利用编程语言解决问题的四个层次

第1层次(普通的语句)

package com.jd.uos.test;

public class AnyIdeaAplication {
    public static void main(String[] args) {
        double radius = 10;
        System.out.println("圆的面积:\t" + Math.PI * Math.pow(radius, 2));
        System.out.println("圆的面积:\t" + 2 * Math.PI * radius);
    }

}

第2层次(方法/函数的视角)

package com.jd.uos.test;

public class AnyIdeaAplication {
    static double getArea(double r){
        return Math.PI * Math.pow(r, 2);
    }

    static double getCircumstance(double r){
        return 2 * Math.PI * r;
    }
    public static void main(String[] args) {
        double radius = 10;
        System.out.println("圆的面积为:\t"+ getArea(radius));
        System.out.println("圆的面积为:\t"+ getCircumstance(radius));
         //或者
        System.out.println("圆的面积为:\t"+ AnyIdeaAplication.getArea(radius));
        System.out.println("圆的面积为:\t"+ AnyIdeaAplication.getCircumstance(radius));

    }

}

第3层次(类的视角)

package com.jd.uos;

public class Circle {
    double radius;

    public Circle() {
        radius=0.0f;
    }

    public Circle(double radius) {
        this.radius = radius;
    }

    public double getRadius() {
        return radius;
    }

    public void setRadius(double radius) {
        this.radius = radius;
    }
    public double getArea(){
        return Math.PI * Math.pow(getRadius(), 2);
    }
    public double getCircumstance(){
        return 2*Math.PI * getRadius();
    }
}

**************************************入口应用程序测试****************************************
package com.jd.uos.test;

import com.jd.uos.Circle;

public class AnyIdeaAplication {
    public static void main(String[] args) {
        Circle myCircle=new Circle();
        System.out.println("圆的半径为:\t"+myCircle.getRadius());
        System.out.println("圆的面积为:\t"+myCircle.getArea());
        System.out.println("圆的周长为:\t"+myCircle.getCircumstance());

        Circle myCircle1=new Circle(10);
        System.out.println("圆的半径为:\t"+myCircle1.getRadius());
        System.out.println("圆的面积为:\t"+myCircle1.getArea());
        System.out.println("圆的周长为:\t"+myCircle1.getCircumstance());


    }
}

第4层次(泛型的视角)

package com.jd.uos;

public class Circle<T> {
    private T radius;

    public Circle() {
    }

    public Circle(T radius) {
        this.radius = radius;
    }

    public T getRadius() {
        return radius;
    }

    public void setRadius(T radius) {
        this.radius = radius;
    }
}


****************************主应用程序测试*************************************

package com.jd.uos.test;

import com.jd.uos.Circle;

public class AnyIdeaAplication {
    public static void main(String[] args) {

        Circle<Double> circle1 = new Circle<Double>(10.12);
        System.out.println("圆的半径为:\t" + circle1.getRadius());
        System.out.println("圆的面积为:\t" + Math.PI * Math.pow(circle1.getRadius(), 2));
        System.out.println("圆的周长为为:\t" + 2 * Math.PI * circle1.getRadius());

        Circle<Integer> circle2 = new Circle<Integer>(12);
        System.out.println("圆的半径为:\t" + circle2.getRadius());
        System.out.println("圆的面积为:\t" + Math.PI * Math.pow(circle2.getRadius(), 2));
        System.out.println("圆的周长为为:\t" + 2 * Math.PI * circle2.getRadius());


    }
}