java新手，有个简单的问题
正方形继承长方形，哪里出问题了
class Rectangle{
private int x1;
private int x2;
private int y1;
private int y2;

public Rectangle(int x1,int x2,int y1,int y2){
this.x1=x1;
this.x2=x2;
this.y1=y1;
this.y2=y2;
}
public int getHeight(){
int aHeight=0;
aHeight=Math.abs(x1-x2);
return aHeight;
}
public int getWidth(){
int aWidth=0;
aWidth=Math.abs(y1-y2);
return aWidth;
}
public int getPerimeter(){
int aPerimeter=0;
aPerimeter=getHeight()*2+getWidth()*2;
return aPerimeter;
}
public int getArea(){
int aArea=0;
aArea=getHeight()*getWidth();
return aArea;
}
}

class Triangle{
private int x1;
private int y1;
private int x2;
private int y2;
private int x3;
private int y3;

public Triangle(int x1,int x2,int x3,int y1,int

y2,int y3){
this.x1=x1;
this.y1=y1;
this.x2=x2;
this.y2=y2;
this.x3=x3;
this.y3=y3;
}
public double getFirstLength(){
double aFirstLength=0;
aFirstLength=Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)

*(y1-y2));
return aFirstLength;
}
public double getSecondLength(){
double aSecondLength=0;
aSecondLength=Math.sqrt((x2-x3)*(x2-x3)+(y2-

y3)*(y2-y3));
return aSecondLength;
}
public double getThirdLength(){
double aThirdLength=0;
aThirdLength=Math.sqrt((x1-x3)*(x1-x3)+(y1-y3)

*(y1-y3));
return aThirdLength;
}
public double getPerimeter(){
double aPerimeter=0;
aPerimeter=getFirstLength()+getSecondLength

()+getThirdLength();
return aPerimeter;
}
public double getArea(){
double aArea=0;
double half=getPerimeter()/2;
aArea=Math.sqrt(half*(half-getFirstLength())*
(half-getSecondLength())*(half-

getThirdLength()));
return aArea;
}
}

class Circle{
private int x1;
private int y1;
private int r;
private double constant;

public Circle(int x1,int y1,int r){
this.x1=x1;
this.y1=y1;
this.r=r;
constant=3.1415;
}
public int getDiameter(){
int aDiameter=0;
aDiameter=2*r;
return aDiameter;
}
public double getPerimeter(){
double aPerimeter=0;
aPerimeter=constant*getDiameter();
return aPerimeter;
}
public double getArea(){
double aArea=0;
aArea=constant*r*r;
return aArea;
}
}

class LineSegment{
private int x1;
private int y1;
private int x2;
private int y2;

public LineSegment(int x1,int y1,int x2,int y2){
this.x1=x1;
this.y1=y1;
this.x2=x2;
this.y2=y2;
}
public double getLineLength(){
double aLineLength=0.0;
aLineLength=Math.sqrt((x1-x2)*(x1-x2)+(y1-

y2)+(y1-y2));
return aLineLength;
}
}

class Square extends Rectangle{


public Square(int x1,int x2,int y1,int y2){

super(x1,x2,y1,y2);
this.x2=x1
this.y2=y1;

}
public int getPerimeter(){
return super.getPerimeter();
}
public int getArea(){
return super.getArea();
}

}
public class PassTest1{
public static void main(String[] args){
Square a=new Square(10,20,30,40);
LineSegment e=new LineSegment(0,0,10,20);
Rectangle t=new Rectangle(10,10,30,30);
Triangle s=new Triangle(0,0,0,20,10,10);
Circle c=new Circle(10,10,5);

System.out.println(t.getPerimeter());
System.out.println(c.getPerimeter());
System.out.println(s.getPerimeter());
System.out.println(a.getPerimeter());
System.out.println(t.getArea());
System.out.println(c.getArea());
System.out.println(s.getArea());
System.out.println(a.getArea());

}
}

[解决办法]
其实正方形可以加一个只有两个参数的构造器，

像你现在的Square a=new Square(10,20,30,40);

第一和第三参数都没有什么用。。。