Classes. Interfaces. Inheritance презентация

Java. Inheritance IT Academy

Agenda Classes. Interfaces. Abstract Classes Inheritance in Java Polymorphism Java Classes. Examples

Abstract Classes A class must be declared abstract when it has one or more abstract methods. A method is declared abstract when it has a method heading, but no body – which means that an abstract method has no implementation code inside curly braces like normal methods do. The derived class must provide a definition method; The derived class must be declared abstract itself. A non abstract class is called a concrete class.

Abstract Classes /* The Figure class must be declared as abstract because it contains an abstract method */ public abstract class Figure { /* because this is an abstract method the body will be blank */ public abstract double getArea(); } public class Circle extends Figure { private double radius; public Circle (double radius) { this.radius = radius; public double getArea() { return (3.14 * (radius * 2)); } }

Classes. Abstract Classes public class Rectangle extends Figure { private double length, width; // public Rectangle(double length, double width) { this.length = lengt; this.width = width; } // public double getArea() { return length * width; } }

Interfaces An interface differs from an abstract class because an interface is not a class. An interface is essentially a type that can be satisfied by any class that implements the interface. Any class that implements an interface must satisfy 2 conditions It must have the phrase "implements Interface_Name" at the beginning of the class definiton; It must implement all of the method headings listed in the interface definition.

Interfaces public interface Dog { public boolean Barks(); public boolean isGoldenRetriever(); } public class SomeClass implements Dog { public boolean Barks() { // method definition here } public boolean isGoldenRetriever() { // method definition here } }

Inheritance in Java Assignment operator. What will be done ? int num=1; double data=1.0; data=num; // num=data; ??? class Aclass { int field1=10; } class Bclass extends Aclass { int field2=20; } Aclass a=new Aclass( ); Bclass b=new Bclass( ); a=b; // b=a; ??? // a = new Bclass( );

Inheritance in Java public class ClassA { public int i=1; public void m1() { System.out.println("ClassA, metod m1, i="+i); } public void m2() { System.out.println("ClassA, metod m2, i="+i); } public void m3() { System.out.print("ClassA, metod m3, runnind m4(): "); m4(); } public void m4() { System.out.println("ClassA, metod m4"); } }

Inheritance in Java public class ClassB extends ClassA { public double i=1.1; public void m1() { System.out.println("ClassB, metod m1, i="+i); } public void m4() { System.out.println("ClassB, metod m4"); } } Automatically added default constructor.

Inheritance in Java public class ApplAB { public static void main(String[] args) { System.out.println("The Start."); ClassA a; ClassA b; a=new ClassA(); b=new ClassB(); System.out.println("Test ClassA."); a.m1(); a.m2(); a.m3(); a.m4();

Inheritance in Java System.out.println("Test ClassB."); b.m1(); b.m2(); b.m3(); b.m4(); ClassB b0; b0=new ClassB(); System.out.println("Test_0 ClassB."); b0.m1(); b0.m2(); b0.m3(); b0.m4(); System.out.println("The End."); } }

Inheritance in Java The Start. Test ClassA. ClassA, metod m1, i=1 ClassA, metod m2, i=1 ClassA, metod m3, runnind m4(): ClassA, metod m4 ClassA, metod m4 Test ClassB. ClassB, metod m1, i=1.1 ClassA, metod m2, i=1 ClassA, metod m3, runnind m4(): ClassB, metod m4 ClassB, metod m4 Test_0 ClassB. ClassB, metod m1, i=1.1 ClassA, metod m2, i=1 ClassA, metod m3, runnind m4(): ClassB, metod m4 ClassB, metod m4 The End.

Polymorphism package com.softserve.train; public abstract class ACar { private double maxSpeed; public double getMaxSpeed( ) { return maxSpeed; } public void setMaxSpeed(double maxSpeed) { this.maxSpeed = maxSpeed; } abstract void carRides( ); }

Polymorphism public class BmwX6 extends ACar { public BmwX6( ) { } @Override public void carRides( ) { setMaxSpeed(200); System.out.println("Car Rides"); workedEngine( ); workedGearBox( ); } public void workedEngine( ) { System.out.println("BmwX6: Engine Running on Petrol."); System.out.println("BmwX6: Max Speed: " + getMaxSpeed( )); }

Polymorphism private void workedGearBox( ) { System.out.println("BmwX6: Worked GearBox."); } public void lightsShine( ) { System.out.println("BmwX6: Halogen Headlights."); } } inheritance of private fields and methods ?

Polymorphism package com.softserve.train; public class BmwX6mod extends BmwX6 { public BmwX6mod( ) { super( ); } @Override public void workedEngine( ) { System.out.println("BmwX6mod: Engine Running on Diesel."); System.out.println("BmwX6mod: Max Speed: " + getMaxSpeed( )); } @Override public void lightsShine( ) { System.out.println("BmwX6mod: Xenon Headlights."); super.lightsShine(); } }

Polymorphism package com.softserve.train; public class Appl { public static void main(String[ ] args) { ACar carX6 = new BmwX6( ); ACar carX6mod = new BmwX6mod( ); BmwX6 carX6mod2 = new BmwX6mod( ); carX6.carRides( ); ((BmwX6)carX6).lightsShine( ); carX6mod.carRides( ); ((BmwX6)carX6mod).lightsShine( ); carX6mod2.carRides( ); carX6mod2.lightsShine( ); } }

Java Classes What is wrong in the code ? package com.softserve.train; public class Parent { int f( ) { return 1; } } public int f( ) { … what will in case ???

Java Classes package com.softserve.train2; import com.softserve.train.Parent; public class Child extends com.softserve.train.Parent { int f( ) { return 2; } } protected int f( ) { … what will in case ???

Java Classes package com.softserve.train; import com.softserve.train2.Child; public class Grandchild extends com.softserve.train2.Child { public int y( ) { return this.f( ); // ??? } }

Java Classes package com.softserve.train; public class Appl { public static void main(String[] args) { Grandchild g = new Grandchild(); boolean result = (g.f( ) == g.y( )); // ??? System.out.println("result=" + result); } }