Greenfoot

Pointifix

2014/3/20

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Hi. My Problem is that i want to add an object to an empty list, but when i do so it throws nullpointnerexception, whats my mistake?:

1 2	`if(storeballs.isEmpty())storeballs.set(0,(BilliardBall)billiardball.get(i));` `else` `storeballs.add((BilliardBall)billiardball.get(i));`

bourne

2014/3/20

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You shouldn't need the if and else. You should be fine with just:

1	`storeballs.add((BilliardBall)billiardball.get(i));`

My guess is that billiardball or storeballs is not initiated.

Pointifix

2014/3/20

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how to initiate correctly? List storeballs = ?

bourne

2014/3/20

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Since List is an interface, you can't initialize as List, you can initialize it as something that implements List, such as ArrayList.

1	`ArrayList<Ball> storeballs =` `new` `ArrayList<Ball>();`

where Ball is your type. Might want to check this link out to learn about generics: http://docs.oracle.com/javase/tutorial/java/generics/why.html

Pointifix

2014/3/20

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jeah thanks alot ;)

List Empty?