Java 5 Information

From Kb

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1 For Each Loop
2 Annotations
3 Static Imports
4 Assertions
5 Generics
6 Enums
7 Java 5 JVM Arguments
8 Threads

For Each Loop

void doSomeLoop(Collection<TimerTask> c) {
    for (TimerTask t : c){
        t.doSomething();
    }
}

More information on Sun Java Site: http://java.sun.com/j2se/1.5.0/docs/guide/language/foreach.html

Annotations

More annotation information on Java 5 Tutorial Page
Supress Warnings from compiler about unchecked casts and deprecated code

@SuppressWarnings({"unchecked", "deprecation"})

Static Imports

Able to import a static method from another Class

import static MyClass.someStaticMethod;
import static MyClass.*; //all methods

Can call it using someStaticMethod() instead of having to go MyClass.someStaticMethod()

Assertions

assert (someParam!=null);

Generics

Dynamically set return types - example from EasyMock

/**
  * Creates a mock object that implements the given interface, order checking
  * is enabled by default.
  * 
  * @param <T>
  *            the interface that the mock object should implement.
  * @param toMock
  *            the class of the interface that the mock object should
  *            implement.
  * @return the mock object.
  */
  public static <T> T createStrictMock(Class<T> toMock) {
      return createStrictControl().createMock(toMock);
   }

Enums

Java Enum and the Switch Statement

Can't use constants (even if they are int's) in a Switch statement, use Enum instead
Samples taken from here. Sun's Enum overview is also quite useful. Sun Enum Javadoc gives more info.
To declare the Enum

public enum Shape { RECTANGLE, CIRCLE, LINE }

To use in the switch statement

switch (drawing) {
    case RECTANGLE: g.drawRect(x, y, width, height);
                    break;
    case CIRCLE   : g.drawOval(x, y, width, height);
                    break;
    case LINE     : g.drawLine(x, y, x + width, y + height);
                    break;
    default: // could be used, but in general we cover all the members of the Enum above
}

Looping over Enums

for (Shape shp : Shape.values()) {
    System.out.println(shp);       // Prints RECTANGLE, CIRCLE, ...
}

Refactoring (Integer) constants to Java Enum for use in the Switch Statement

Problem: You want to do the bar minimum to use a switch statement with constants.
Solution: Code something similar to the following.
- Note that this probably doesn't save time as a one-off, but can be useful if this code is used repeatedly, or if you need a half-way house while refactoring (part) of your code.

/**
	 * Define an Enum (private) so that we can convert the int(eger) for use in a Switch statement
	 * Normally Java needs a hard coded value in the switch statement , and will not accept a constant 
	 * (even if it is private static final int)
         * This can be defined in it's own file, or included at the bottom of a public class file
	 */	
	enum Page{
 
		PAGE_START(PageConstants.Page1), //where PageConstants give the (int) values we wish to convert
		PAGE_MIDDLE(PageConstants.Page),
		PAGE_END(PageConstants.Page2)
 
		private int pageInt; //internal holder
 
		/**
		 * Enum constructor so that we can generate a suitable Enum value based on the int
		 * @param page
		 */
		Page(int pageIndex){
			this.pageInt=pageIndex;
		}
 
		/**
                 * static convenience method to create Page Enum based on the int value passed in
                 * we check if we can match the int value passed in to one of the constants in our collection.
                */
		static Page valueOf(int pageValue){
 
			for (Page p: Page.values()) {
 
			    if(p.pageInt()== pageValue){
			    	return p;
			    }
 
			}
			throw new AssertionError("Unknown page value: " + pageValue);
 
	    }
 
	}

then to use (code snippet)

//Convert int to Enum
Page thisPage = Page.valueOf(thisPageInt);
 
// Now use the enum in the switch statement
switch(thisPage){
	case PAGE_START: /*do something */;break;
	case PAGE_END: /*do something */;break;
	default: //do nothing
}

Java 5 JVM Arguments

Memory Size

-Xmsn : Specify the initial size, in bytes, of the memory allocation pool. This value must be a multiple of 1024 greater than 1MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is 2MB. Examples:
- -Xms384M
Specify the maximum size, in bytes, of the memory allocation pool. This value must a multiple of 1024 greater than 2MB. Append the letter k or K to indicate kilobytes, or m or M to indicate megabytes. The default value is 64MB. Example
- -Xmx768m
Size of the Permanent Generation. 5.0 and newer: 64 bit VMs are scaled 30% larger; 1.4 amd64: 96m; 1.3.1 -client: 32m.
- More info at http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp
- -XX:MaxPermSize=512M