What is NullPointerException in Java?

java.lang.NullPointerException occurs during runtime when a method of an object, belonging to a class is invoked, given the object value is null. In this java tutorial, we shall see how a NullPointerException occurs and the ways to handle java.lang.NullPointerException.

Example 1 – Recreate NullPointerException

In this example, we will recreate NullPointerException by calling a method/routine on an object which is having **null** value.

Example.java

package com.tut;

/**
 * @author arjun
 */
public class Example {

	public static void main(String[] args) {
		String words = null;
		String[] wordArray = words.split("\t");
		for(String word:wordArray){
			System.out.println(word);
		}
	}

}

When the program is run, we get a NullPointerException at line words.split(“\t”), where the value of words is null. The output is shown below:

Exception in thread "main" java.lang.NullPointerException
	at com.tut.NullPointerExceptionExample.main(NullPointerExceptionExample.java:10)

How to handle java.lang.NullPointerException ?

Top handle this NullPointerException, do a null check for the object before accessing the methods/routines/behaviors of it.

Example 2 – Handle NullPointerException using Null Check

In the following example, before calling split() method on words array, we are checking if words object is not null using if statement.

Example.java

package com.tut;

/**
 * @author arjun
 */
public class Example {

	public static void main(String[] args) {
		String words = null;

		String[] wordArray = null;
		if(words!=null){
			wordArray = words.split("\t");
		}
		if(wordArray!=null){
			for(String word:wordArray){
				System.out.println(word);
			}
		}
		System.out.println("Program handles NullPointerException.");
	}
}

Even though, the code above is a dead code, it still demonstrates to first check if an object is null, and then proceed with accessing its methods. When the code is run, the output is as shown in the following.

Output

Program handles NullPointerException.

Example 3 – Handle NullPointerException using Try-Catch

Or, you can use Try-Catch block around the code snippet that has the potential to throw NullPointerException.

Example.java

package com.tut;

/**
 * @author arjun
 */
public class Example {

	public static void main(String[] args) {
		String words = null;
		String[] wordArray = null;

		try {
			wordArray = words.split("\t");
			try {
				for(String word:wordArray){
					System.out.println(word);
				}
			} catch (NullPointerException e) {
				System.out.println("wordArray is holding null. NullPointerException is handled.");
			}
		} catch (NullPointerException e) {
			System.out.println("words is holding null. NullPointerException is handled.");
		}
	}
}

Here, we used a try-catch block inside a try-catch block, for catching NullPointerException that could be thrown by the possible objects, which are String objects in this example. Well, the object could be of any class type. When the above program is run, the output is as shown in the following.

Output

words is holding null. NullPointerException is handled.

Conclusion

In this Java Tutorial, we learned what NullPointerException is and how we handle java.lang.NullPointerException.