache.mirrors.lucidnetworks.net/commons/io/binaries/commons-io-2.6-bin.tar.gz
• http://commons.apache.org/proper/commons-io/javadocs/api-release/index.html
• Most developers put jars in the project’s \lib folder
• Add to Build path: Access Denied
  • Clear Hidden Attribute
  • Set Everyone for ‘Full Control’

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 {

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
• While <ArrayList> might be declared & used in the main logic,
  • helper classes can use Collection<T> so that other data types can be fed to it
  • such as
    • HashMap, Array, Enum

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);

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;