Java Object equals

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Object.equals

    public static void main(String[] args) {
        Test t = new Test("hi");
        Test t2 = new Test("hi");
        t.equals(t2);
    }
    
    static class Test {
      String test;

      Test(String test) {
          this.test = test;
      }
    }

Every object’s ancestor is Object, and Object has an equals method.

If you create an object and don’t override equals yourself,

    public boolean equals(Object obj) {
        return (this == obj);
    }

it behaves as shown above—an equals that only returns true when the reference addresses are the same.

    String t3 = "hi";
    String t4 = "hi";
    t3.equals(t4);
   
    Long t5 = 5L;
    Long t6 = 5L;
    t5.equals(t6);

String’s equals looks like this:

    public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        return (anObject instanceof String aString)
                && (!COMPACT_STRINGS || this.coder == aString.coder)
                && StringLatin1.equals(value, aString.value);
    }

And Long’s equals looks like this:

    public boolean equals(Object obj) {
        if (obj instanceof Long) {
            return value == ((Long)obj).longValue();
        }
        return false;
    }

Wrapper classes override equals to compare values instead of the reference address we might otherwise expect.

Conclusion

If you want to compare values rather than reference addresses, using a wrapper class’s equals is the right approach.