What will be the output of this code? Please explain how the Autoboxing or unboxing id done here.

class MyBoolean
{
    Boolean[] bool = new Boolean[5];

    public static void main(String[] args)
    {
      new MyBoolean().myMethod();
    }

    public void myMethod()
    {
      if(bool[1]==true)
      {
        System.out.println("It's true");
      }
      else
      {
        System.out.println("It's false");
      }
    }
}

• java
• boolean

The code fails with a NullPointerException because bool[1] contains null. According to the Java Language Specification, Section 5.1.8, the unboxing of a Boolean is done by calling booleanValue() on the Boolean reference. Since in this case, the reference is null, you get an NPE.

In a comment on another answer, you wrote:

The reason to ask this question is to understand if we get the NPE via AutoUnBoxing or via AutoBoxing. In my understanding its due to AutoBoxing.

It's due to unboxing (extracting a primitive from a reference type), not boxing (wrapping a primative in a reference type). Specifically, from JLS Section 15.21.2 (Boolean Equality Operators == and !=):

If one of the operands is of type Boolean, it is subjected to unboxing conversion (§5.1.8).

Run fails: bool[1] is null and comparison throw NullPointerException.