Question

I know that the HashSet.contains() method uses the .equals method to check equality as in it checks the pointer to see whether they’re equal.

I need it to check the actual object at the pointer for equality – in my specific case, I need to see whether a “Node” being opened (an int[] array) already exists in the HashSet. This is essential for my search algorithm so that the implementation of my Bi-directional Iterative Deepening Search isn’t as naive.

I’d still like linear search time if possible, or perhaps I should use a different class?

Thanks for your help.

Answer 1

Reference equality is just the default implementation of .equals(). You can put your arrays in a wrapper class that overrides equals and hashCode to check the contents. NB: In order for this to work the contents must not change after you put them in the set.

import java.util.Arrays;

public class IntArrayNode {

private int[] array;

public IntArrayNode(int[] array) {
  this.array = array;
}

//getter and setter

public boolean equals(Object obj) {
  if (obj != null && obj instanceof IntArrayNode) {
    return Arrays.equals(this.array, ((IntArrayNode) obj).array);
  } else {
    return false;
  }
}

public int hashCode() {
  return Arrays.hashCode(this.array);
}
}