Java Tutorial/Development/Console Read

Getting Data From the Keyboard

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
public class MainClass {
  public static void main(String[] av) throws IOException {
    StreamTokenizer tf = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    String s = null;
    int i;
    while ((i = tf.nextToken()) != StreamTokenizer.TT_EOF) {
      switch (i) {
      case StreamTokenizer.TT_EOF:
        System.out.println("End of file");
        break;
      case StreamTokenizer.TT_EOL:
        System.out.println("End of line");
        break;
      case StreamTokenizer.TT_NUMBER:
        System.out.println("Number " + tf.nval);
        break;
      case StreamTokenizer.TT_WORD:
        System.out.println("Word, length " + tf.sval.length() + "->" + tf.sval);
        break;
      default:
        System.out.println("What is it? i = " + i);
      }
    }
  }
}

How to read from standard input

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class MainClass {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    String s;
    while ((s = in.readLine()) != null && s.length() != 0)
      System.out.println(s);
    // An empty line or Ctrl-Z terminates the program
  }
}

Read from keyboard

import java.io.IOException;
public class MainClass {
  public static void main(String[] args) {
    try {
      while (true) {
        int datum = System.in.read();
        if (datum == -1)
          break;
        System.out.println(datum);
      }
    } catch (IOException ex) {
      System.err.println("Couldn"t read from System.in!");
    }
  }
}

Read password from console

/*
 * Copyright (c) 1995 - 2008 Sun Microsystems, Inc.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Sun Microsystems nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
import java.io.Console;
import java.io.IOException;
import java.util.Arrays;
public class Password {
  public static void main(String args[]) throws IOException {
    Console c = System.console();
    if (c == null) {
      System.err.println("No console.");
      System.exit(1);
    }
    String login = c.readLine("Enter your login: ");
    char[] oldPassword = c.readPassword("Enter your old password: ");
    if (verify(login, oldPassword)) {
      boolean noMatch;
      do {
        char[] newPassword1 = c.readPassword("Enter your new password: ");
        char[] newPassword2 = c.readPassword("Enter new password again: ");
        noMatch = !Arrays.equals(newPassword1, newPassword2);
        if (noMatch) {
          c.format("Passwords don"t match. Try again.%n");
        } else {
          change(login, newPassword1);
          c.format("Password for %s changed.%n", login);
        }
        Arrays.fill(newPassword1, " ");
        Arrays.fill(newPassword2, " ");
      } while (noMatch);
    }
    Arrays.fill(oldPassword, " ");
  }
  // Dummy verify method.
  static boolean verify(String login, char[] password) {
    return true;
  }
  // Dummy change method.
  static void change(String login, char[] password) {
  }
}

Tokenizing a Stream from console input

A StreamTokenizer object can recognize the following kinds of tokens:

1. Numbers:
2. Strings:
3. Words:
4. Comments:
5. Whitespace

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
public class MainClass {
  public static void main(String[] av) throws IOException {
    StreamTokenizer tf = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    String s = null;
    int i;
    while ((i = tf.nextToken()) != StreamTokenizer.TT_EOF) {
      switch (i) {
      case StreamTokenizer.TT_EOF:
        System.out.println("End of file");
        break;
      case StreamTokenizer.TT_EOL:
        System.out.println("End of line");
        break;
      case StreamTokenizer.TT_NUMBER:
        System.out.println("Number " + tf.nval);
        break;
      case StreamTokenizer.TT_WORD:
        System.out.println("Word, length " + tf.sval.length() + "->" + tf.sval);
        break;
      default:
        System.out.println("What is it? i = " + i);
      }
    }
  }
}