Help With adding a scrollbar to my applet

Question

This is the source code of my applet.I wat to have an autoscroll on this applet
i think it is usefull if i put here all the code for my project.
======================================================
Class ConsolePanel:
The file defines a class ConsolePanel. Objects of type
ConsolePanel can be used for simple input/output exchanges with
the user. Various routines are provided for reading and writing
values of various types from the output. (This class gives all
the I/O behavior of another class, Console, that represents a
separate window for doing console-style I/O.)
This class is dependent on another class, ConsoleCanvas.
Note that when the console has the input focus, it is outlined with
a bright blue border. If, in addition, the console is waiting for
user input, then there will be a blinking cursor. If the console
is not outlined in light blue, the user has to click on it before
any input will be accepted.
This is an update an earlier version of the same class,
rewritten to use realToString() for output of floating point
numbers..
package myproj;
import java.awt.*;
import java.awt.event.*;
import javax.swing.JScrollPane;
import javax.swing.JScrollBar;
import javax.swing.*;
public class ConsolePanel extends JTextArea{
static public JScrollPane scrollPane;
// ***************************** Constructors *******************************
public ConsolePanel() { // default constructor just provides default window title and size
setBackground(Color.white);
setLayout(new BorderLayout(0, 0));
canvas = new ConsoleCanvas(500,1000);
scrollPane = new JScrollPane(canvas);
scrollPane.setVerticalScrollBarPolicy(
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
scrollPane.setPreferredSize( new Dimension( 1000,10000) );
add("Center", scrollPane);
//scrollPane.getVerticalScrollBar().setUnitIncrement(1);
try {
jbInit();
} catch (Exception ex) {
ex.printStackTrace();
public void clear() { // clear all characters from the canvas
canvas.clear();
// *************************** I/O Methods *********************************
// Methods for writing the primitive types, plus type String,
// to the console window, with no extra spaces.
// Note that the real-number data types, float
// and double, a rounded version is output that will
// use at most 10 or 11 characters. If you want to
// output a real number with full accuracy, use
// "con.put(String.valueOf(x))", for example.
public void put(int x) {
put(x, 0);
} // Note: also handles byte and short!
public void put(long x) {
put(x, 0);
public void put(double x) {
put(x, 0);
} // Also handles float.
public void put(char x) {
put(x, 0);
public void put(boolean x) {
put(x, 0);
public void put(String x) {
put(x, 0);
// Methods for writing the primitive types, plus type String,
// to the console window,followed by a carriage return, with
// no extra spaces.
public void putln(int x) {
put(x, 0);
newLine();
} // Note: also handles byte and short!
public void putln(long x) {
put(x, 0);
newLine();
public void putln(double x) {
put(x, 0);
newLine();
} // Also handles float.
public void putln(char x) {
put(x, 0);
newLine();
public void putln(boolean x) {
put(x, 0);
newLine();
public void putln(String x) {
put(x, 0);
newLine();
// Methods for writing the primitive types, plus type String,
// to the console window, with a minimum field width of w,
// and followed by a carriage return.
// If outut value is less than w characters, it is padded
// with extra spaces in front of the value.
public void putln(int x, int w) {
put(x, w);
newLine();
} // Note: also handles byte and short!
public void putln(long x, int w) {
put(x, w);
newLine();
public void putln(double x, int w) {
put(x, w);
newLine();
} // Also handles float.
public void putln(char x, int w) {
put(x, w);
newLine();
public void putln(boolean x, int w) {
put(x, w);
newLine();
public void putln(String x, int w) {
put(x, w);
newLine();
// Method for outputting a carriage return
public void putln() {
newLine();
// Methods for writing the primitive types, plus type String,
// to the console window, with minimum field width w.
public void put(int x, int w) {
dumpString(String.valueOf(x), w);
} // Note: also handles byte and short!
public void put(long x, int w) {
dumpString(String.valueOf(x), w);
public void put(double x, int w) {
dumpString(realToString(x), w);
} // Also handles float.
public void put(char x, int w) {
dumpString(String.valueOf(x), w);
public void put(boolean x, int w) {
dumpString(String.valueOf(x), w);
public void put(String x, int w) {
dumpString(x, w);
// Methods for reading in the primitive types, plus "words" and "lines".
// The "getln..." methods discard any extra input, up to and including
// the next carriage return.
// A "word" read by getlnWord() is any sequence of non-blank characters.
// A "line" read by getlnString() or getln() is everything up to next CR;
// the carriage return is not part of the returned value, but it is
// read and discarded.
