2022年09月26日Java上机

运行不了需要建立包，多个文件都包含A类，不建立包会冲突

运行不了需要建立包，多个文件都包含A类，不建立包会冲突

运行不了需要建立包，多个文件都包含A类，不建立包会冲突

示例4-1

JBT4101

class Animal {
    public float weight;

    public void eat() {
        System.out.println("eat......");
    }
}

class Mammal extends Animal {
    public int heartRate;

    public void breath() {
        System.out.println("breath......");
    }
}

class Cat extends Mammal {
    boolean longHair;

    public void purr() {
        System.out.println("purr......");
    }
}

public class JBT4101 {
    public static void main(String args[]) {
        Cat obj = new Cat();
        obj.eat();
        obj.breath();
        obj.purr();
    }
}

示例4-9

JBT4106.java

class A {
	protected  double y=2.13;
	void set1(int y){
		this.y=y;
	}
}
class B extends A {
	int y=0;
	void show( ){
		y=y+10;
		System.out.println("y="+y);
	}
	void set2(int y){
		this.y=y;
	}
}
class JBT4106 {    
	public static void main(String args[ ]){
		B  b=new B();
		b.set1(-20);
		b.show();
		b.set2(-20);
		b.show( );
	}  
}

示例4-13

JBT4110

class A {
    int x, y;

    void add(int x, int y) {   //note1
        System.out.println(x + "+" + y + "=" + (x + y + 100));
    }

    void add(float x, float y) { //note2
        System.out.println(x + "+" + y + "=" + (x + y + 200));
    }
}

class B extends A {
    void add(int x, long y) {  //note3
        System.out.println(x + "+" + y + "=" + (x + y + 300));
    }

    void add(long x, int y) {  //note4
        System.out.println(x + "+" + y + "=" + (x + y + 400));
    }

    void add(int x, int y) {   //note5
        System.out.println(x + "+" + y + "=" + (x + y + 500));
    }


}

public class JBT4110 {
    public static void main(String args[]) {
        B b = new B();
        b.add(1, 2);          //call 1
        b.add(1.0f, 2.0f);    //call 2
        b.add(1, 2L);        //call 3
        b.add(1L, 2);       //call 4
    }
}

示例4-19

JBT4201

abstract class Shape {
    public int x, y;
    public int width, height;

    public Shape(int x1, int y1, int width1, int height1) {
        x = x1;
        y = y1;
        width = width1;
        height = height1;
    }

    abstract double getArea();        //抽象方法，只能声明

    abstract double getPerimeter();        //抽象方法，只能声明
}

class Square extends Shape {
    public double getArea() {
        return (width * height);
    }

    public double getPerimeter() {
        return (2 * width + 2 * height);
    }

    Square(int x, int y, int width, int height) {
        super(x, y, width, height);
    }
}

class Circle extends Shape {
    public double r;

    public double getArea() {
        return (r * r * Math.PI);
    }

    public double getPerimeter() {
        return (2 * Math.PI * r);
    }

    Circle(int x, int y, int width, int height) {
        super(x, y, width, height);
        r = (double) width / 2.0;
    }
}

public class JBT4201 {
    public static void main(String args[]) {
        Square box = new Square(5, 15, 20, 20);
        Circle oval = new Circle(5, 50, 20, 20);
        System.out.println("Box Area==" + box.getArea());
        System.out.println("Oval Area==" + oval.getArea());
    }
}

示例4-21

JBT4202B

interface A {
    char cha = 'A';

    public void showA();
}

interface B {
    char chb = 'B';

    public void showB();
}

interface C extends A, B {
    char chc = 'C';

    public void showC();
}

interface D {
    char chd = 'D';
}

class TestInterface implements C {
    public void showA() {
        System.out.println(cha);
    }

    public void showB() {
        System.out.println(chb);
    }

    public void showC() {
        System.out.println(chc);
    }
}

public class JBT4202B {
    public static void main(String[] args) {
        TestInterface obj = new TestInterface();
        System.out.println(D.chd);
        obj.showA();
        obj.showB();
        obj.showC();
    }
}

示例4-22

JBT4203

interface ShowMessage {
    void show(String s);            //接口中的方法默认都是public
}

class Car implements ShowMessage {
    public void show(String s) {        //在使用接口的类中要显式表示public 
        System.out.println("Car=" + s);
    }
}

class Bicycle implements ShowMessage {
    public void show(String s) {        //在使用接口的类中要显式表示public
        System.out.println("Bicycle=" + s);
    }
}

public class JBT4203 {
    public static void main(String args[]) {
        ShowMessage dm;            //声明接口变量
        dm = new Car();            //接口变量中存放对象的引用
        dm.show("奔驰");        //接口回调
        dm = new Bicycle();            //接口变量中存放对象的引用
        dm.show("捷安特");        //接口回调
    }
}