NullPointerException is a kind of unchecked exception that occurs when an application attempts to use null in a case where an object is required. It is also known as runtime time exception, which occurs while running a program. This type of exception is internal to the application and extends the java.lang.RuntimeException that is inherited from java.lang.Exception class.

NullPointerException must bethrown when an application attempts to use null in a case where an object is required. These include:

• Calling the instance method of a null object.
• Accessing or modifying the field of a null object.
• Taking the length of null as if it were an array.
  

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