Compare two Java objects with a check for null

Question

I feel like such a novice for asking this question, but is there a method in the JDK that compares two objects for equality, accounting for nulls? Something like this:

public static boolean equals(Object o1, Object o2)
{
    if (o1 == null)
    {
        return o2 == null; // Two nulls are considered equal
    }
    else if (o2 == null)
    {
        return false;
    }

    return o1.equals(o2);
}

It seems silly to write this method myself since I would think that it has to exist already somewhere.

Update: Removed the generics (type parameter) since it did not add any value in this case.

Answer 1

If you are worried about NullPointerExceptions you could just test equality like:

if (obj1 != null && obj1.equals(obj2)) { ... }

The general contract of equals() is that a non-null object should never be equal to a null reference, and that the equals() method should return false if you are comparing an object to a null reference (and not throw a NPE).

Answer 2

Apache Commons Lang has such a method. You don't want generics on such a method, it will lead to bogus compilation errors, at least in general use. Equals knows very well (or should - it is part of the contract) to check the class of the object and return false, so it doesn't need any additional type safety.

Answer 3

Whenever I come across a need and think "this is so common Java must have it" but find it doesn't, I check the Jakarta Commons project. It almost always has it. A quick search of the commons-lang API (which has the most basic of common utilities) shows an equals() method that provides what you want.

Answer 4

As far as I have seen (in java, c# etc.) you usually use equals in the manner: obj1.equals(obj2) and not SomeLibrary.equals(obj1, obj2)

This is because it is much more scalable for a language and library to rely on an object to know if it equals another object. (as you use obj1.equals anyway) and most of the time if you don't have something to compare to you're in pretty big trouble.

Matt's answer is the best format in my opinion because it doesn't requre another library method call (for what it's worth) and is still intent revealing.

Answer 5

Jakarta Commons Lang API has what you are looking for ObjectUtils.equals(Object,Object)