Object Oriented Programmingin

Java

Lecture 14

Review Quiz1. Write a method which gets an Object

and call all its available ‘get’ Methods and print the return values.

Java 5 new Features

• Ease of development

• Quality monitoring and manageability

• Performance and scalability

Generics

• Allow to pass types as arguments to classes just as values to methods

Why ?

- compile time safety

- no need in casts

C++: templates are handled on macro processor level

Examples

public class LinkedList <Element>{

boolean add(Element o) {

// code omitted

}

Element getFirst(){

// code omitted

}

}

Examplespublic class Ex2 {

private void testCollection() { List<String> list = new ArrayList<String>(); list.add(new String("Hello world!")); list.add(new String("Good bye!")); list.add(""+new Integer(66)); printCollection(list); }

private void printCollection(Collection c) { Iterator<String> i = c.iterator(); while(i.hasNext()) { String item = i.next(); System.out.println("Item: "+item); } }

public static void main(String argv[]) { Ex2 e = new Ex2(); e.testCollection(); }}

Examples

Advantages

• Allow to pass types as arguments to classes just as values to methods

Why ?

- compile time safety

- no need in casts

Enhanced loop

Syntax

for (FormalParameter : Expression) Statement

Note:Expression must be an array or an instance of a new interface called java.lang.Iterable

public void oldFor(Collection c) { for(Iterator i = c.iterator(); i.hasNtext(); ) { String str = (String) i.next(); System.out.println(str); }}

public void newFor(Collection<String> c) { for(String str : c){

System.out.println(str); }

}

public int sumArray(int array[]) { int sum = 0; for(int i=0;i<array.length;i++)

sum += array[i]; return sum; }-------------------------------------------------- public int sumArray(int array[]) {

int sum = 0; for(int i : array)

sum += i;

return sum; }

Loops for arrays

Static imports

Enable to import methods and fields from the static members of the class or interface, without qualifying the name

import static java.lang.System.out;

……….. out.print("stuff"); out.print("more stuff");

Var-args

Multiple arguments can be passed to the routines:

public static void myMethod(Object ... args){ for(Object a:args) System.out.print(""+a+" "); System.out.println();} … myMethod(23, 34, 78,"Hello", "Goodbye"); System.out.printf("%d %d %d %s %s",23, 34, 78,"Hello",

"Goodbye");

Input/Output

• Output

System.out.printf("%s %3d", name, age);

• InputScanner reader = new Scanner(System.in);

int n = reader.nextInt();

Enumerations

Example:enum Drinks {pepsi, coke, schweppes };….Drinks d = Drinks.coke;System.out.print(d); ….Note:In C++ enumerations are just hidden integers.In Java enumerations are generated classes.

Example

public enum Shapes{ins1(1,2),ins2(1,3) ;private int x;private int y;Shapes(int x, int y){

this.x = x;this.y = y;

}}

…..

Shapes s = Shapes.ins1;

Shapes s2 Shapes.ins2;