null pointer exception after checking for null pointers

Question

I am getting a null pointer exception despite checking with an if statement first whether the value is null. Here is my code:

Collections.sort(taskList,new Comparator<Task>(){ //here is one NPE
        @Override
        public int compare(Item t1,Item t2){
            if((t1.getAssignedString()!=null)&&(t2.getAssignedString()!=null)){ //here is second NPE
            int x=t1.getAssignedString().compareTo(t2.getAssignedString());

            if(x!=0){return x;}
            else{
                Integer x1=(int)(4*(((Task)t1).getAllottedTime()));
                Integer x2=(int)(4*(((Task)t2).getAllottedTime()));
                return x1.compareTo(x2);
            }
            }
            else{System.out.println("null value");
            return 0;}
        }

    });

Why is this check not working? Is there a way round this?

You are checking t1.getAssignedString(), but not t1.

Oliver Charlesworth
– Oliver Charlesworth

2014-05-03 11:30:09 +00:00
Commented May 3, 2014 at 11:30 — Oliver Charlesworth
– Oliver Charlesworth, Commented May 3, 2014 at 11:30

Rakesh KR · Accepted Answer · 2014-05-03 11:31:45Z

1

You are checking t1.getAssignedString() is null , you need to check t1!=null.

For the case of t2 also.

answered May 3, 2014 at 11:31

Rakesh KR

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Gabriel Ruiu · Accepted Answer · 2014-05-03 11:31:22Z

0

Im guessing that you need to check if the actual instances are not null, like taskList and the individual Item instances when comparing (t1 and t2).

answered May 3, 2014 at 11:31

Gabriel Ruiu

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Comments

Arif Khan · Accepted Answer · 2014-05-03 12:16:43Z

0

Before using t1 and t2, you should test whether t1 or t2 must not be null

Collections.sort(taskList,new Comparator<Task>(){ //here is one NPE
            @Override
            public int compare(Item t1,Item t2){
                if(t1==null || t2==null){
                  return 0;
                }
                ...

answered May 3, 2014 at 12:16

Arif Khan

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