Why Does Checking a Null Boolean Result in an Exception?

Why am I encountering an exception when checking a null Boolean value in my Java code?

Boolean bool = null;

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

In Java, a Boolean variable that is null cannot be directly evaluated in a boolean expression. Attempting to do so results in a NullPointerException. This is explained in the following breakdown of the issue and suggested solutions to avoid this error.

Boolean bool = null;

// Safe check for null before evaluating
if (bool != null && bool) {
    // DoSomething
} else {
    // Handle the case when bool is null or false
}

Causes

• The Boolean variable 'bool' is initialized to null.
• In Java, null values cannot be treated as Boolean when evaluated. When the expression 'if (bool)' is executed, it tries to dereference a null value, leading to a NullPointerException.

Solutions

• Check if the Boolean variable is not null before using it in a conditional statement. For example: if (bool != null && bool) { // Execute code only if bool is true }
• Use the Boolean wrapper class's static method to handle potential nulls safely, such as Boolean.TRUE.equals(bool). This returns true only if a Boolean is not null and equals true.

Mistake: Directly checking a null Boolean without a null check first.

Solution: Always check if the Boolean variable is null before using it.

Mistake: Assuming that if 'bool' is null, the program will skip the block without an error.

Solution: Understand Java's null handling; performing a direct conditional check on a null reference leads to exceptions.