How to rewrite the equals method

Question

I saw a colleague write it as follows:

 @Override
 public boolean equals(Object obj) {
    if (this == obj) {
        return true;
    }
    if (obj == null) {
        return false;
    }
    if (getClass() != obj.getClass()) {
        return false;
    }
    final ImageCode other = (ImageCode) obj;
    if ((this.code == null) ? (other.code != null) : !this.code.equals(other.code)) {
        return false;
    }
    return true;
}

Then, I suggested changing it for this:

@Override
public boolean equals(Object obj) {
    if (this == obj) {
         return true;
    }
    if (!(obj instanceof Parent)){
         return false;
    }
    final ImageCode other = (ImageCode) obj;
    if ((this.code == null) ? (other.code != null) : !this.code.equals(other.code)) {
         return false;
    }
    return true;
 }

but he told me that it is wrong, and that instanceof can't be used for the equals method. I don't understand why he said that.

Can't say. Have you tried to run your equals override with some debug lines? — Hooch, Jun 23 '16 at 09:05
Class C extends B. And B extends A. Then object c is instanceof C(or B or A). Doesn't mean c and b(or a) is the same class. — waltersu, Jun 23 '16 at 09:05
@Hooch,@waltersu ,but i have tested for extending,i could't found any error. — lucare, Jun 23 '16 at 09:13

score 2 · Accepted Answer · answered Jun 23 '16 at 09:08

You can use instanceof in equals. Java uses it all the time. See e.g. String

public boolean equals(Object anObject) {
    if (this == anObject) {
        return true;
    }
    if (anObject instanceof String) {
        String anotherString = (String)anObject;

        // More code ...
        return true;
    }
    return false;
}

score 0 · Answer 2 · answered Jun 23 '16 at 09:25

@dejvuth, If anObject is instance of String then why do we need to typecast. You can directly use it. I think its ok to go ahead without checking instanceOf. Just you may need to type cast the object. You can check my code here.

http://www.javavni.com/is-hashcode---and-equals---required-together.html

How to rewrite the equals method

2 Answers2