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up vote 2 down vote favorite

What's the difference between these two code snippets?

Snippet 1:

Object o = new Object();
int i = Objects.hashCode(o);

Snippet 2:

Object o = new Object();
int i = o.hashCode();
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java.util.Objects since 1.7. – 卢声远 Shengyuan Lu Apr 24 at 8:52

4 Answers

up vote 7 down vote accepted

The only difference is that if o is null, Objects.hashCode(o) returns 0 whereas o.hashCode() would throw a NullPointerException.

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Objects is a class with hashCode being a static method in it. – Arjun Rao Apr 24 at 8:50
2  
@downvoter: Please explain. – Arjun Rao Apr 24 at 8:50
@Apurv See here (since 1.7). – Dukeling Apr 24 at 8:52
@ArjunRao: So, assuming there are no null objects, they're just the same? – MC Emperor Apr 24 at 9:13
No since Objects.hashCode(o) has an additional logic to determine if o is null. If you're sure o is not null, it is marginally (negligibly) better to use o.hashCode(). – Arjun Rao Apr 24 at 9:14
up vote 0 down vote 
Object o = new Object();
int i = Objects.hashCode(o);

It returns the hash code of a not-null argument and 0 for null argument. This case it is Object referred by o.It doesn't throw NullPointerException.

Object o = new Object();
int i = o.hashCode();

Returns the hashCode() of Object referred by o. If o is null , then you will get a NullPointerException.

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up vote 2 down vote 
java.util.Objects {
    public static int hashCode(Object o) {
        return o != null ? o.hashCode() : 0;
    }
}

This is a NPE safe alternative to o.hashCode().

No difference otherwise.

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up vote 4 down vote

This is how Objects.hashCode() is implemented:

public static int hashCode(Object o) {
    return o != null ? o.hashCode() : 0;
}

If o is null then Objects.hashCode(o); will return 0, whereas o.hashCode() will throw a NullPointerException.

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