1. Barb Ericson Georgia Institute of Technology June 2006
What is new in Java 5.0 (1.5)?
Barb Ericson
Georgia Institute of Technology
June 2006
Georgia Institute of Technology

2. Georgia Institute of Technology
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
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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)
Example
for (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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4. 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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5. 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()
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 creation
name = 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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11. Georgia Institute of Technology
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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12. Automatic Boxing and Unboxing
Private 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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13. 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)
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
Be careful not to use methods that are valid in Java for Stacks, Queues, and PriorityQueues but not normally part of these data structures.
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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
Auto-boxing and unboxing
Don't need to explicitly add primitive values to wrapper classes and get the value back out
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