练习

练习

1.简易计算器

使用静态方法

public class Calculator {
    public static double add(double a,double b){
        return a+b;
    }

    public static double minus(double a,double b){
        return a-b;
    }

    public static double multiply(double a,double b){
        return a*b;
    }

    public static double divide(double a,double b){
        return a/b;
    }

    public static void main(String[] args) {
        System.out.println(Calculator.add(4.4,7.11));
        System.out.println(Calculator.minus(8.9,2.88));
        System.out.println(Calculator.multiply(5.2,13.14));
        System.out.println(Calculator.divide(92,89));
    }
}

2.购买电影票

public class Movie {
    //成员变量
    String name;
    int age;

    //构造方法
    //this关键字
    public Movie(String name,int age){
        this.name=name;
        this.age=age;
    }
    //成员方法
    //18岁以下半价
    public void buy(){
        if(this.age>=18){
            System.out.println(name+"\t\t"+age+"\t\t"+40);
        }else{
            System.out.println(name+"\t\t"+age+"\t\t"+20);
        }
    }

    public static void main(String[] args) {
        System.out.println("姓名\t\t年龄\t\t票价(元)");
        System.out.println("——————————————————————————————————————");

        Movie movie1 = new Movie("李明", 20);
        movie1.buy();//调用以上方法
        Movie movie2 = new Movie("钱丽", 16);
        movie2.buy();
        Movie movie3 = new Movie("周刚", 8);
        movie3.buy();
        Movie movie4 = new Movie("吴红", 32);
        movie4.buy();
    }
}

3.随机输

程序中有红蓝黄三色，运行时随机输出颜色，利用instanceof关键字

class Color{}
class Red extends Color{}
class Yellow extends Color{}
class Blue extends Color{}

public class Demo02 {
    public static void main(String[] args) {
        Color color[]={new Red(),new Yellow(),new Blue()};
        for (int i = 0; i < 3; i++) {
            int index=(int)(Math.random()*3);//数学方法:随机
            judge(color[index]);
        }
    }
    public static void judge(Color color){
        if (color instanceof Red)
            System.out.println("红");
        if (color instanceof Yellow)
            System.out.println("黄");
        if (color instanceof Blue)
            System.out.println("蓝");
    }
}