Java - Getting rid of NullPointerException

Question

Think about two cases case1 and case2 plus two methods method1 and method2. Say method1 solves case1 and method2 solves case2. Now, I have a program that might end up with case1 or case2. In my codes, I call method1 no matter what case happens. But, if case2 occurs, method1 gives a nullpointerexception.

What I want is the following: my codes should call method1 first, if an exception occurs, then method2 is called. How am I gonna do that? Since I have no info about try and catch, I really need some help!

I guess you are right. Say I have TreeNode<City> parentNode which will be the left hand of an equality and the right hand will be search(parent,this) or search2(parent,this). Yet, search and search2 might return null, which I do not want. Now, how should I implement? — johnie walker
– johnie walker, Commented May 26, 2011 at 18:31
please edit your question and post some code sample, not just variable names and method signatures. — khachik
– khachik, Commented May 26, 2011 at 18:33
You could call search1(), then check whether the result is null, and if so, then call search2. If search2 is also null, the equality test should fail. — Andy Thomas
– Andy Thomas, Commented May 26, 2011 at 18:35

Andy Thomas · Accepted Answer · 2011-05-26 18:18:36Z

3

You could do this:

    try {
        method1();
    }
    catch ( Exception e ) {
        method2();
    }

That said, it's typically better to rely on exceptions only for exceptional conditions. For normal flow of control, you can use an if:

    if ( isCase2() ) {
        method2();
    }
    else {
        method1();
    }

answered May 26, 2011 at 18:18

Andy Thomas

86.9k12 gold badges111 silver badges160 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Ted Hopp Over a year ago

As @Vladimir posted, if you're going to go with try/catch, it's better to throw your own exception object from method1 than to rely on a NPE (which might arise even in case 1 due to other problems).

Andy Thomas Over a year ago

Agreed. The first example above is intended to satisfy the OP literally: "my codes should call method1 first, if an exception occurs, then method2 is called." If you can distinguish between case1 and case2 a priori, then that's preferable to using any exception.

Ted Hopp Over a year ago

Absolutely. Use exceptions for exceptional situations. This sounds like having one case versus another is not exceptional at all.

Vladimir Ivanov · Accepted Answer · 2011-05-26 18:17:41Z

Catching NullPointerException is a bad pratice - you may catch not the particular exception you want to catch. You have two options:

1) Throw your own exception and catch it later:

  public void method1(Case caze) throws MyException {
    if (case.getType() == CaseType.CaseOne) {
       // processing
    } else {
       throw new MyException("Wrong case type");
    }
  }

And the client code:

try {
   method1(caze);
} catch (MyException e) {
   // log the excpetion
   method2(caze);
}

2) Return a boolean flag, indicating that the processing has been succesfully finished.

Remember, that it is alway better to analyze the values than use try-catch mechanism in your situations. I would suggest variant #2 for you.

Collectives™ on Stack Overflow

Java - Getting rid of NullPointerException

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related