Reading a text file line by line in Java ME

From Nokia Developer Wiki
Jump to: navigation, search

This code snippet demonstrates how to read a text file line by line (note that unlike Java SE with its BufferedReader class, Java ME doesn't provide the functionality).



import java.io.IOException;
import java.io.InputStreamReader;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.midlet.MIDlet;
public class ReaderMIDlet extends MIDlet implements CommandListener {
private Form mainForm;
private Command exitCommand;
* Constructor. Constructs the object and initializes displayables.

public ReaderMIDlet() {
mainForm = new Form("Example MIDlet");
exitCommand = new Command("Exit", Command.EXIT, 1);
try {
} catch (IOException ex) {
// TODO: Exception handling
* Outputs the specified file onto the form.
* @throws java.io.IOException if an exception occurs when reading the
* file

private void readFile(String filename) throws IOException {
InputStreamReader reader = new InputStreamReader(
String line = null;
// Read a single line from the file. null represents the EOF.
while ((line = readLine(reader)) != null) {
// Append the read line to the main form with a linefeed ('\n')
mainForm.append(line + "\n");
* Reads a single line using the specified reader.
* @throws java.io.IOException if an exception occurs when reading the
* line

private String readLine(InputStreamReader reader) throws IOException {
// Test whether the end of file has been reached. If so, return null.
int readChar = reader.read();
if (readChar == -1) {
return null;
StringBuffer string = new StringBuffer("");
// Read until end of file or new line
while (readChar != -1 && readChar != '\n') {
// Append the read character to the string. Some operating systems
// such as Microsoft Windows prepend newline character ('\n') with
// carriage return ('\r'). This is part of the newline character
// and therefore an exception that should not be appended to the
// string.
if (readChar != '\r') {
// Read the next character
readChar = reader.read();
return string.toString();
* From MIDlet.
* Called when the MIDlet is started.

public void startApp() {
// The initial display is the first form
* From MIDlet.
* Called to signal the MIDlet to enter the Paused state.

public void pauseApp() {
// No implementation required
* From MIDlet.
* Called to signal the MIDlet to terminate.
* @param unconditional whether the MIDlet has to be unconditionally
* terminated

public void destroyApp(boolean unconditional) {
// No implementation required
* From CommandListener.
* Called by the system to indicate that a command has been invoked on a
* particular displayable.
* @param command the command that was invoked
* @param displayable the displayable where the command was invoked

public void commandAction(Command command, Displayable displayable) {
if (command == exitCommand) {
// Exit the MIDlet

Supplementary material


The specified text file is output onto the form.

Version Hint

Windows Phone: [[Category:Windows Phone]]
[[Category:Windows Phone 7.5]]
[[Category:Windows Phone 8]]

Nokia Asha: [[Category:Nokia Asha]]
[[Category:Nokia Asha Platform 1.0]]

Series 40: [[Category:Series 40]]
[[Category:Series 40 1st Edition]] [[Category:Series 40 2nd Edition]]
[[Category:Series 40 3rd Edition (initial release)]] [[Category:Series 40 3rd Edition FP1]] [[Category:Series 40 3rd Edition FP2]]
[[Category:Series 40 5th Edition (initial release)]] [[Category:Series 40 5th Edition FP1]]
[[Category:Series 40 6th Edition (initial release)]] [[Category:Series 40 6th Edition FP1]] [[Category:Series 40 Developer Platform 1.0]] [[Category:Series 40 Developer Platform 1.1]] [[Category:Series 40 Developer Platform 2.0]]

Symbian: [[Category:Symbian]]
[[Category:S60 1st Edition]] [[Category:S60 2nd Edition (initial release)]] [[Category:S60 2nd Edition FP1]] [[Category:S60 2nd Edition FP2]] [[Category:S60 2nd Edition FP3]]
[[Category:S60 3rd Edition (initial release)]] [[Category:S60 3rd Edition FP1]] [[Category:S60 3rd Edition FP2]]
[[Category:S60 5th Edition]]
[[Category:Symbian^3]] [[Category:Symbian Anna]] [[Category:Nokia Belle]]

This page was last modified on 30 July 2013, at 08:26.
229 page views in the last 30 days.