Question

I have been working on a program and when I run it I get an error that says line 43 and 84 have a NullPointerException. This is the code. I have put comments where line 43 and 84 are. I am trying to make a word processor like Microsoft Word.

import javax.swing.*;
import java.awt.*;

public class Graphics {
    // listing all the components 
    JFrame f1;
    JPanel colorspanel;
    JPanel sizepanel;
    JPanel fontpanel;
    JPanel mainpanel;
    JTextField Maintextfield;
    JLabel colorlabel;
    JLabel sizelabel;
    JLabel fontlabel;
    JButton colorbuttons[];
    JButton sizebuttons[];
    JButton fontbuttons[];

    Graphics() {
        // making instances of panels
        colorspanel = new JPanel();
        sizepanel = new JPanel();
        fontpanel = new JPanel();
        mainpanel = new JPanel();
        // setting the size of the panels
        colorspanel.setSize(216, 144);
        sizepanel.setSize(216, 144);
        fontpanel.setSize(216, 144);
        mainpanel.setSize(612, 756);    
        // making instances of button
        colorbuttons = new JButton[9];
        sizebuttons = new JButton[14];
        fontbuttons = new JButton[9];
        // setting content for buttons
        // colorbuttons
        colorbuttons[0].setBackground(Color.black);//line 43
        colorbuttons[1].setBackground(Color.red);
        colorbuttons[2].setBackground(Color.blue);
        colorbuttons[3].setBackground(Color.yellow);
        colorbuttons[4].setBackground(Color.green);
        colorbuttons[5].setBackground(Color.gray);
        colorbuttons[6].setBackground(Color.DARK_GRAY);
        colorbuttons[7].setBackground(Color.ORANGE);
        colorbuttons[8].setBackground(Color.pink);
        colorbuttons[9].setBackground(Color.magenta);
        // sizebuttons
        sizebuttons[0].setText("8");
        sizebuttons[1].setText("10");
        sizebuttons[2].setText("12");
        sizebuttons[3].setText("14");
        sizebuttons[4].setText("16");
        sizebuttons[5].setText("18");
        sizebuttons[6].setText("20");
        sizebuttons[7].setText("22");
        sizebuttons[8].setText("24");
        sizebuttons[9].setText("26");
        sizebuttons[10].setText("28");
        sizebuttons[11].setText("30");
        sizebuttons[12].setText("32");
        sizebuttons[13].setText("34");
        sizebuttons[14].setText("36");
        // fontbuttons
        fontbuttons[0].setText("New Times Roman");
        fontbuttons[1].setText("Blackadder ITC");
        fontbuttons[2].setText("Andy");
        fontbuttons[3].setText("Buxton Sketch");
        fontbuttons[4].setText("Arial Black");
        fontbuttons[5].setText("Comic Sans MS");
        fontbuttons[6].setText("Old English Text MT");
        fontbuttons[7].setText("SketchFlow Print");
        fontbuttons[8].setText("Harlow Solid Italic");
        fontbuttons[9].setText("Algerian");
        f1.setVisible(true);
    }

    public static void main(String[] args){
        Graphics graphics = new Graphics();//line 84

    }

}

Answer 1

You created an array, but you never populated it with anything. You need to put buttons in the array. A NullPointerException means that you tried to reference something, but a null value was found, not an object with a method or property. For example

Object x = null;
x.toString();  // NPE

vs

Object x = new Object();
x.toString(); // we're in business

In your case, you created an array (over 2 lines; just create everything on one line IMHO), but never put the buttons in it. So when you call colorButtons[0].whatever you are trying to access whatever on the reference at index 0. But since you didn’t put anything in the array, that reference is null.

Do something more like

JButton[] colorButtons = new JButton[9]; // initialize array
for (int i = 0; i < colorButtons.length; i++) {
   JButton button = ... // initialize button each time thru

   // do any common setup on the buttons

   colorButtons[i] = button; // put the button in the array.
}