/*
 * 
 * File: SimpleButtons.java
 * 
 * Description: The GUI of this program contains four number 
 * buttons and a textfield. It consists of a panel that uses a 
 * Border layout manager containing a text field and another 
 * panel that uses a Group layout manager. The smaller panel 
 * contains the four buttons.  When a button is pressed, the 
 * label that belongs to the button appears at the bottom of 
 * the GUI in the textfield.
 * 
 */
/**
 * 
 * @author: put-your-name-here
 *
 */

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Main extends JPanel implements ActionListener {
  
  private static final long serialVersoinUID = 1L;
  private final static int numButtons = 4; // number of buttons, used in a loop
  private JButton[] buttonKeys; // array to hold button numbers
  private JTextField numberField; // to hold button labels ('0','1','2','3')
  /**
   * Constructor:
   * Creates the GUI and implements Border and Group layout managers
   */
  public Main() {
    // set layout manager for GUI (Border layout)
    setLayout(new BorderLayout());
        
    numberField = new JTextField(50);    //text field
        
    // create panel to hold buttons
    JPanel numberPanel = new JPanel();
    numberPanel.setMaximumSize(new Dimension(400,40));    //set size of panel
        
    // set layout manager for panel that holds the buttons (Group layout)
    GroupLayout layout = new GroupLayout(numberPanel);
    numberPanel.setLayout(layout);    
        
    buttonKeys = new JButton[numButtons];//array of buttons
        
    // set labels, add action listener, set size for each button, 
    // and prevent border from appearing around selected button
    for (int i = 0; i < numButtons; i++) {
      buttonKeys[i] = new JButton(Integer.toString(i));
      buttonKeys[i].addActionListener(this);
      buttonKeys[i].setMaximumSize(new Dimension(200,60));
      buttonKeys[i].setFocusPainted(false);
    }
        
    // Horizontally align components
    layout.setHorizontalGroup(
      layout.createSequentialGroup()
      .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addComponent(buttonKeys[0])
        .addComponent(buttonKeys[2])
      )
      .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addComponent(buttonKeys[1])
        .addComponent(buttonKeys[3])        
      )
    );
                        
    // Vertically align components
    layout.setVerticalGroup(
      layout.createSequentialGroup()
      .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addComponent(buttonKeys[0])
        .addComponent(buttonKeys[1])
      )
      .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
        .addComponent(buttonKeys[2])
        .addComponent(buttonKeys[3])
      )
    );
    
    // add panel holding the buttons and the text field
    add(numberPanel, BorderLayout.CENTER);
    add(numberField, BorderLayout.SOUTH);
  }  //constructor
    
  /**
   * Event handler:
   *   When a button is pressed, the label that belongs to the 
   *   button appears at the bottom of the GUI in the text field.
   *   
   * @param a String representing the event (button clicked)
   */
  public void actionPerformed(ActionEvent e) {
    JButton b = (JButton) e.getSource();
    numberField.setText( b.getText() );
  } // event handler
    
  // launch the GUI
  public static void main( String args[ ] ) { 
    SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        Main myNumbers = new Main(); // create SimpleButtons object
        JFrame myFrame = new JFrame();    // create JFrame
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        myFrame.getContentPane().add(myNumbers);
        myFrame.setSize(400,400);        //set size of program
        myFrame.setResizable(true);    //prevent resizing program
        myFrame.setVisible(true);        //make GUI visible
      }
    });        
  } // end main here
}