Java Object(Boolean,Integer) when add get NullPointerException

Question

When I try to reset a list Marked I get a Null Pointer Exception.

The problem must be cause I never said what B and C is. (Boolean B, Integer C) And I don't know how to do this.

Here is a part of my code :

Marked[] marked;


//Create list marked!
public class Marked<B,C>{
    public B bool;
    public C comp;
}

public Graph(int N)
{

    //Fill marked with false and 0
    marked = new Marked[N];
    for(int i=0;i<N;i++){

        marked[i].bool = false;
        marked[i].comp=0;
    }

Alexis C. · Accepted Answer · 2013-11-18 17:43:07Z

5

Creating an array of Marked doesn't actually initialize the elements in the array:

marked = new Marked[N];
for(int i = 0; i < N; i++) {
    marked[i] = new Marked<Boolean, Integer>();
    marked[i].bool = false;
    marked[i].comp = 0;
}

edited Nov 18, 2013 at 17:43

Alexis C.

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answered Nov 18, 2013 at 17:32

Justin Niessner

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1 Comment

Alexis C. Over a year ago

@STUDENT_LIFE Don't forget to accept the answer if it has helped you =)

Mureinik · Accepted Answer · 2013-11-18 17:33:30Z

2

The statement marked = new Marked[N]; creates a new array of Marked objects with N elements, but does not initialize them. Each element in this array would be null. You need to manually initialize them by calling the constructor.

So, your for loop should look like this:

for(int i=0;i<N;i++) {
    marked[i] = new Marked();
    marked[i].bool = false;
    marked[i].comp=0;
}

answered Nov 18, 2013 at 17:33

Mureinik

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1 Comment

STUDENT_LIFE Over a year ago

Thank you both for your fast reply! :)

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