Null Pointer Access Warning

Question

A part of the code I made should have looked like this.

String name = request.getParameter("Name");
if(name!=null && !name.isEmpty())
{
    DO SOMETHING
}

But ended up using '||' operator rather than '&&' operator. And i was given a warning at

name .isEmpty()

saying

Null Pointer Access: The variable name can only be null at this location.

Can somebody explain me why that happened?

And by the way, ' request ' is a HttpServletRequest Object that i get from a previous class.

Answer 1

name != null || !name.isEmpty()

1. If name is not null, the second condition is never checked;
2. if name is null, the second condition is checked and throws a NullPointerException .

Answer 2

When you do:

if(name!=null || !name.isEmpty())

Then if the second part is reached, name is null due to Short-circuit evaluation .

Remember that false && anything is false and true || anything true || anything is true .

Answer 3

You can do:

String name = request.getParameter("Name") != null ? request.getParameter("Name") : "";

to ensure that name is not null . And then

if (name.isEmpty()) { ... }

Answer 4

if(name!=null ){
   if(!name.isEmpty()){
       //body
   }
}