按要求编写一个Java应用程序：编写一个矩形类

package Text5;

public class Text5 {

public static void main(String[] args) {
	// TODO Auto-generated method stub
	PlainRect ljt = new PlainRect();
	Rect ml = new Rect();
	ljt.showxy(20, 10, 10, 10);
	ml.area();
	ml.perimeter();
	ljt.isInside(25.5, 13);
}

}

package Text5;

//矩形类
public class Rect {
public double length = 10; //长
public double width = 10; //宽

public void show(double length, double width) {
	this.length = length;
	this.width = width;
}

public void area() {
	double sum;
	sum = width * length;
	System.out.println("面积为： " + sum);
}

public void perimeter() {
	double sum;
	sum = (width + length) * 2;
	System.out.println("周长为："  + sum);
}

}

package Text5;

public class PlainRect extends Rect{
public double startx;
public double starty;

public void showxy(double length, double width, double startx, double starty) {
	System.out.println("请分别输入长，宽，x与y：");
	this.length = length;
	this.width = width;
	this.startx = startx;
	this.starty = starty;
	System.out.println("长为：" + length + "宽为：" + width);
	System.out.println("x为：" + startx + "y为：" + starty);
}

public void isInside(double x, double y) {
	if (x  >= startx && x <= (startx + width) && y < starty && y >= (starty-width))
		System.out.println("在！");
	else
		System.out.println("不在！");
}

}