Greenfoot

Mepp

2013/2/25

#

When I compile the code, all is ok, but when i try to run it, it says everytime "java.lang.NullpointerException". Why?

it marked "if(mi.getActor()==start){"

danpost

2013/2/25

#

The 'getMouseInfo' method will return 'null' unless there is a mouse action to record. Before trying to 'getActor' from the MouseInfo object, first check to see if the MouseInfo object is 'null'.

Mepp

2013/2/25

#

I written it this way now:

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if(gamestatus==1){
    MouseInfo mi=Greenfoot.getMouseInfo();
    if(mi.getActor()!=null){
        if(mi.getActor()==start) setImage("Clear.png");
    }
}

But it says the same at line 3 now. The same here also:

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if(gamestatus==1){
    MouseInfo mi=Greenfoot.getMouseInfo();
    if(mi.getActor()!=null && mi.getActor()==start) setImage("Clear.png");
}

davmac

2013/2/25

#

You're still calling a method on what getMouseInfo returned:

1	`if(mi.getActor()!=null){`

Here 'mi' might be null, but you're calling getActor() on it. You need to check if mi is null before calling any methods on it:

1	`if(mi !=` `null){`

There's no need to check if mi.getActor() returns null, because you don't call any methods on that.

Mepp

2013/2/25

#

Thx, working now! :)

Mepp

2013/2/25

#

Got another NullpointerException now:

The spf.addObject... was marked Just the NullpointerException, the other Errors are cleared.

davmac

2013/2/25

#

That means that 'spf' is null. It is the same problem - you are calling a method on a null reference.

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java.lang.nullpointerException-Error