如何使用按钮从另一个类调用方法？

Question

I'm pretty new to Java, I'm trying to make a basic UI. I can use JButtons to call JOptionPanes easily, but what I can't do is use them to call anything from another class.

Currently I have my main class, my UI class, and my class that handles my data.

In my class that handles my data I have a method that performs a basic sum on 2 elements of an array:

    public void firstMonth(){
        String ans;
        int num1 = Integer.parseInt(sortedData[0][0][0]);
        int num2 = Integer.parseInt(sortedData[0][0][1]);
        int sum = num1 * num2;

        ans=String.format("The sum of day1 and day2 is: %s", sum);
        JOptionPane.showMessageDialog(null, ans, "Title", JOptionPane.PLAIN_MESSAGE);

    }

Then in my UI class I try and call it when one of the buttons is pressed:

public class UserInterface extends JFrame {

GetData a = new GetData();

    private class myhandler implements ActionListener{

        public void actionPerformed(ActionEvent event){

            if(event.getSource()==button1){
                a.firstMonth();

            }
}
}

But when I press the button I get more exceptions that I can bear to count. Any ideas?

Sorry if this is a really basic question.

Edit, here are the exceptions I get when I click the button:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: null
    at java.lang.Integer.parseInt(Integer.java:454)
    at java.lang.Integer.parseInt(Integer.java:527)
    at pkg110_term3.GetData.firstMonth(GetData.java:75)
    at pkg110_term3.UserInterface$myhandler.actionPerformed(UserInterface.java:71)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$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:729)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:688)
    at java.awt.EventQueue$3.run(EventQueue.java:686)
    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:702)
    at java.awt.EventQueue$4.run(EventQueue.java:700)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
    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)

Answer 1

In your main class, this line - ans=String.format("The sum of day1 and day2 is: %s", sum);

Why do you use %s , that means a String variable and sum is an int . Use %d instead.

Also what are the values stored in sortedData[0][0][0] and sortedData[0][0][1] ?

Answer 2

Given that Integer.parseInt takes a String argument, it's safe to say that sortedData is a 3D String array. From your stacktrace, the array sortedData is initialized but the individual elements are not .

The default value for Object types is null . The same applys for values within an Object array.

Make sure these elements have been assigned values prior to invoking Integer.parseInt .

for (int i=0; i < sortedData.length; i++) {
   for (int j=0; j < sortedData[i].length; j++) {
      for (int k=0; k < sortedData[i][j].length; k++) {
         sortedData[i][j][k] = ... // some string
      }
   }
}