// Note that all input methods except getAnyChar(), peek(), the ones for lines
// skip past any blanks and carriage returns to find a non-blank value.
// getln() can return an empty string; getChar() and getlnChar() can
// return a space or a linefeed ('\n') character.
// peek() allows you to look at the next character in input, without
// removing it from the input stream. (Note that using this
// routine might force the user to enter a line, in order to
// check what the next character.)
// Acceptable boolean values are the "words": true, false, t, f, yes,
// no, y, n, 0, or 1; uppercase letters are OK.
// None of these can produce an error; if an error is found in input,
// the user is forced to re-enter.
// Available input routines are:
// getByte() getlnByte() getShort() getlnShort()
// getInt() getlnInt() getLong() getlnLong()
// getFloat() getlnFloat() getDouble() getlnDouble()
// getChar() getlnChar() peek() getAnyChar()
// getWord() getlnWord() getln() getString() getlnString()
// (getlnString is the same as getln and is onlyprovided for consistency.)
public byte getlnByte() {
byte x = getByte();
emptyBuffer();
return x;
public short getlnShort() {
short x = getShort();
emptyBuffer();
return x;
public int getlnInt() {
int x = getInt();
emptyBuffer();
return x;
public long getlnLong() {
long x = getLong();
emptyBuffer();
return x;
public float getlnFloat() {
float x = getFloat();
emptyBuffer();
return x;
public double getlnDouble() {
double x = getDouble();
emptyBuffer();
return x;
public char getlnChar() {
char x = getChar();
emptyBuffer();
return x;
public boolean getlnBoolean() {
boolean x = getBoolean();
emptyBuffer();
return x;
public String getlnWord() {
String x = getWord();
emptyBuffer();
return x;
public String getlnString() {
return getln();
} // same as getln()
public String getln() {
StringBuffer s = new StringBuffer(100);
char ch = readChar();
while (ch != '\n') {
s.append(ch);
ch = readChar();
return s.toString();
public byte getByte() {
return (byte) readInteger( -128L, 127L);
public short getShort() {
return (short) readInteger( -32768L, 32767L);
public int getInt() {
return (int) readInteger((long) Integer.MIN_VALUE,
(long) Integer.MAX_VALUE);
public long getLong() {
return readInteger(Long.MIN_VALUE, Long.MAX_VALUE);
public char getAnyChar() {
return readChar();
public char peek() {
return lookChar();
public char getChar() { // skip spaces & cr's, then return next char
char ch = lookChar();
while (ch == ' ' || ch == '\n') {
readChar();
if (ch == '\n') {
dumpString("? ", 0);
ch = lookChar();
return readChar();
public float getFloat() { // can return positive or negative infinity
float x = 0.0F;
while (true) {
String str = readRealString();
if (str.equals("")) {
errorMessage("Illegal floating point input.",
"Real number in the range " + Float.MIN_VALUE +
" to " + Float.MAX_VALUE);
} else {
Float f = null;
try {
f = Float.valueOf(str);
} catch (NumberFormatException e) {
errorMessage("Illegal floating point input.",
"Real number in the range " + Float.MIN_VALUE +
" to " + Float.MAX_VALUE);
continue;
if (f.isInfinite()) {
errorMessage("Floating point input outside of legal range.",
"Real number in the range " + Float.MIN_VALUE +
" to " + Float.MAX_VALUE);
continue;
x = f.floatValue();
break;
return x;
public double getDouble() {
double x = 0.0;
while (true) {
String str = readRealString();
if (str.equals("")) {
errorMessage("Illegal floating point input",
"Real number in the range " + Double.MIN_VALUE +
" to " + Double.MAX_VALUE);
} else {
Double f = null;
try {
f = Double.valueOf(str);
} catch (NumberFormatException e) {
errorMessage("Illegal floating point input",
"Real number in the range " + Double.MIN_VALUE +
" to " + Double.MAX_VALUE);
continue;
if (f.isInfinite()) {
errorMessage("Floating point input outside of legal range.",
"Real number in the range " + Double.MIN_VALUE +
" to " + Double.MAX_VALUE);
continue;
x = f.doubleValue();
break;
return x;
public String getWord() {
char ch = lookChar();
while (ch == ' ' || ch == '\n') {
readChar();
if (ch == '\n') {
dumpString("? ", 0);
ch = lookChar();
StringBuffer str = new StringBuffer(50);
while (ch != ' ' && ch != '\n') {
