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.

If you don't like extra null checks:

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

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) { ... }

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.

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

Optional.ofNullable(boolValue).orElse(false)

:)

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

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

Boolean is the object wrapper class for the primitive boolean. This class, as any class, can indeed be null. For performance and memory reasons it is always best to use the primitive.

The wrapper classes in the Java API serve two primary purposes:

1. To provide a mechanism to “wrap” primitive values in an object so that the primitives can be included in activities reserved for objects, like as being added to Collections, or returned from a method with an object return value.
2. To provide an assortment of utility functions for primitives. Most of these functions are related to various conversions: converting primitives to and from String objects, and converting primitives and String objects to and from different bases (or radix), such as binary, octal, and hexadecimal.

http://en.wikipedia.org/wiki/Primitive_wrapper_class

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.

if (bool) will be compiled as if (bool.booleanValue()) and that would throw a NPE if bool is null.

Other solutions for nullable boxed Boolean evaluation:

• JDK 9+

  import static java.util.Objects.requireNonNullElse;
  
  if (requireNonNullElse(bool, false)) {
      // DoSomething
  

• Google Guava 18+

  import static com.google.common.base.MoreObjects.firstNonNull;
  
  if (firstNonNull(bool, false)) {
      // DoSomething
  

false is used for the null-case here.

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.