Object Oriented Programming in Java Lecture 14

Review Quiz 1. 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 { boolean add(Element o) { // code omitted } Element getFirst(){ // code omitted }

Examples public class Ex2 { private void testCollection() { List list = new ArrayList (); 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 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 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); Input Scanner 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;