java学习51天2020/8/25

import java.util.Scanner;
public class Circle {
     private double radius; //半径
     public Circle() {
     }
     public Circle(double radius) {
         this.radius = radius;
     }
     public void getArea() {
         double s;
         s=3.1415926*radius*radius;
         System.out.printf("面积：%-10f",s);
     }
     public static void main(String[] args) {
         Scanner in=new Scanner(System.in);
        double r;
         System.out.print("半径：");
         r=in.nextDouble();
         Circle c=new Circle(r);
         c.getArea();
     }
 }

 

 

 

 import java.util.Scanner;

 public class Tree {
    private int ages; //树龄
     public Tree() {
    }
    public Tree(int ages) {
    	this.ages=ages;
    }
     public void grow(int years) {
         ages+=years;
     }
     public void age() {
         System.out.println("树龄："+ages);
     }
     public static void main(String[] args) {
         Scanner in=new Scanner(System.in);
         int a,b;
         System.out.print("请输入原有树龄：");
         a=in.nextInt();
         System.out.print("请输入生长的年数：");
         b=in.nextInt();
         Tree t=new Tree(a);
         t.grow(b);
         t.age();
     }
 }

 

 

二

三.例题