包、访问权限、对象的组合

MathApp.java

import geometry.*;
class MathApp{
	public static void main(String args[]){
		Point a=new Point(0,0);
		Point b=new Point(1,1);
		Line line=new Line(a,b);
		double length=line.length();
		System.out.printf("The length of the Line is:"+length);
	}
}

package geometry;

public class Point{
	double x;
	protected double y;
	
	public Point(double x,double y){
		this.x=x;
		this.y=y;
	}
}

package geometry;
public class Line{
	private Point startPoint;
	private Point endPoint;
	
	public Line(Point startPoint,Point endPoint){
		this.startPoint=startPoint;
		this.endPoint=endPoint;
	}
	public double length(){
		double a=startPoint.x-endPoint.x;
		double b=startPoint.y-endPoint.y;
		return Math.sqrt(a*a+b*b);
	}
}

在这个代码的基础上，编写一个程序，该程序能够判断两个圆是否相切。

import geometry.*;
class MathApp{
	public static void main(String args[]){
		Point a=new Point(3,4);
		Point b=new Point(10,4);
		Line line=new Line(a,b);
		double r=3,R=4;
		double d=0;
		d=r+R;
		double length=line.length();
		if(d==length)
		{
			System.out.println("两个圆相切");
		}
		else
		{
			System.out.println("两个圆不相切");
		}
		System.out.printf("The length of the Line is:"+length);
	}
}

package geometry;

public class Point{
	double x;
	protected double y;
	
	public Point(double x,double y){
		this.x=x;
		this.y=y;
	}
}

package geometry;
public class Line{
	private Point startPoint;
	private Point endPoint;
	
	public Line(Point startPoint,Point endPoint){
		this.startPoint=startPoint;
		this.endPoint=endPoint;
	}
	public double length(){
		double a=startPoint.x-endPoint.x;
		double b=startPoint.y-endPoint.y;
		return Math.sqrt(a*a+b*b);
	}
}