I have written this code and it gives NullPointerException

Question

import java.awt.*;
import java.awt.event.*;

public class sample2 extends Frame
    {
    Button b[];
    public sample2()
        {
        super("trying");
        b=new Button[10];
        setLayout(new FlowLayout());
        for(int i=0;i<10;i++)
            add(b[i]);
        }
    public static void main(String args[])
        {
        sample2 obj=new sample2();
        obj.setSize(500,100);
        obj.setVisible(true);
        }
    }

Exception is as below

Exception in thread "main" java.lang.NullPointerException 
at java.awt.Container.addImpl(Container.java:1037) 
at java.awt.Container.add(Container.java:373) 
at sample2.<init>(sample2.java:13) 
at sample2.main(sample2.java:17) 

Answer 1

Yes you create the Button array, but you never initialize the elements of the array before using. This means that you're adding null Buttons to your GUI. Create your Buttons first before using.

    for(int i=0;i<10;i++)
        b[i] = new Button();
        add(b[i]);
    }