Alternative to object.equals(null) in java

Question

Please help me with these java syntax issue.

I know obj.equals(null) is wrong, so whats the correct way to write an expression like

 if(!obj.equals(null)){
 some code    
}

I am confused between option 1

if(!(obj == null)){
some code
}

and the other option 2

if(obj != null){
some code
}

There's one more, for an expression like

    if(obj.equals(null) || obj2.equals(obj3))

am I correct if I write

if(obj == null || obj2.equals(obj3))

or should this be different ?

[Here's](http://stackoverflow.com/a/4501084/645270) some info — keyser, Aug 08 '13 at 13:52
option 1 is option 2. If `obj` is `null`, `obj.equals(null)` will throw a `NullPointerException`, and `obj == null` simply evalute to `true`. — johnchen902, Aug 08 '13 at 13:52
Both options 1 and 2 work ok, 2 being more common. The last code line looks fine. — kiheru, Aug 08 '13 at 13:52
Seriously, you are wondering whether `!(A==B)` and `(A!=B)` are equivalent? — fvu, Aug 08 '13 at 13:53
Don't do option 1. It's technically correct, but uuuugly. It's about as close to objectively wrong as an issue of style can be. — yshavit, Aug 08 '13 at 13:54

Diego Urenia · Answer 1 · 2013-08-08T13:56:52.587

1

As you are verifying whether the reference is null or not, then use this:

if(obj != null){
}

or

if(!(obj == null)){
}

edited Aug 08 '13 at 13:56

answered Aug 08 '13 at 13:50

Diego Urenia

score 1 · Answer 2 · answered Aug 08 '13 at 13:52

1

Options 1 and 2 are logically equivalent. I'd prefer Option 2, it's more concise.

if(obj == null || obj2.equals(obj3)) is best because you avoid the possibility of calling a function on a null object.

answered Aug 08 '13 at 13:52

Kukanani

rocketboy · Answer 3 · 2013-08-08T13:56:37.557

0

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

thats the actual Object#equals implementation. They all are logically equivalent.

Except that if calling Object object is null, object.equals() will throw an NPE.

edited Aug 08 '13 at 13:56

answered Aug 08 '13 at 13:50

rocketboy

score 0 · Accepted Answer · answered Aug 08 '13 at 13:52

These are logically equivalent, meaning they will resolve the same way:

if(!(obj == null)){
    //some code
}


if(obj != null){
   //some code
}

If the object is null, this will result in a null pointer exception:

if(obj.equals(null) || obj2.equals(obj3))

This say if an object is null or if obj2 equals obj3, then execute a block of code.

if(obj == null || obj2.equals(obj3))

4 Answers4