Chapter 22 Exercise 18, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

22.18 (Binary search animation) Write a program that animates the binary search algorithm. Create an array with numbers from 1 to 20 in this order. The array elements are displayed in a histogram, as shown in Figure 22.13. You need to enter a search key in the text field. Clicking the Step button causes the program to perform one comparison in the algorithm. Use a light-gray color to paint the bars for the numbers in the current search range and use a black color to paint the a bar indicating the middle number in the search range. The Step button also freezes the text field to prevent its value from being changed. When the algorithm is finished, display the status in a label at the top of a border pane. Clicking the Reset button enables a new search to start. This button also makes the text field editable.

import javax.swing.*;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;

public class Exercise18 extends JApplet {

 private static final long serialVersionUID = 1L;
 private BinarySearchPanel binarySearchPanel = new BinarySearchPanel();
 private JTextField jTextField = new JTextField("37", 5);
 
 public Exercise18() {
  setLayout(new BorderLayout());
  add(binarySearchPanel, BorderLayout.CENTER);
  
  JPanel panel1 = new JPanel();
  panel1.add(new JLabel("Key (in double): "));
  panel1.add(jTextField);
  JButton jButton1 = new JButton("Step");
  panel1.add(jButton1);
  JButton jButton2 = new JButton("Reset");
  panel1.add(jButton2);
  add(panel1, BorderLayout.SOUTH); 
  
  jButton1.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    try {
     int value = Integer.parseInt(jTextField.getText());
     jTextField.setEditable(false);
     if (binarySearchPanel.isValid(value)) {
      if (binarySearchPanel.step(value)) {
       JOptionPane.showMessageDialog(null, "Key found!", "Finish", JOptionPane.INFORMATION_MESSAGE);
       binarySearchPanel.reset();
       jTextField.setEditable(true);
      }; 
     } else {
      JOptionPane.showMessageDialog(null, "Key not found!", "Error", JOptionPane.ERROR_MESSAGE);
      binarySearchPanel.reset();
      jTextField.setEditable(true);      
     }
    } catch (NumberFormatException e2) {
    }
   }
  });
  
  jButton2.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    jTextField.setEditable(true);
    binarySearchPanel.reset();
   }
  });
 }

 static class BinarySearchPanel extends JPanel {
  private static final long serialVersionUID = 1L;
  private int searchSize = 50;
  private int startPosition = -1;
  private int endPosition = searchSize;
  private int stepPosition = -1;
  ArrayList<Integer> numbers = new ArrayList<>();
  
  public boolean isValid(int value) {
   if ((value < numbers.get(0)) || (value > numbers.get(numbers.size() - 1))) {
    return false;
   } else {
    return true;
   }
  }
  
  public BinarySearchPanel() {
   for (int i = 1; i <= searchSize; i++) {
    numbers.add(i);
   }
   reset();
  }
  
  public boolean step(int value) {
   if(stepPosition == -1) {
    startPosition++;
    endPosition--;
   } else if(value > numbers.get(stepPosition)) {
    startPosition = stepPosition + 1;
   } else if(value < numbers.get(stepPosition)) {
    endPosition = stepPosition - 1;
   }  
   stepPosition = (endPosition + startPosition) / 2;
   repaint();
   return numbers.get(stepPosition) == value;   
  }
  
  public void reset() {
   startPosition = -1;
   endPosition = searchSize;
   stepPosition = -1;
   repaint();
  }
  
  @Override
  protected void paintComponent(Graphics g) {
   super.paintComponent(g);
   int numberWidth = getWidth() / (searchSize + 2);
   int numberHeight = getHeight() / (searchSize + 2);
   if(stepPosition != -1) {
    g.setColor(Color.LIGHT_GRAY);
    for (int i = startPosition; i <= endPosition; i++) {
     g.fillRect(numberWidth * (i + 1), getHeight() - numberHeight * numbers.get(i), numberWidth, numberHeight * numbers.get(i));
    }
    g.setColor(Color.BLACK); 
    g.fillRect(numberWidth * (stepPosition + 1), getHeight() - numberHeight * numbers.get(stepPosition), numberWidth, numberHeight * numbers.get(stepPosition));
   }
   for (int i = 0; i < searchSize; i++) {
    g.drawRect(numberWidth * (i + 1), getHeight() - numberHeight * numbers.get(i), numberWidth, numberHeight * numbers.get(i));
    g.drawString(numbers.get(i) + "", numberWidth * (i + 1), getHeight() - numberHeight * numbers.get(i) - (int)(numberHeight * 0.5));
   }

  }

 }

 public static void main(String[] args) {
  JFrame frame = new JFrame("Exercise18");
  Exercise18 applet = new Exercise18();
  frame.add(applet);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setSize(960, 500);
  frame.setMinimumSize(new Dimension(frame.getWidth(), frame.getHeight()));
  frame.setLocationRelativeTo(null);
  frame.setVisible(true);
 }
}