str.append(readChar());
ch = lookChar();
return str.toString();
public boolean getBoolean() {
boolean ans = false;
while (true) {
String s = getWord();
if (s.equalsIgnoreCase("true") || s.equalsIgnoreCase("t") ||
s.equalsIgnoreCase("yes") || s.equalsIgnoreCase("y") ||
s.equals("1")) {
ans = true;
break;
} else if (s.equalsIgnoreCase("false") || s.equalsIgnoreCase("f") ||
s.equalsIgnoreCase("no") || s.equalsIgnoreCase("n") ||
s.equals("0")) {
ans = false;
break;
} else {
errorMessage("Illegal boolean input value.",
"one of: true, false, t, f, yes, no, y, n, 0, or 1");
return ans;
// ***************** Everything beyond this point is private *******************
// ********************** Utility routines for input/output ********************
private ConsoleCanvas canvas; // the canvas where I/O is displayed
private String buffer = null; // one line read from input
private int pos = 0; // position next char in input line that has
// not yet been processed
private String readRealString() { // read chars from input following syntax of real numbers
StringBuffer s = new StringBuffer(50);
char ch = lookChar();
while (ch == ' ' || ch == '\n') {
readChar();
if (ch == '\n') {
dumpString("? ", 0);
ch = lookChar();
if (ch == '-' || ch == '+') {
s.append(readChar());
ch = lookChar();
while (ch == ' ') {
readChar();
ch = lookChar();
} while (ch >= '0' && ch <= '9') {
s.append(readChar());
ch = lookChar();
if (ch == '.') {
s.append(readChar());
ch = lookChar();
while (ch >= '0' && ch <= '9') {
s.append(readChar());
ch = lookChar();
if (ch == 'E' || ch == 'e') {
s.append(readChar());
ch = lookChar();
if (ch == '-' || ch == '+') {
s.append(readChar());
ch = lookChar();
} while (ch >= '0' && ch <= '9') {
s.append(readChar());
ch = lookChar();
return s.toString();
private long readInteger(long min, long max) { // read long integer, limited to specified range
long x = 0;
while (true) {
StringBuffer s = new StringBuffer(34);
char ch = lookChar();
while (ch == ' ' || ch == '\n') {
readChar();
if (ch == '\n') {
dumpString("? ", 0);
ch = lookChar();
if (ch == '-' || ch == '+') {
s.append(readChar());
ch = lookChar();
while (ch == ' ') {
readChar();
ch = lookChar();
} while (ch >= '0' && ch <= '9') {
s.append(readChar());
ch = lookChar();
if (s.equals("")) {
errorMessage("Illegal integer input.",
"Integer in the range " + min + " to " + max);
} else {
String str = s.toString();
try {
x = Long.parseLong(str);
} catch (NumberFormatException e) {
errorMessage("Illegal integer input.",
"Integer in the range " + min + " to " + max);
continue;
if (x < min || x > max) {
errorMessage("Integer input outside of legal range.",
"Integer in the range " + min + " to " + max);
continue;
break;
return x;
private static String realToString(double x) {
// Goal is to get a reasonable representation of x in at most
// 10 characters, or 11 characters if x is negative.
if (Double.isNaN(x)) {
return "undefined";
if (Double.isInfinite(x)) {
if (x < 0) {
return "-INF";
} else {
return "INF";
if (Math.abs(x) <= 5000000000.0 && Math.rint(x) == x) {
return String.valueOf((long) x);
String s = String.valueOf(x);
if (s.length() <= 10) {
return s;
boolean neg = false;
if (x < 0) {
neg = true;
x = -x;
s = String.valueOf(x);
if (x >= 0.00005 && x <= 50000000 &&
(s.indexOf('E') == -1 && s.indexOf('e') == -1)) { // trim x to 10 chars max
s = round(s, 10);
s = trimZeros(s);
} else if (x > 1) { // construct exponential form with positive exponent
long power = (long) Math.floor(Math.log(x) / Math.log(10));
String exp = "E" + power;
int numlength = 10 - exp.length();
x = x / Math.pow(10, power);
s = String.valueOf(x);
s = round(s, numlength);
s = trimZeros(s);
s += exp;
} else { // constuct exponential form
long power = (long) Math.ceil( -Math.log(x) / Math.log(10));
String exp = "E-" + power;
int numlength = 10 - exp.length();
x = x * Math.pow(10, power);
s = String.valueOf(x);
s = round(s, numlength);
s = trimZeros(s);
s += exp;
if (neg) {
return "-" + s;
} else {
return s;
private static String trimZeros(String num) { // used by realToString
if (num.indexOf('.') >= 0 && num.charAt(num.length() - 1) == '0') {
int i = num.length() - 1;
while (num.charAt(i) == '0') {
i--;
