本人初学者求高手解释啊这程序哪里出错了？小弟我很费解啊

interface EqualDiagonal { 
 	public void getDiagonal(); 
  
 } 
  
 class Rectangle implements EqualDiagonal { 
 	int a; 
 	int b; 
  
 	public Rectangle(int a, int b) { 
 		this.a = a; 
 		this.b = b; 
 	} 
  
 	public Rectangle(int a) { 
 		this.a = a; 
 		this.b = a; 
 	} 
  
 	public int getchang() { 
 		return a; 
 	} 
  
 	public int getkuan() { 
 		return b; 
 	} 
  
 	public int getzhouchang() { 
 		return (a + b) * 2; 
 	} 
  
 	public int getmianji() { 
 		return a * b; 
 	} 
  
 	public void getDiagonal() { 
 		double s = Math.sqrt((double) (a * a + b * b)); 
 		System.out.println(s); 
 	} 
  
 } 
  
 class Square extends Rectangle implements EqualDiagonal { 
 	public Square(int a) { 
 		super(a); 
 	} 
  
 	public void getDiagonal() { 
 		double s = Math.sqrt((double) (a * a + b * b)); 
 		System.out.println(s); 
 	} 
 } 
  
 public class Main { 
 	public static void main(String[] args) { 
 		Rectangle m = new Rectangle(3, 4); 
 		Square n = new Square(5); 
 		m.getDiagonal(); 
 		n.getDiagonal(); 
  
 	} 
 } 
  
 //result: 
 //5.0 
 //7.0710678118654755

interface EqualDiagonal{    /**     * 求对角线长度     */    public void getDiagonal();}/** * 长方形 */class Rectangle implements EqualDiagonal{    int a;    int b;    public Rectangle(int a, int b)    {        this.a = a;        this.b = b;    }    public int getchang()    {        return a;    }    public int getkuan()    {        return b;    }    public int getzhouchang()    {        return (a + b) * 2;    }    public int getmianji()    {        return a * b;    }    public void getDiagonal()    {        double s = Math.sqrt((double) (a * a + b * b));        System.out.println(s);    }}/** * 正方形 */class Square extends Rectangle{    public Square(int a)    {        super(a, a);    }    public void getDiagonal()    {        double s = Math.sqrt((double) (a * a + b * b));        System.out.println(s);    }}public class Text{    public static void main(String[] args)    {        Rectangle m = new Rectangle(3, 4);        Square n = new Square(5);        m.getDiagonal();        n.getDiagonal();    }}