java - PriorityQueue add Element will change the element, weird bug -

public class main {     public static class ee implements comparable<ee> {         int x;         int[] rac;         public  ee(int x, int[] rac) {             this.x = x;             this.rac = rac;         }          public int compareto(ee that) {             if (this.x != that.x) return this.x - that.x;             else return this.rac[2] = that.rac[2];         }     }  public static void main(string[] args) {         int [][] ary = {                 {1,1,3,3},                  {1,3,2,4},                 {2,3,3,4}};         priorityqueue<ee> pq = new priorityqueue<ee>();         (int[] rec : ary) {             ee e1 = new ee(rec[0], rec);             ee e2 = new ee(rec[2], rec);             pq.add(e1);             pq.add(e2);         }     } 

this piece of code i'm running, fine when second loop entered, rec [1, 3, 2, 4] initially, when pq.add(e1) called, value of rec become [1, 3, 3, 4] can explain why happens? thank in advance!

the preoblem in comapreto method:

return this.rac[2] = that.rac[2]; 

it's returning latter that.rac[2]. should be:

return this.rac[2] == that.rac[2];