Error in array (java)

Question

I'm trying to do a calculator program and I have one problem with the object where i store the numbers given.

I'm trying to do a long array of 1 dimenson object, but i don't know why, when I compile, there is one problem in the line of going accumulate these valeur.

If i change de Object doing it not be one array, it works perfectly.

I'm sorry if there is something responded like that, but i searched and I didn't find it. It's too hard too to try to explain this with a title.

The error is:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at calculadora.calc.actionPerformed(calc.java:95) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 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:6505) at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) at java.awt.Component.processEvent(Component.java:6270) at java.awt.Container.processEvent(Container.java:2229) at java.awt.Component.dispatchEventImpl(Component.java:4861) at java.awt.Container.dispatchEventImpl(Container.java:2287) at java.awt.Component.dispatchEvent(Component.java:4687) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422) at java.awt.Container.dispatchEventImpl(Container.java:2273) at java.awt.Window.dispatchEventImpl(Window.java:2719) at java.awt.Component.dispatchEvent(Component.java:4687) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735) at java.awt.EventQueue.access$200(EventQueue.java:103) at java.awt.EventQueue$3.run(EventQueue.java:694) at java.awt.EventQueue$3.run(EventQueue.java:692) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87) at java.awt.EventQueue$4.run(EventQueue.java:708) at java.awt.EventQueue$4.run(EventQueue.java:706) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:705) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138) at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

And my code is:

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusListener;
import javax.swing.*;


public class calc extends JFrame implements ActionListener {
    JButton nou = new JButton("9");
    JButton vuit = new JButton("8");
    JButton set = new JButton("7");
    JButton sis = new JButton("6");
    JButton cinc = new JButton("5");
    JButton quatre = new JButton("4");
    JButton tres = new JButton("3");
    JButton dos = new JButton("2");
    JButton un = new JButton("1");
    JButton zero = new JButton("0");
    JButton mes = new JButton("+");
    JButton menys = new JButton("-");
    JButton mem = new JButton("Ans");
    JButton borrar = new JButton("Borrar");
    JButton igual = new JButton("=");
    JTextField texte= new JTextField("0",10);
   long v[];
   long v2;
   int i=0;
   long u=0;
   String muestra;

   int memo;
    public calc (){
       super("Calculadora Carlos. Congrats!");
       setSize(400,400);
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       JPanel num = new JPanel();
       JPanel op = new JPanel();
       JPanel tex = new JPanel();
       un.addActionListener(this);
       dos.addActionListener(this);
       tres.addActionListener(this);
       quatre.addActionListener(this);
       cinc.addActionListener(this);
       sis.addActionListener(this);
       set.addActionListener(this);
       vuit.addActionListener(this);
       nou.addActionListener(this);
       mes.addActionListener(this);
       menys.addActionListener(this);
       mem.addActionListener(this);
       borrar.addActionListener(this);
       igual.addActionListener(this);
       texte.setEditable(false);
       GridLayout numeros = new GridLayout(4,3,5,5);
       num.setLayout(numeros);
       num.add(nou);
       num.add(vuit);
       num.add(set);
       num.add(sis);
       num.add(cinc);
       num.add(quatre);
       num.add(tres);
       num.add(dos);
       num.add(un);
       num.add(zero);

     GridLayout operacions = new GridLayout(5,1,5,5);
        op.setLayout(operacions);
        op.add(mes);
        op.add(menys);
        op.add(mem);
        op.add(borrar);
        op.add(igual);

        GridLayout text = new GridLayout(3,4,5,5);
        tex.setLayout(text);
        tex.add(texte);



getContentPane().add(num, BorderLayout.CENTER); 
 getContentPane().add(tex, BorderLayout.NORTH);     
 getContentPane().add(op, BorderLayout.EAST);  

        setVisible(true);
    }
  public void actionPerformed(ActionEvent evt) {

      Object A=evt.getSource();
      while(i==0){
      if(A==un){
          u=v[i];
          v[i]=u*10+1;
          muestra=muestra+"1";
          texte.setText(muestra);
      }}
 }



    public static void main(String[] args) {
   calc carlos=new calc();
    }
}

Sorry If my english is not the best of the world. I'm not an english speaker.

Ross Drew · Accepted Answer · 2013-12-05 10:25:15Z

2

v[] is never initialized, so it will NullPointerException when you try to access it here

u=v[i];

answered Dec 5, 2013 at 10:25

Ross Drew

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6 Comments

user3069682 Over a year ago

But how I initalize if i don't want to decide the lenght of the array? is not possible?

Ross Drew Over a year ago

No, arrays length needs to be set on initialization. If you want a variable length list you need to use one of the Collections like ArrayList

Christian Kullmann Over a year ago

If you do not want to decide on the length of an array, you should go with an ArrayList<Long> instead of long[] for example.

Prasad Over a year ago

@user3069682 what are you going to store in v[] ? ArrayList is the best option for this. To play with this you dont need to specify the length.

Paul Samsotha Over a year ago

I may be wrong, but does while(i == 0) have a funny smell to it?

|

Rohan · Accepted Answer · 2013-12-05 10:28:39Z

1

In your code you have only declared array long v[] but not initialized it.So this line u=v[i]; is might be throwing exception. You need to initialzed it as long v[]=new long[size];

Also if you don't want to define array size during initialization then you can use ArrayList also.

answered Dec 5, 2013 at 10:28

Rohan

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3 Comments

user3069682 Over a year ago

Thank you for all the responses! this webpage is amazing! I did the next changes long v[]= new long[3]; //line 28 v[i]=v[i]*10+1; //line 96 When i compile it works, but when i press one button, it freezes? any idea?

Ross Drew Over a year ago

check @peeskillet comment on the end of my post, that may be why

Rohan Over a year ago

@user3069682 I guess while(i==0) this might be causing infinite loop.you are not incrementing value of i.

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