calling methods in other classes

[elite 98]

hello every one this is my first post here so i thought id say hi. seeing how i'm going to be here more often XD.

i'm working on a small project but cant seem to get past this point. i cant call a function in the other class

public class BankData {
    private static double annual_Interest=3;
    private double monthly_Interest;
    private double balance=100;
    private double charges=2.50;
    private int deposits=0;
    private int withdrawals=0;
    private boolean bool = false;
    
   SavingsAccount acc;

	public void doWithdrawals(int x){
        bool =acc.testWit();                //<~~~~~~~wont work
        if(bool == false){
        balance = balance - x; 
        withdrawals = withdrawals + 1;
        }
    }
class SavingsAccount extends BankData{
    
        public boolean testDep(){  
           return true;
        }
        public boolean testWit(){
            System.out.println("made it here");  //for testing purposes
           return true;
        }
        
    }
}

get called form this over here

 class Listener implements ActionListener { 
         BankData data = new BankData();
        public void actionPerformed(ActionEvent event) { 
            
            if(event.getActionCommand().equals("dep")){

              
            }if(event.getActionCommand().equals("wit")){
            data.doWithdrawals(50);                                //<~~~~called from here
           
                
            }if(event.getActionCommand().equals("info")){
            
            }if(event.getActionCommand().equals("exit")){
                dispose();
                System.exit(0);
            } 
        } 
  }
}

if i'm leaving any important stuff out or its just not clear, sorry about that >.<

[sunde887]

What happens? Errors? If so post the entire error(in code tags), exceptions? Post them too. If nothing, say so.

Also, you don't need to explicitly test booleans in a condition.

boolean b = true;
//to test truth
if(boolean){//do stuff
}
//test  if false
else if(!boolean){}

A guess is that you are getting a null pointer exception. I don't see where you initialize the instance of the inner class SavingAccount. The default constructor will set all objects to null, and numbers to 0.

[elite 98]

What happens? Errors? If so post the entire error(in code tags), exceptions? Post them too. If nothing, say so.

Also, you don't need to explicitly test booleans in a condition.

boolean b = true;
//to test truth
if(boolean){//do stuff
}
//test  if false
else if(!boolean){}

A guess is that you are getting a null pointer exception. I don't see where you initialize the instance of the inner class SavingAccount. The default constructor will set all objects to null, and numbers to 0.

heres the error thanks btw

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at bankaccountv2.BankData.doWithdrawals(BankData.java:19)
	at bankaccountv2.GUI$Listener.actionPerformed(GUI.java:96)
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
	at java.awt.Component.processMouseEvent(Component.java:6288)
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
	at java.awt.Component.processEvent(Component.java:6053)
	at java.awt.Container.processEvent(Container.java:2041)
	at java.awt.Component.dispatchEventImpl(Component.java:4651)
	at java.awt.Container.dispatchEventImpl(Container.java:2099)
	at java.awt.Component.dispatchEvent(Component.java:4481)
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
	at java.awt.Container.dispatchEventImpl(Container.java:2085)
	at java.awt.Window.dispatchEventImpl(Window.java:2478)
	at java.awt.Component.dispatchEvent(Component.java:4481)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:643)
	at java.awt.EventQueue.access$000(EventQueue.java:84)
	at java.awt.EventQueue$1.run(EventQueue.java:602)
	at java.awt.EventQueue$1.run(EventQueue.java:600)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
	at java.awt.EventQueue$2.run(EventQueue.java:616)
	at java.awt.EventQueue$2.run(EventQueue.java:614)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:613)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

[Norm]

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at bankaccountv2.BankData.doWithdrawals(BankData.java :19)

What variable is null at line 19? Find that variable and back track in your code to find out why it has a null value.

[pbrockway2]

You read these things from the top down, paying special attention when you get to a line that mentions your code (because that's where you'll start hunting for the error).

"NullPointerException" means you used a variable which had the value null (ie did not have a value. sorry for the contradiction!) in a context where it should have had a value. A couple of examples might make it clear:

int[] foo = null;
foo[0]; // NPE! foo is null so it doesn't have a zero-th element
String bar = null;
bar.length(); //NPE! bar is null - there is no string - so you can't ask for the length of it

"at bankaccountv2.BankData.doWithdrawals(BankData.java :19)" So look at line 19:

bool =acc.testWit();

It looks like acc is the culprit. So ask yourself: where did you give (or thought you gave) acc a nonnull (real, actual) value? Ie what line of code? Sometimes you do think you gave a variable a good value and then you have to ask: why didn't that happen? Other times you just plain forgot to initialise the variable.

[sunde887]

Like I figured, null pointer exception. Im guessing line 19 is this line

bool =acc.testWit();

Try this snippet, see if it helps you understand

public class X{ 
  public static void main(String[] args){
    String s;
    System.out.println(s);
    s.toString();
  }
}

Or even better, this

public class Y{
  private Z z;
  public String toString(){
    return(z==null)? "null" : z.toString();
  }
  public static void main(String[] args){
    Y y = new Y();
    System.out.println(y); 
  }
  private static class Z{
    int x;
    public String toString(){
      return "X: " + x;
    }
  }
}