What is NullPointerException?

NullPointerException is a RuntimeException . In Java, a special null value can be assigned to an object reference. NullPointerException is thrown when an application attempts to use an object reference that has the null value. These include: Calling an instance method on the object referred by a null reference.

Please click here to know in details : NullPointerException

Sample code for generating NullPointerException

package com.javaskool;

public class TestDrive {

  public static void main(String[] args) {
    String intPartLength = null;
    try {
        
        System.out.println(intPartLength.substring(5, 10));
        
        } catch (NullPointerException npe) {
            System.out.println("NullPointerException Error. Message: " + npe.getMessage());
            npe.printStackTrace();
        } catch (NumberFormatException nfe) {
            System.out.println("NumberFormatException Error. Message: " + nfe.getMessage());
            nfe.printStackTrace();
        } catch (Exception e) {
            System.out.println("General Error. Message: " + e.getMessage());
            e.printStackTrace();
    }
  }

}

And the Error Message will be

NullPointerException Error. Message: null
java.lang.NullPointerException
	at com.javaskool.TestDrive.main(TestDrive.java:9)