CODEWITHSUNDEEP
java
Birdman
Birdman

Reputation: 5414

Check if null Boolean is true results in exception

I have the following code:

Boolean bool = null;

try 
{
    if (bool)
    {
        //DoSomething
    }                   
} 
catch (Exception e) 
{
    System.out.println(e.getMessage());             
}

Why does my check up on the Boolean variable "bool" result in an exception? Shouldn't it just jump right past the if statement when it "sees" that it isn't true? When I remove the if statement or check up on if it's NOT null, the exception goes away.

Upvotes: 245

Views: 341876

Answers (8)

bjmi
bjmi

Reputation: 603

if (bool) will be compiled to if (bool.booleanValue()) aka unboxing and that would throw a NullPointerException if bool is null.

Other solutions for nullable boxed Boolean evaluation:

false is used as the default for the null-case here.

Upvotes: 2

Anonymous
Anonymous

Reputation: 86276

Objects.equals()

There is nothing wrong with the accepted answer by K-ballo. If you prefer a single simple condition and like me you don’t like Yoda conditions, since java 1.7 the answer is

    if (Objects.equals(bool, true)) {

or if at the same time you prefer to be really explicit

    if (Objects.equals(bool, Boolean.TRUE)) {

Or better: avoid the issue

It’s not recommended to use Boolean objects thereby allowing a Boolean reference to be null in the first place. The risk of a NullPointerException like the one you saw is too great. If you need a kind of tri-state logic, it’s better to define an enum with three values. For example

enum MyTristateBoolean { FALSE, DONT_KNOW, TRUE }

Now we don’t need null at all. The middle constant should probably be named UNKNOWN, UNDEFINED, NOT_EXISTING or something else depending on your exact situation. You may even name it NULL if appropriate. Now depending on taste your comparison becomes one of the following two.

    if (myBool.equals(MyTristateBoolean.TRUE)) {

    if (myBool == MyTristateBoolean.TRUE) {

The latter works since the compiler guarantees that you will only have one instance of each enum constant. As most of you know == doesn’t work for comparing objects of non-enum type for equality.

Upvotes: 5

provisota
provisota

Reputation: 1660

Or with the power of Java 8 Optional, you also can do such trick:

Optional.ofNullable(boolValue).orElse(false)

:)

Upvotes: 41

Joshua Pinter
Joshua Pinter

Reputation: 47481

Use the Apache BooleanUtils.

(If peak performance is the most important priority in your project then look at one of the other answers for a native solution that doesn't require including an external library.)

Don't reinvent the wheel. Leverage what's already been built and use isTrue(): 

BooleanUtils.isTrue( bool );

Checks if a Boolean value is true, handling null by returning false.

If you're not limited to the libraries you're "allowed" to include, there are a bunch of great helper functions for all sorts of use-cases, including Booleans and Strings. I suggest you peruse the various Apache libraries and see what they already offer.

Upvotes: 116

fastcodejava
fastcodejava

Reputation: 41097

Boolean types can be null. You need to do a null check as you have set it to null. 

if (bool != null && bool)
{
  //DoSomething
}

Upvotes: 19

AvrDragon
AvrDragon

Reputation: 7479

If you don't like extra null checks:

if (Boolean.TRUE.equals(value)) {...}

Upvotes: 593

K-ballo
K-ballo

Reputation: 81349

When you have a boolean it can be either true or false. Yet when you have a Boolean it can be either Boolean.TRUE, Boolean.FALSE or null as any other object.

In your particular case, your Boolean is null and the if statement triggers an implicit conversion to boolean that produces the NullPointerException. You may need instead:

if(bool != null && bool) { ... }

Upvotes: 211

RicardoE
RicardoE

Reputation: 1725

as your variable bool is pointing to a null, you will always get a NullPointerException, you need to initialize the variable first somewhere with a not null value, and then modify it.

Upvotes: 1

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