if (num.charAt(i) == '.') {
num = num.substring(0, i);
} else {
num = num.substring(0, i + 1);
return num;
private static String round(String num, int length) { // used by realToString
if (num.indexOf('.') < 0) {
return num;
if (num.length() <= length) {
return num;
if (num.charAt(length) >= '5' && num.charAt(length) != '.') {
char[] temp = new char[length + 1];
int ct = length;
boolean rounding = true;
for (int i = length - 1; i >= 0; i--) {
temp[ct] = num.charAt(i);
if (rounding && temp[ct] != '.') {
if (temp[ct] < '9') {
temp[ct]++;
rounding = false;
} else {
temp[ct] = '0';
ct--;
if (rounding) {
temp[ct] = '1';
ct--;
// ct is -1 or 0
return new String(temp, ct + 1, length - ct);
} else {
return num.substring(0, length);
private void dumpString(String str, int w) { // output string to console
for (int i = str.length(); i < w; i++) {
canvas.addChar(' ');
for (int i = 0; i < str.length(); i++) {
if ((int) str.charAt(i) >= 0x20 && (int) str.charAt(i) != 0x7F) { // no control chars or delete
canvas.addChar(str.charAt(i));
} else if (str.charAt(i) == '\n' || str.charAt(i) == '\r') {
newLine();
private void errorMessage(String message, String expecting) {
// inform user of error and force user to re-enter.
newLine();
dumpString(" *** Error in input: " + message + "\n", 0);
dumpString(" *** Expecting: " + expecting + "\n", 0);
dumpString(" *** Discarding Input: ", 0);
if (lookChar() == '\n') {
dumpString("(end-of-line)\n\n", 0);
} else {
while (lookChar() != '\n') {
canvas.addChar(readChar());
dumpString("\n\n", 0);
dumpString("Please re-enter: ", 0);
readChar(); // discard the end-of-line character
private char lookChar() { // return next character from input
if (buffer == null || pos > buffer.length()) {
fillBuffer();
if (pos == buffer.length()) {
return '\n';
return buffer.charAt(pos);
private char readChar() { // return and discard next character from input
char ch = lookChar();
pos++;
return ch;
private void newLine() { // output a CR to console
canvas.addCR();
private void fillBuffer() { // Wait for user to type a line and press return,
// and put the typed line into the buffer.
buffer = canvas.readLine();
pos = 0;
private void emptyBuffer() { // discard the rest of the current line of input
buffer = null;
public void clearBuffers() { // I expect this will only be called by
// CanvasApplet when a program ends. It should
// not be called in the middle of a running program.
buffer = null;
canvas.clearTypeAhead();
private void jbInit() throws Exception {
this.setNextFocusableComponent(scrollPane);
this.setToolTipText("");
} // end of class Console
============================================================
Class ConsoleCanvas:
/* A class that implements basic console-oriented input/output, for use with
Console.java and ConsolePanel.java. This class provides the basic character IO.
Higher-leve fucntions (reading and writing numbers, booleans, etc) are provided
in Console.java and ConolePanel.java.
(This vesion of ConsoleCanvas is an udate of an earilier version, rewritten to
be compliand with Java 1.1. David Eck; July 17, 1998.)
(Modified August 16, 1998 to add the
a mousePressed method to ConsoleCanvas. The mousePressed method requests
the focus. This is necessary for Sun's Java implementation -- though not,
apparently for anyone else's. Also added: an isFocusTraversable() method)
MouseListener interface and
Minor modifications, February 9, 2000, some glitches in the graphics.
package myproj;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class ConsoleCanvas extends JTextArea implements FocusListener, KeyListener,
MouseListener {
// public interface, constructor and methods
public ConsoleCanvas(int u,int y) {
addFocusListener(this);
addKeyListener(this);
try {
jbInit();
} catch (Exception ex) {
ex.printStackTrace();
public final String readLine() { // wait for user to enter a line of input;
// Line can only contain characters in the range
// ' ' to '~'.
return doReadLine();
public final void addChar(char ch) { // output PRINTABLE character to console
putChar(ch);
public final void addCR() { // add a CR to the console
putCR();
public synchronized void clear() { // clear console and return cursor to row 0, column 0.
