Catching nullpointerexception in Java

Question

I tried using try-catch block to catch NullPointerException  but still the following program is giving errors  Am I doing something wrong or is there any other way to catch NullPointerException in the following program  Any help is highly appreciated   public class Circular or not                     param args             public static void main String   args                    TODO Auto-generated method stub         try                       LinkedListNode   nodes   new LinkedListNode 10                           for  int i   0  i  lt  10  i                                   nodes i    new LinkedListNode i  null  i  gt  0   nodes i - 1    null                                 Create loop                 nodes 9  next   nodes 3               Boolean abc  Check Circular nodes 0                System out print abc                     catch NullPointerException e                        System out print  NullPointerException caught                          public static boolean Check Circular LinkedListNode head                            LinkedListNode n1   head              LinkedListNode n2   head                   Find meeting point             while  n2 next    null                                 n1   n1 next                   n2   n2 next next                   if  n1    n2                                          return true                                              return false

User · Answer

As stated already within another answer it is not recommended to catch a NullPointerException. However you definitely could catch it, like the following example shows.

public class Testclass{

    public static void main(String[] args) {
        try {
            doSomething();
        } catch (NullPointerException e) {
            System.out.print("Caught the NullPointerException");
        }
    }

    public static void doSomething() {
        String nullString = null;
        nullString.endsWith("test");
    }
}

Although a NPE can be caught you definitely shouldn't do that but fix the initial issue, which is the Check_Circular method.

User · Answer

The problem with your code is in your loop in Check Circular   You are advancing through the list using n1 by going one node at a time   By reassigning n2 to n2 next next you are advancing through it two at a time   When you do that  n2 next next may be null  so n2 will be null after the assignment   When the loop repeats and it checks if n2 next is not null  it throws the NPE because it can t get to next since n2 is already null   You want to do something like what Alex posted instead

User · Answer

You should be catching NullPointerException with the code above  but that doesn t change the fact that your Check Circular is wrong   If you fix Check Circular  your code won t throw NullPointerException in the first place  and work as intended   Try   public static boolean Check Circular LinkedListNode head        LinkedListNode curNode   head      do               curNode   curNode next          if curNode    head              return true            while curNode    null        return false

User · Answer

I think your problem is inside CheckCircular  in the while condition   Assume you have 2 nodes  first N1 and N2 point to the same node  then N1 points to the second node  last  and N2 points to null  because it s N2 next next   In the next loop  you try to call the  next  method on N2  but N2 is null  There you have it  NullPointerException

User · Answer

NullPointerException is a run-time exception which is not recommended to catch it  but instead avoid it   if someVariable    null  someVariable doSomething    else          do something else

[java] Catching nullpointerexception in Java

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