Can Boolean.valueOf(String) return null?

Question

Can Boolean.valueOf(String) ever return null? From what I can see in the java docs, the docs only specify when it returns true. Is false always returned otherwise, or can null be returned? I have not been able to get it to return null in the tests I have done, but I would like to be sure.

Essentially, I want to know if the following code is safe from a NullPointerException:

boolean b = Boolean.valueOf(...); 

Answer 1

The docs pretty much answer it: no. It'll return a Boolean representing a true or false.

The code is also available:

public static Boolean valueOf(String s) {
    return toBoolean(s) ? TRUE : FALSE;
}

Answer 2

No, this is impossible. See the source code of the class Boolean:

public static Boolean valueOf(String s) {
    return toBoolean(s) ? TRUE : FALSE;
}

.. and then:

private static boolean toBoolean(String name) {
   return ((name != null) && name.equalsIgnoreCase("true"));
}

Answer 3

Actually it could cause NPE but can not return null. Try this:

Boolean bNull = null;
System.print(Boolean.valueOf(bNull)); // -> NPE!

This happens cuz Boolean.valueOf() accepts String or boolean values. Since bNull is of type Boolean java tries to unbox bNull value to pass it as boolean which causes NPE. Its funny but stupid actually... Also there is no Boolean.valueOf() for Number.

Answer 4

No it will not. If null is placed within the argument or if a string is set to null it will return a boolean value of false. You can see expected inputs and outputs in the Java docs: http://docs.oracle.com/javase/7/docs/api/java/lang/Boolean.html#booleanValue()