Object-Oriented Java ProgrammingWhy Java?Objects, Classes, and MethodsConstructors OverloadingAccess ControlExample of Access ControlInheritanceClass ObjectMethod equals ( )Overide equals ( )Method toString( )Overide toString( )Slide 13Inheritance (Cont’d)Slide 15CastingExample of CastingDynamic BindingDynamic Binding ExampleDynamic Binding Example (Cont’d)Abstract ClassExample of Abstract ClassInterfaceInterface ExampleInterface Example (Cont’d)Slide 26Slide 27Interface (Java) vs. Multiple Inheritance (C++)Interfaces vs. Abstract ClassesCombination of Abstract Class and InterfaceString ProcessingImportant Methods in Class StringSlide 33Class StringBufferImportant Methods in StringBufferImportant Methods in Class StringBufferClass StringTokenizerImportant Methods in Class StringTokenizerCSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 1Object-Oriented Java ProgrammingCSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 2Why Java?•Simple•Platform Independent•Safe•Multi-Threaded•Garbage CollectedCSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 3Objects, Classes, and Methods•ObjectSomething that occupies memory and has a state•ClassPattern (type) of object•MethodFunction and procedure to access object stateCSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 4Constructors Overloadingpublic class Point{ … }public class Rectangle{ private int width = 0; private int height = 0; private Point origin; public Rectangle() { origin = new Point(0, 0); } public Rectangle(Point p, int w, int h) { origin = p; width = w; height = h; } …}CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 5Access Control•Public:•Private:•Protected:•Package:CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 6Example of Access ControlBase.javapackage p1; public class Base{ private int u; protected int v; public int w; private void g ( ) { System.out.println(v); } protected void f ( ) { System.out.println(u); g(); }}Derived.javapackage p2;import p1.Base;public class Derived extends Base{ void h () { f(); } void k () { g(); }}Test.javapackage p2;import p1.Base;public class Test { public static void main(String[] args) { Base b = new Base(); b.u = 1; // Compilation error b. v = 2; // Compilation error b.w = 3; // OK b.g(); // Compilation error b.f(); // Compilation error Derived d = new Derived(); d.h(); // OK d.k(); // Compilation error }}CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 7Inheritancepublic class B extends A {…}public class A {…}ShapeTwoDimensionalShape ThreeDimensionalShapeCircle Square Triangle Sphere CubeObjectCSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 8Class Objectclass Object { … public boolean equals ( Object obj ) { … } public String toString() { …} …}CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 9Method equals ( )•==: identical references to objects String s = “Hello”;String t = new String(“Hello”); if ( s == t ) System.out.println( “the same”); // condition is false and print nothing! if ( s.equals(t) ) System.out.println( “the same”);•equals: equality of objects–Already implemented in class Object–Need to define for your class :Point p1 = new Point (10, 10);Point p2 = new Point (5, 5);Rectangle rec1 = new Rectangle (p1, 5,10);Rectangle rec2 = new Rectnagle (p2, 5, 10);if ( rec1 == rec2 ) System.out.println(“the same”); // condition is false and print nothing!if ( rec1.equals(rec2) ) System.out.println(“the same”);CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 10Overide equals ( ) public class Rectangle{ … public boolean equals ( Object obj ) { Rectangle rec = (Rectangle) obj; return (w == rec.width()) && (h == rec.height());}} Rectangle rec1 = new Rectangle (p1, 5, 10); Rectangle rec2 = new Rectangle (p2, 5, 10);if ( rec1.equals(rec2) ) System.out.println(“the same!”); // condition is true and print “the same”!CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 11Method toString( )Rectangle rec = new Rectangle (p1, 5, 10);System.out.println( rec );// prints something like Rectangle@73d6at(class name +@+ hash code of object)CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 12Overide toString( )public class Rectangle{ …public String toString() { return “width = ” + w + “, height = ” + h;}} Rectangle rec = new Rectangle (p1, 5, 10); System.out.println( rec );Output: width = 5, height = 10 (instead of Rectangle@73d6at)CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 13Inheritancepublic class Circle{ private Point center; private double radius; public Circle( Point c, double r) { center = c; radius = r; } public double area() { return Math.PI * radius* radius; }}public class Rectangle{ private Point center; private double width; private double height; public Rectangle( Point c, double w, double h) { center = c; width = w; height = h; } public double area() { return width * height; }}CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 14Inheritance (Cont’d)public abstract class Shape{ private Point center; public Shape( Point c) { center = c; } public abstract double area();}CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He 15Inheritance (Cont’d)public class Circle extends Shape{ public Circle( Point c, double r) {super(c); radius = r; } public double area() { return Math.PI * radius* radius;}}public class Rectangle extends Shape{ private double width; private double height; public Rectangle( Point c, double w, double h){ super(c); width = w; height = h; } public double area() { return width * height; }}CSE3302 Programming Languages Object-Oriented Java Programming Spring 2008 ©Weimin He
View Full Document
Unlocking...