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0 Answer(s)      7 years ago
Posted in : Java Beginners
I want to do show histogram, when the user clicks the button, a new window appears that displays a histogram to show the occurrence of the letters in the text area.
This is my coding,

import javax.swing.*;
import java.awt.*;
public class Histogram extends JPanel {
// Count the occurrence of 26 letters
private int[] count;

/** Set the count and display histogram */
public void showHistogram(int[] count) {
this.count = count;

/** Paint the histogram */
protected void paintComponent(Graphics g) {
if (count == null) return; // No display if count is null
// Find the panel size and bar width and interval dynamically
int width = getWidth();
int height = getHeight();
int interval = (width - 40) / count.length;
int individualWidth = (int)(((width - 40) / 24) * 0.60);
// Find the maximum count. The maximum count has the highest bar
int maxCount = 0;
for (int i = 0; i < count.length; i++) {
if (maxCount < count[i])
maxCount = count[i];

g.drawLine(10, height - 45, 10, 10);

// x is the start position for the first bar in the histogram
int x = 30;
// Draw a horizontal base line
g.drawLine(10, height - 45, width - 10, height - 45);
for (int i = 0; i < count.length; i++) {
// Find the bar height
int barHeight =
(int)(((double)count[i] / (double)maxCount) * (height - 55));
// Display a bar (i.e. rectangle)
g.drawRect(x, height - 45 - barHeight, individualWidth,
// Display a letter under the base line
g.drawString((char)(65 + i) + "", x, height - 30);
// Move x for displaying the next character
x += interval;

/** Override getPreferredSize */
public Dimension getPreferredSize() {
return new Dimension(300, 300);

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MultipleWindowsDemo extends JFrame {
private JTextArea jta;
private JButton jbtShowHistogram = new JButton("Show Histogram");
private Histogram histogram = new Histogram();
// Create a new frame to hold the histogram panel
private JFrame histogramFrame = new JFrame();

public MultipleWindowsDemo() {
// Store text area in a scroll pane
JScrollPane scrollPane = new JScrollPane(jta = new JTextArea());
scrollPane.setPreferredSize(new Dimension(300, 200));
// Place scroll pane and button in the frame
add(scrollPane, BorderLayout.CENTER);
add(jbtShowHistogram, BorderLayout.SOUTH);
// Register listener
jbtShowHistogram.addActionListener(new ActionListener() {
/** Handle the button action */
public void actionPerformed(ActionEvent e) {
// Count the letters in the text area
int[] count = countLetters();
// Set the letter count to histogram for display
histogramFrame.setVisible(true); // Show the frame

// Create a new frame to hold the histogram panel

/** Count the letters in the text area */
private int[] countLetters() {
// Count for 26 letters
int[] count = new int[26];
// Get contents from the text area
String text = jta.getText();
// Count occurrence of each letter (case insensitive)
for (int i = 0; i < text.length(); i++) {
char character = text.charAt(i);
if ((character >= 'A') && (character <= 'Z')) {
count[(int)character - 65]++; // The ASCII for 'A' is 65
else if ((character >= 'a') && (character <= 'z')) {
count[(int)character - 97]++; // The ASCII for 'a' is 97
return count; // Return the count array

public static void main(String[] args) {
MultipleWindowsDemo frame = new MultipleWindowsDemo();
frame.setLocationRelativeTo(null); // Center the frame

In the histogram class, i create 'g.drawLine(10, height - 45, 10, 10);'.
When I run it, it shows y-axis..but how to make y-axis has number?I mean for example when user type 'MMM' at text area, then the bar for M is 3.

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