Comparing two different objects for being the same values

Question

I have two objects of type MyObject. Their private fields have things like Integer, int, Long, long, String, etc -- no fancy sub-objects or anything to this effect.

I want to check to see if their fields are equal. I am not trying to check if they are the same object in memory (the same reference?), which they shouldn't be anyway since these two objects are from separate lists / created separately.

What is the correct way to check if all the fields of one object have the same values as all the other fields of the second object?

• Zircon: I don't really understand what the problem you're facing is. Do you feel you have "too many" fields for overriding .equals?
• Kayaman: Override the boolean equals(Object o) method.
• AJJ: @Zircon I just want to make sure overriding .equals is the correct thing to do here, as opposed to doing object1 == object2 or object1.equals(object2) or implementing Comparable or Comparator or something. Too many options and I am unsure which is correct.

Answer 1

The best way is to override the method equals(Object) and let your IDE implements it for you.

• AJJ: My IDE doesn't seem to have a way to implement it for me? (Android Studio). I just wrote @Override onpublic boolean equals(Object obj), checked if obj was an instance of myObject, typecasted it, and then returned a big and-chain of field comparisons. Is this all I have to do?
• Nicolas Filotto: provide your class definition with your fields in your question and your java version, I will generate it for you
• AJJ: I do see a generate function in Android Studio actually but I don't know which Template to use(IntelliJ Default, Apache commons-lang, Apache commons-lang 3, Objects.equal and hashCode (Guava), java.util.Objects.equals and hashCode (java 7+)).
• Nicolas Filotto: choose IntelliJ for example
• Nicolas Filotto: or if you use java 8, you can use java.util.Objects.equals and hashCode (java 7+)

Answer 2

You need to override the equal method in your class and compare if the values of the two class are same return true else false. example:

obj1.equals(obj2);

in your class

@Override
public boolean equals(YourClass obj) {
 // compare the values of both objets.
 // return true on success;
}

Answer 3

Use Object.equals() to compare

Answer 4

Overriding Object's equals method is the best choice for your situation. You can either ensure the equality of every field of the object, or you can just compare a field or combination of fields that you know will be unique.

If you're using collections such as Maps, you might consider overriding hashcode using these fields instead, and then compare hashcodes in the equals method.

For your reference:

• equals should always determine if two objects are "equal" in concept (which usually means they have the same fields).
• == compares memory location, and thus equality between primitive types
• Comparable interface is used to order an object "ahead" or "behind" another object; useful for sorting arrays and collections.
• Comparator interface is similar to Comparable but uses a "third-party" object to compare two other objects. This Comparator can be passed into collection-sorting methods if you don't want your objects to be Comparable.

Answer 5

mDo as @Raj K suggested. For example, if you have:

public class MyObject {
 int i1;
 long l1;
 long i2;
 // and a bunch of c'tors and methods
}

then your equals() method would be something like

public Boolean equals( Object o ) {
 if ( o instanceof MyObject ) {
 MyObject m = (MyObject)o;
 return (i1==m.i1) && (l1==m.l1) && (l2==m.l2);
 }
 return false;
}

If any of your fields are Objects, you have to be a bit more careful, since you also have to first check for null's before checking whether

this.something.equals(m.something)