java - 如何使 java HashSet/HashMap 与任何对象一起工作？

Question

是否可以使 HashSet 与任何对象一起工作？我试图让对象实现可以比较，但没有帮助

import java.util.HashSet;
public class TestHashSet {
    public static void main(String[] args) {
        class Triple {
            int a, b, c;

            Triple(int aa, int bb, int cc) {
                a = aa;
                b = bb;
                c = cc;
            }
        }
        HashSet<Triple> H = new HashSet<Triple>();
        H.add(new Triple(1, 2, 3));
        System.out.println(H.contains(new Triple(1, 2, 3)));//Output is false
    }
}

Answer 1

您需要实现equals(Object)和 hashCode()

确保对象相等时哈希码也相等

在您的示例中:

class Triple {
    int a, b, c;

    Triple(int aa, int bb, int cc) {
        a = aa;
        b = bb;
        c = cc;
    }

    public boolean equals(Object arg){
        if(this==arg)return true;
        if(arg==null)return false;
        if(arg instanceof Triple){
            Triple other = (Triple)arg;
            return this.a==other.a && this.b==other.b && this.c==other.c;
        }
        return false;
    }

    public int hashCode(){
      int res=5;
      res = res*17 + a;
      res = res*17 + b;
      res = res*17 + c;
      //any other combination is valid as long as it includes only constants, a, b and c

      return res;
    }

}