Linear Search Woes

[Marie Jeanne Thibault]

Hi!
Can anyone give me a hint as to why my linear search won't work? When a number is entered in the index textfield and click the show button, that element should be displayed in the element textfield. I get all sorts of exception messages. Anything would be appreciated.
Here's the code:
//ArrayDemo.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ArrayDemo extends JFrame implements ActionListener {
    //Declare two textfields
    private JTextField jtfIndex = new JTextField(8);
    private JTextField jtfElement = new JTextField(8);
    private JButton jbtShow = new JButton("Show Element");
    //Declare "Show Element" button
    int list[];
    //Constructor
    public ArrayDemo() {
        setTitle("Show Bounds Error");
        //Create panel for the textfields
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(2, 2));
        p1.add(new JLabel("Array Index"));
        p1.add(jtfIndex);
        p1.add(new JLabel("Array Element"));
        p1.add(jtfElement);
        //Create panel for button
        JPanel p2 = new JPanel();
        p2.setLayout(new FlowLayout());
        p2.add(jbtShow);
        //Set panels in frame
        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(p1, BorderLayout.CENTER);
        getContentPane().add(p2, BorderLayout.SOUTH);
        //Register Listener
        jtfIndex.addActionListener(this);
        jbtShow.addActionListener(this);
    }
    //Main Method
    public static void main(String[] args) {
        int key;
        int list[];
        list = new int[100];
        for (int i = 0; i < list.length; i++) {
            list[i] = (int) (Math.random() * 1000);
        }
        ArrayDemo frame = new ArrayDemo();
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setSize(200, 100);
    }
    public static int linearSearch(int list[], int key) {
        for (int i = 0; i < list.length; i++)
            if (list[i] == key)
                return i;
        return -1;
    }
    //The nitty gritty
    public void actionPerformed(ActionEvent e) {
        int key = (Integer.parseInt(jtfIndex.getText()));
        int result = linearSearch(list, key);
        if (e.getSource() == jbtShow)
            if (result != -1)
                jtfElement.setText(String.valueOf(result));
            else
                jtfElement.setText("Out of Bounds");
    }
}

Thanks,
Marie
[ January 31, 2004: Message edited by: Jim Yingst ]

[Ernest Friedman-Hill]

I didn't examine the program extremely closely, but one major problem is that there are two variables named "list": one is a member of ArrayDemo; this one is never initialized. Another is local to main(), and this one is the one that gets initialized. All the methods of ArrayDemo try to use the uninitialized one.
To fix this, you could move the code that creates the array and populates it from main() into the ArrayDemo constructor, being careful to remove the line "int[] list" that declares the local variable, so that it's the member that gets initialized instead.