Avoiding NullPointerException in Java

0 votes

I use object != null a lot to avoid NullPointerException.

What is an alternative to:

if (someobject != null) {

Dec 21, 2020 in Java by Rajiv
• 8,880 points

1 answer to this question.

0 votes

This to me sounds like a reasonably common problem that junior to intermediate developers tend to face at some point: they either don't know or don't trust the contracts they are participating in and defensively overcheck for nulls. Additionally, when writing their own code, they tend to rely on returning nulls to indicate something thus requiring the caller to check for nulls.

To put this another way, there are two instances where null checking comes up:

  1. Where null is a valid response in terms of the contract; and

  2. Where it isn't a valid response.

(2) is easy. Either use assert statements (assertions) or allow failure (for example, NullPointerException). Assertions are a highly-underused Java feature that was added in 1.4. The syntax is:

assert <condition>


assert <condition> : <object>

where <condition> is a boolean expression and <object> is an object whose toString() method's output will be included in the error.

An assert statement throws an Error (AssertionError) if the condition is not true. By default, Java ignores assertions. You can enable assertions by passing the option -ea to the JVM. You can enable and disable assertions for individual classes and packages. This means that you can validate code with the assertions while developing and testing, and disable them in a production environment, although my testing has shown next to no performance impact from assertions.

Not using assertions in this case is OK because the code will just fail, which is what will happen if you use assertions. The only difference is that with assertions it might happen sooner, in a more-meaningful way and possibly with extra information, which may help you to figure out why it happened if you weren't expecting it.

(1) is a little harder. If you have no control over the code you're calling then you're stuck. If null is a valid response, you have to check for it.

If it's code that you do control, however (and this is often the case), then it's a different story. Avoid using nulls as a response. With methods that return collections, it's easy: return empty collections (or arrays) instead of nulls pretty much all the time.

With non-collections it might be harder. Consider this as an example: if you have these interfaces:

public interface Action {
  void doSomething();

public interface Parser {
  Action findAction(String userInput);

where Parser takes raw user input and finds something to do, perhaps if you're implementing a command line interface for something. Now you might make the contract that it returns null if there's no appropriate action. That leads the null checking you're talking about.

An alternative solution is to never return null and instead use the Null Object pattern:

public class MyParser implements Parser {
  private static Action DO_NOTHING = new Action() {
    public void doSomething() { /* do nothing */ }

  public Action findAction(String userInput) {
    // ...
    if ( /* we can't find any actions */ ) {
      return DO_NOTHING;


Parser parser = ParserFactory.getParser();
if (parser == null) {
  // now what?
  // this would be an example of where null isn't (or shouldn't be) a valid response
Action action = parser.findAction(someInput);
if (action == null) {
  // do nothing
} else {



which is a much better design because it leads to more concise code.

That said, perhaps it is entirely appropriate for the findAction() method to throw an Exception with a meaningful error message -- especially in this case where you are relying on user input. It would be much better for the findAction method to throw an Exception than for the calling method to blow up with a simple NullPointerException with no explanation.

try {
} catch(ActionNotFoundException anfe) {

Or if you think the try/catch mechanism is too ugly, rather than Do Nothing your default action should provide feedback to the user.

public Action findAction(final String userInput) {
    /* Code to return requested Action if found */
    return new Action() {
        public void doSomething() {
            userConsole.err("Action not found: " + userInput);
answered Dec 21, 2020 by Gitika
• 65,870 points

Related Questions In Java

+1 vote
3 answers

What is the syntax to declare and initialize an array in java?

You can use this method: String[] strs = ...READ MORE

answered Jul 25, 2018 in Java by samarth295
• 2,200 points
0 votes
2 answers

How can I convert a String variable to a primitive int in Java

 Here are two ways illustrating this: Integer x ...READ MORE

answered Aug 20, 2019 in Java by Sirajul
• 58,990 points
0 votes
5 answers

How to compare Strings in Java?

String fooString1 = new String("foo"); String fooString2 = ...READ MORE

answered Jul 12, 2018 in Java by Daisy
• 8,110 points
+1 vote
2 answers

How to generate random integers within specific range in Java?

You can achieve that concisely in Java: Random ...READ MORE

answered Jul 25, 2018 in Java by samarth295
• 2,200 points
0 votes
2 answers

What is null in java?

"null" is a reference type and its ...READ MORE

answered Jul 31, 2018 in Java by Mrunal
• 680 points
+5 votes
4 answers

How to execute a python file with few arguments in java?

You can use Java Runtime.exec() to run python script, ...READ MORE

answered Mar 27, 2018 in Java by DragonLord999
• 8,450 points

edited Nov 6, 2018 by Omkar 38,594 views
+1 vote
1 answer

How to handle drop downs using Selenium WebDriver in Java

First, find an XPath which will return ...READ MORE

answered Mar 27, 2018 in Selenium by nsv999
• 5,520 points
0 votes
1 answer

What are the differences between getText() and getAttribute() functions in Selenium WebDriver?

See, both are used to retrieve something ...READ MORE

answered Apr 5, 2018 in Selenium by nsv999
• 5,520 points
0 votes
6 answers

How can we define global variables in java?

To define Global Variable you can make ...READ MORE

answered Dec 15, 2020 in Java by Gitika
• 65,870 points
+15 votes
25 answers

How can I convert String to JSON object in Java?

Hi @Daisy You can use Google gson  for more ...READ MORE

answered Feb 7, 2019 in Java by Suresh
• 720 points