georgia institute of technology what is new in java 5.0 (1.5)? barb ericson georgia institute of...

Georgia Institute of Technology

What is new in Java 5.0 (1.5)?

Barb EricsonGeorgia Institute of Technology

June 2006

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Learning Goals

• Understand the new features in Java 5.0– For-each loop– Generics– Automatic Boxing and Unboxing– New collection interfaces – Not covered on exam

• Enumerated Types• Static Imports• Formatted Input and Output

– For more information see http://apcentral.collegeboard.com/members/article/1,3046,151-165-0-49154,00.html

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For Each Loop

• Used to loop through all items of a collection (Array, List, Map, Set, etc)– Syntax

for (Type varName : collectionName)

– Examplefor (String name : nameList)

– Each time through the loop the varName will refer to a different item in the collection until all the items in the collection have been processed

– Use whenever you want to process each item in a collection

• But not when you might want to remove an item from the collection in the loop

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Before the For-Each Loop/** * Method to set all the sample values to * the maximum positive * value if they were positive (including 0) * and the minimum * negative value if they were negative. */ public void forceToExtremes() { SoundSample[] sampleArray =

this.getSamples(); SoundSample sample = null;

// loop through the sample values for (int i = 0; i < sampleArray.length; i++) { // get the current sample sample = sampleArray[i];

/* if the value was >= 0 set to the * maximum positive value */ if (sample.getValue() >= 0) sample.setValue(32767); /* else (must be less than 0) so set it to * the highest negative value */ else sample.setValue(-32768); } }

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Using for-each instead

• Replace the following SoundSample sample = null;

// loop through the sample values

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

{

// get the current sample

sample = sampleArray[i];

• With for (SoundSample sample : sampleArray)

{

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Exercise• Copy the code for forceToExtremes and put it in

Sound.java in the bookClasses directory• Test it with the following in the main:

String file = FileChooser.pickAFile();Sound s = new Sound(file);s.explore();s.play();s.forceToExtremes()s.explore();s.play();

• Change the code in forceToExtremes to use a for-each loop instead and test again

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Exercise• Modify a method in the Picture class that modifies all pixels in a picture to use a for-each loop

public void negate() { Pixel[] pixelArray = this.getPixels(); Pixel pixel = null; int redValue, blueValue, greenValue = 0;

// loop through all the pixels for (int i = 0; i < pixelArray.length; i++) { // get the current pixel pixel = pixelArray[i];

// get the current red, green, and blue values redValue = pixel.getRed(); greenValue = pixel.getGreen(); blueValue = pixel.getBlue();

// set the pixel's color to the new color pixel.setColor(new Color(255 - redValue, 255 - greenValue, 255 - blueValue)); } }

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Generics

• Allow you to specify the type of objects in a collection, both when you declare it and create it– Eliminates the need to downcast– Syntax:

• CollectionType<Type> name = new CollectionType<Type>;

– List<String> nameList = new ArrayList<String>();

• CollectionType<Type,Type> name = new CollectionType<Type,Type>;

– Map<String,String> phoneMap = new HashMap<String,String>();

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Without Generics

• You have to cast back to the original class when you get an object back from a collection – Downcast from Object

name = (String) iterator.next();

• With generics you don't have to downcast– Just give the type on declarations and

creationname = iterator.next();

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Exercise

• Modify the SlideShow class in examples/SlideShow-List

• Use generics instead of casting – Specify the type on all declarations of the List

• Including parameters

– Specify the type on the creating of the List– Remove the cast to Picture when you show

the pictures or get the picture– You can use a for-each loop instead of an

iterator when showing the pictures

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Exercise

• Modify the PhoneBook class in examples/PhoneBook to use generics for the phoneMap– Copy the code to change first– Then comment out the old code– Add new code for generics

• Be sure to specify the type when you declare the phoneMap and when you create it

• Remove the downcast on getting items from the map

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Automatic Boxing and Unboxing

• Primative types are not objects: – int, double, char, boolean– They can not be added to collections

• You can have arrays of primitive types

– But, they can be wrapped and added to collections (Integer, Double, Character, Boolean)

• And then you have to unwrap to get the value

• With automatic boxing and unboxing you don't have to worry about the wrapping and unwrapping– It is done for you

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Example of Boxing and Unboxing

• Add a primitive type to a collection– Old way: wrapping the primitive type

• List intList = new ArrayList();• intList.add(new Integer(5));• intList.add(new Integer(6));• Integer integerValue = (Integer) intList.get(0);• int value = integerValue.intValue();

– New: auto wrapping (boxing)• List intList = new ArrayList();• intList.add(5);• intList.add(6);• int value = (Integer) intList.get(0);

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New Queue Interface

• Java 5.0 adds a Queue interface– Implemented by the LinkedList class– Implemented by the PriorityQueue class

• There are no more special AP interfaces for AB data structures– Only using the Java interfaces and classes

• Stack (class), Queue (interface), PriorityQueue (class)

– Using new method names for queues» peek, add, and remove

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Not Covered on Exam• Enumerated Types

– Old: declare constants using numbers• public static final int MALE = 0;• public static final int FEMALE = 1;

– New: use enumerated types• public enum Gender { MALE, FEMALE };

• Static Imports– Old: Use class name to access constants

• Color.BLACK

– New: import static java.awt.*;• BLACK

• Formatted Input and Output– Use java.io.Scanner class to read from a file or System.in – See System.out.printf() to format output

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Summary

• Java 5.0 adds many new features– Tested on the Exam

• For-each loop– for (Type varName : collectionName)

• Generics– Give the type when you declare and create collection

objects– List<String> nameList = new ArrayList<String>();– Eliminates the need to downcast from Object