Question

Na is a parameter. I’m sure that this parameter is correct.
I’ve declared an array of Na JTextField, And I would like to use one of them. But when I run my code, There is an exception…

That’s my code :

import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

class Panneau_fenetre1A extends JPanel                      
{   
    public Panneau_fenetre1A(int Na)
    {
        JTextField[] allField = new JTextField [Na];
        for(int i = 0;i<Na;i++)
        {
            allField[i].setText(String.valueOf(0));
            allField[i].setBounds(150, 350+i*25,20, 20);
        }
    }

}

That’s the exception :

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Panneau_fenetre1A.<init>(Panneau_fenetre1A.java:18)
    at Cadre_fenetre1A.<init>(Cadre_fenetre1A.java:13)
    at Panneau_fenetre$ecout1.actionPerformed(Panneau_fenetre.java:64)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2012)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2335)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:404)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6268)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
    at java.awt.Component.processEvent(Component.java:6033)
    at java.awt.Container.processEvent(Container.java:2045)
    at java.awt.Component.dispatchEventImpl(Component.java:4629)
    at java.awt.Container.dispatchEventImpl(Container.java:2103)
    at java.awt.Component.dispatchEvent(Component.java:4455)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4633)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4297)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4227)
    at java.awt.Container.dispatchEventImpl(Container.java:2089)
    at java.awt.Window.dispatchEventImpl(Window.java:2517)
    at java.awt.Component.dispatchEvent(Component.java:4455)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:649)
    at java.awt.EventQueue.access$000(EventQueue.java:96)
    at java.awt.EventQueue$1.run(EventQueue.java:608)
    at java.awt.EventQueue$1.run(EventQueue.java:606)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:116)
    at java.awt.EventQueue$2.run(EventQueue.java:622)
    at java.awt.EventQueue$2.run(EventQueue.java:620)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:619)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)

Answer 1

This line…

JTextField[] allField = new JTextField [Na];

initializes a new ARRAY, which will hold JTextField objects. The array has -Na- spaces in it, but each space is still empty. You still need to create the JTextField object to go into the empty array spaces.

Something like this should work…

for(int i = 0;i < Na;i++)
{
    allField[i] = new JTextField(String.valueOf(0));
    allField[i].setBounds(150, 350 + i * 25, 20, 20);

}