Java学习第43天2020/8/17

一.

import java.util.Scanner;
class dis{
public void distance(double a,double b,double m,double n)
{
	System.out.println("两点之间的距离为："+Math.sqrt((a-m)*(a-m)+(b-n)*(b-n)));
}
}
public class Pointa {
	double  a,b;
	public void set(double k,double f)
	{
		a=k;
		b=f;
	}
	public double get_a()
	{
		return a;
	}
	public double get_b()
	{
		return b;
	}
     public static void main(String []args)
     {
    	 Pointa []k=new Pointa[2];
    	 Scanner input=new Scanner(System.in);
    	 double []l=new double[4];
    	 for(int i=0;i<4;i++)
    	 {
    		 l[i]=input.nextDouble();
    	 }
    	 k[0]=new Pointa();
    	 k[1]=new Pointa();
    	 k[0].set(l[0],l[1]);
    	 k[1].set(l[2],l[3]);
    	 dis o=new dis();
    	 o.distance(k[0].get_a(), k[0].get_b(), k[1].get_a(), k[1].get_b());
     }
}

 

 java中没有友元的概念

//Test1.java

package test;

class Test1 {}

//Test2.java

package test;

public class Test2 {
public static void main(String[] args) {
Test1 t;
}
}

二.在class中使用本类未成功

三.例题