NullPointerException, Trying to add JPanel Array to Container

Question

Can't figure out why I am getting this exception, Console returns this message:

public static void main(String [] args){
JFrame b = new JFrame("Lotus");
Container pieces = new Container();
JLabel[] labelsP1 = new JLabel[10];
JLabel[] labelsP2 = new JLabel[10];

for(int i = 0 ; i < labelsP1.length ; i++){
    labelsP1[i] = new JLabel(B1); 
    for(int j = 0 ; j < labelsP2.length ; j++){
        labelsP2[j] = new JLabel(B2); 
    }
    for (JLabel label : labelsP1) {
        pieces.add(label);
    }

    Container c = b.getContentPane();
    c.setLayout(new GridLayout(13,3)); 
    c.add(pieces);
}

I've reformatted your code - it would be really helpful if you could format your code nicely when posting questions in future. Please read tinyurl.com/so-hints. Also, you haven't told us anything about pieces. — Jon Skeet
– Jon Skeet, Commented Apr 5, 2013 at 18:35

Anthony Raimondo · Accepted Answer · 2013-04-05 18:44:34Z

3

your 3rd inner loop is iterating throw a null array

 for (JLabel label : labelsP1) {
        pieces.add(label);
    }

//

for(int i = 0 ; i < labelsP1.length ; i++)
{
    labelsP1[i] = new JLabel(B1); 
    for(int j = 0 ; j < labelsP2.length ; j++)
    {
        labelsP2[j] = new JLabel(B2); 
    }
    for (JLabel label : labelsP1)   // null only labelsP1[0] is initialized
    {
        pieces.add(label);        
    }

    Container c = b.getContentPane();
    c.setLayout(new GridLayout(13,3)); 
    c.add(pieces);
}

edited Apr 5, 2013 at 18:44

answered Apr 5, 2013 at 18:37

Anthony Raimondo

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2 Comments

Joop Eggen Over a year ago

As labelsP1 is filled upto i. Also the nesting of for i and for j suggests one new JLabel[] should happen inside the first for i.

Anthony Raimondo Over a year ago

check Deadron comment, it looks like your code is missing a bracket.

Deadron · Accepted Answer · 2013-04-05 18:36:01Z

2

For starters it does not look like you are showing us all the code which things difficult. Secondly, is it the intent that your first for loop is containing all of the code after it? It seems likely you have a bracket misplacement issue. I would guess you need a closing brace.

for(int i = 0 ; i < labelsP1.length ; i++){
        labelsP1[i] = new JLabel(B1); 
        for(int j = 0 ; j < labelsP2.length ; j++){
            labelsP2[j] = new JLabel(B2); 
    }

to

for(int i = 0 ; i < labelsP1.length ; i++) {
    labelsP1[i] = new JLabel(B1);
}

for(int j = 0 ; j < labelsP2.length ; j++) {
    labelsP2[j] = new JLabel(B2); 
}

answered Apr 5, 2013 at 18:36

Deadron

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Comments

Ankur Shanbhag · Accepted Answer · 2013-04-05 18:39:44Z

0

In thie code below :

for(int i = 0 ; i < labelsP1.length ; i++){
labelsP1[i] = new JLabel(B1); 
for(int j = 0 ; j < labelsP2.length ; j++){
    labelsP2[j] = new JLabel(B2); 
}
for (JLabel label : labelsP1) {
    pieces.add(label);
}

You are adding JLabels to the array labelsP1 one by one and also iterating over the array. But you are trying to access all the elements from it which does not exist.

I would suggest you to remove nested for loops to get proper behaviour and avoid NullPointerException.

answered Apr 5, 2013 at 18:39

Ankur Shanbhag

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