Boolean Object and boolean variable issue in JAVA

Question

I declare a Boolean variable. For example Boolean dataVal=null;
Now if I execute the following code segment:

if(dataVal)
    System.out.println("\n\NULL value in dataVal: "+dataVal);
else
    System.out.println("\n\nvalue in dataVal: "+dataVal);

I get NullPointerException. Well, I know its obvious, but I need to know the reason behind this.

@Russell - `Boolean` is an object, not a primitive, ergo null makes sense. — mcfinnigan, Feb 28 '12 at 10:20

score 39 · Accepted Answer · answered Feb 28 '12 at 10:00

When you evaluate the boolean value of a Boolean object Java unbox the value (autoboxing feature, since 1.5). So the real code is: dataVal.booleanValue(). Then it throws NullPointerException. With any boxed value, unboxing a null object throws this exception.

Before 1.5 you had to unbox the value by hand: if (dataVal.booleanValue()) so it was more evident (more verbose too :)

score 16 · Answer 2 · answered Feb 28 '12 at 10:00

16

Because dataVal is being casted to boolean using Boolean.booleanValue() which gets translated to null.booleanValue() which leads you to a NullPointerException.

answered Feb 28 '12 at 10:00

Alex

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Jerome · Answer 3 · 2012-02-28T10:36:30.113

You can have a look at the specification for unboxing issues, your situation is described here section 5.1.8 Unboxing Conversion : If r is null, unboxing conversion throws a NullPointerException

That means your if ( /* Boolean object */ ) will never be unboxed into a boolean primitive type and therefore throw a NPE because you are doing an invalid if(null).

By the way, unboxing will work if you had:

final Boolean booleanTest = new Boolean (true);
if (booleanTest) {
    // Do something
}

score 1 · Answer 4 · answered Feb 28 '12 at 10:00

1

Boolean (class) != boolean (primitive type).

Java tries to get the primitive value calling dataVal.booleanValue(). Because dataVal is null, you get a null pointer exception.

answered Feb 28 '12 at 10:00

Pablo

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score 0 · Answer 5 · answered May 21 '18 at 21:23

0

When you try to evaluate Boolean object value jvm internally call booleanValue() on that object as you assign null to that object it will throw NullPointerException

answered May 21 '18 at 21:23

Rakesh Bhagat

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score 0 · Answer 6 · answered Mar 31 '22 at 21:24

0

use BooleanUtils.tobolean(?), it returns false if the passed param is null

answered Mar 31 '22 at 21:24

Said Dekkaki

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This doesn't answer the question at all - why exactly the NPE occurs. You answered the question how to prevent it, but the OP didn't ask this. – cyberbrain Apr 03 '22 at 18:34

score 0 · Answer 7 · answered Feb 28 '12 at 10:00

0

if(null) is not a valid expression, simple as that.

Under the hoods, the VM is using auto-boxing... so you get a NullPointerException.

answered Feb 28 '12 at 10:00

Marcelo

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Boolean Object and boolean variable issue in JAVA

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