java.lang.NullPointerException with boolean
I wrote a realy simple code based on another question and here it is:
It throws me an error
java.lang.NullPointerException line 5 and 17
I don't know what I'm doing wrong.
public class Main {
public static String bool(Boolean param){
if(param == true){ (line 5)
return "a";
}else if(param == false){
return "b";
}
return "c";
}
public static void main(String[] args){
System.out.println(bool(true));
System.out.println(bool(null)); (line 17)
System.out.println(bool(false));
}
}
Solution 1:
null
cannot be auto-unboxed to a primitive boolean
value, which is what happens when you try to compare it with true
. In
param == true
The type of true
is boolean
, therefore the left-hand operand must also be a boolean
. You are passing in a Boolean
, which is an object, but can be auto-unboxed to boolean
.
Therefore this is equivalent to
param.booleanValue() == true
Clearly, if param
is null
, the above throws NullPointerException
.
To avoid the hidden pitfalls of auto-unboxing, you could instead work with the Boolean
objects:
if (Boolean.TRUE.equals(param))
return "a";
if (Boolean.FALSE.equals(param))
return "b";
return "c";
Solution 2:
Your code compares a java.lang.Boolean
instance with a primitive boolean
, which means unboxing the java.lang.Boolean
. Since null
can't be unboxed, a NullPointerException
is thrown.
You could work around this by using the built in constants Boolean.TRUE
and Boolean.FALSE
:
public static String bool(Boolean param) {
if (Boolean.TRUE.equals(param)) {
return "a";
} else if (Boolean.FALSE.equals(param)) {
return "b";
}
return "c";
}