通過繼承Rect類編寫一個具有確定位置的矩形類PlainRect，其確定位置用 矩形的左上角坐標來標識，包含： 添加兩個屬性：矩形左上角坐標startX和startY。 兩個構造方法： 帶4個參數的構造方法，用於對startX、startY、width和height屬性 初始化； 不帶參數的構造方法，將矩形初始化為左上角坐標、長和寬都為0 的矩形； 添加一個方法： 判斷某個點是否在矩形內部的方法

package b;

public class Rect {
    Double width;
    Double height;
    public Double getWidth() {
        return width;
    }
    public void setWidth(Double width) {
        this.width = width;
    }
    public Double getHeight() {
        return height;
    }
    public void setHeight(Double height) {
        this.height = height;
    }
    public Rect(Double width, Double height) {
        super();
        this.width = width;
        this.height = height;
    }
    Rect()
    {
        width=10.0;
        height=10.0;    
    }
    
    public void area()
    {
        if(width<0||height<0)
        {
            System.out.println("數據錯誤");
        }
        else
        System.out.println("矩形的面積為 width*height="+(width*height));
    }
    public void perimeter()
    {
        if(width<0||height<0)
        {
            System.out.println("數據錯誤");
        }
        else
        System.out.println("矩形的周長為 2*(width+height)="+(2*(width+height)));
    }
}

public class PlainRect extends Rect {
    private double startX;
    private double startY;
    public double getStartX() {
        return startX;
    }
    public void setStartX(double startX) {
        this.startX = startX;
    }
    public double getStartY() {
        return startY;
    }
    public void setStartY(double startY) {
        this.startY = startY;
    }
    public PlainRect(Double width, Double height, double startX, double startY) {
        super(width, height);
        this.startX = startX;
        this.startY = startY;
    }
    PlainRect()
    {
        width=0.0;
        height=0.0;
        startX=0.0;
        startY=0.0;                
    }
    boolean isInside(double x,double y)
    {
        if(x>=startX&&x<=(startX+width)&&y<startY&&y>=(startY-height))
        {
            
            System.out.println("("+x+","+y+")在矩形內");
            return true;
        }
        else
        {
            System.out.println("("+x+","+y+")不在矩形內");
            return false;
        }
    }
    

}

package b;

public class TestRect {

    public static void main(String[] args) {
        PlainRect juxing=new PlainRect();
        juxing.setWidth(10.0);
        juxing.setHeight(20.0);
        juxing.area();
        juxing.perimeter();
        juxing.setStartX(10);
        juxing.setStartY(10);
        juxing.isInside(25.5, 13);
        

    }

}