if (OSC == null) {
return;
currentRow = 0;
currentCol = 0;
OSCGraphics.setColor(Color.white);
OSCGraphics.fillRect(4, 4, getSize().width - 8, getSize().height - 8);
OSCGraphics.setColor(Color.black);
repaint();
try {
Thread.sleep(25);
} catch (InterruptedException e) {}
// focus and key event handlers; not meant to be called excpet by system
public void keyPressed(KeyEvent evt) {
doKey(evt.getKeyChar());
public void keyReleased(KeyEvent evt) {}
public void keyTyped(KeyEvent evt) {}
public void focusGained(FocusEvent evt) {
doFocus(true);
public void focusLost(FocusEvent evt) {
doFocus(false);
public boolean isFocusTraversable() {
// Allows the user to move the focus to the canvas
// by pressing the tab key.
return true;
// Mouse listener methods -- here just to make sure that the canvas
// gets the focuse when the user clicks on it. These are meant to
// be called only by the system.
public void mousePressed(MouseEvent evt) {
requestFocus();
public void mouseReleased(MouseEvent evt) {}
public void mouseClicked(MouseEvent evt) {}
public void mouseEntered(MouseEvent evt) {}
public void mouseExited(MouseEvent evt) {}
// implementation section: protected variables and methods.
protected StringBuffer typeAhead = new StringBuffer();
// Characters typed by user but not yet processed;
// User can "type ahead" the charcters typed until
// they are needed to satisfy a readLine.
protected final int maxLineLength = 256;
// No lines longer than this are returned by readLine();
// The system effectively inserts a CR after 256 chars
// of input without a carriage return.
protected int rows, columns; // rows and columns of chars in the console
protected int currentRow, currentCol; // current curson position
protected Font font; // Font used in console (Courier); All font
// data is set up in the doSetup() method.
protected int lineHeight; // height of one line of text in the console
protected int baseOffset; // distance from top of a line to its baseline
protected int charWidth; // width of a character (constant, since a monospaced font is used)
protected int leading; // space between lines
protected int topOffset; // distance from top of console to top of text
protected int leftOffset; // distance from left of console to first char on line
protected Image OSC; // off-screen backup for console display (except cursor)
protected Graphics OSCGraphics; // graphics context for OSC
protected boolean hasFocus = false; // true if this canvas has the input focus
protected boolean cursorIsVisible = false; // true if cursor is currently visible
private int pos = 0; // exists only for sharing by next two methods
public synchronized void clearTypeAhead() {
// clears any unprocessed user typing. This is meant only to
// be called by ConsolePanel, when a program being run by
// console Applet ends. But just to play it safe, pos is
// set to -1 as a signal to doReadLine that it should return.
typeAhead.setLength(0);
pos = -1;
notify();
protected synchronized String doReadLine() { // reads a line of input, up to next CR
if (OSC == null) { // If this routine is called before the console has
// completely opened, we shouldn't procede; give the
// window a chance to open, so that paint() can call doSetup().
try {
wait(5000);
} catch (InterruptedException e) {} // notify() should be set by doSetup()
if (OSC == null) { // If nothing has happened for 5 seconds, we are probably in
// trouble, but when the heck, try calling doSetup and proceding anyway.
doSetup();
if (!hasFocus) { // Make sure canvas has input focus
requestFocus();
StringBuffer lineBuffer = new StringBuffer(); // buffer for constructing line from user
pos = 0;
while (true) { // Read and process chars from the typeAhead buffer until a CR is found.
while (pos >= typeAhead.length()) { // If the typeAhead buffer is empty, wait for user to type something
cursorBlink();
try {
wait(500);
} catch (InterruptedException e) {}
if (pos == -1) { // means clearTypeAhead was called;
return ""; // this is an abnormal return that should not happen
if (cursorIsVisible) {
cursorBlink();
if (typeAhead.charAt(pos) == '\r' || typeAhead.charAt(pos) == '\n') {
putCR();
pos++;
break;
if (typeAhead.charAt(pos) == 8 || typeAhead.charAt(pos) == 127) {
if (lineBuffer.length() > 0) {
lineBuffer.setLength(lineBuffer.length() - 1);
eraseChar();
pos++;
} else if (typeAhead.charAt(pos) >= ' ' &&
typeAhead.charAt(pos) < 127) {
putChar(typeAhead.charAt(pos));
lineBuffer.append(typeAhead.charAt(pos));
pos++;
} else {
pos++;
if (lineBuffer.length() == maxLineLength) {
putCR();
pos = typeAhead.length();
break;
if (pos >= typeAhead.leng

Answer 1

Hi
I don't understand the exact need you want
you want to add Scrolling facility to your Entire Applet or only for the Textarea Class?
In first case
Create the ScrollPane and add it to the applet contentPane. and put entire components to a Panel and just add it to scroll pane.
Regards
Vinoth