java.lang.ClassCastException in Arrays.sort call though implementing Comparable -

i trying sort array of rectangles using arrays.sort. class rectangle implements comparable<rectangle> , have overridden compareto() method. these 2 classes: rectangle , tester class.

public class rectangle implements comparable<rectangle> {    private int length;   private int width;    public rectangle(int length, int width) {     this.length = length;     this.width = width;   }    public int getlength() {     return length;   }    public int getwidth() {     return width;   }    public int getperimeter() {     return (2*length) + (2*width);   }    public int compareto(rectangle x) {     int p2 = ((rectangle)x).getperimeter();     return this.getperimeter()-p2;   }    public string tostring() {     return "perimeter: " + this.getperimeter();   } } 

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import java.util.*; public class test {  public static void main(string[] args) {    rectangle[] rectangles = new rectangle[4];   rectangles[0] = new rectangle(3, 4);   rectangles[1] = new rectangle(2, 6);   rectangles[2] = new rectangle(2, 2);   rectangles[3] = new rectangle(1, 1);    (rectangle x : rectangles) {     system.out.println(x.getperimeter());   }    arrays.sort(rectangles); } 

however, keep getting error message:

exception in thread "main" java.lang.classcastexception: rectangle cannot cast java.lang.comparable.

can me see i'm doing wrong?

exception in thread "main" java.lang.classcastexception: rectangle cannot cast java.lang.comparable. 

possibly version of rectangle in main class not comparable. make sure class rectagle refering 1 shown above.

make sure build class correctly. suggest using ide build classes , doing clean build should fix this.