Java从控制台读入数据的几种方法总结

public class TestConsole1 {
  public static void main(String[] args) {
    String str = readDataFromConsole("Please input string：);
    System.out.println("The information from console： + str);
  }

  /**
   * Use InputStreamReader and System.in to read data from console
   * 
   * @param prompt
   *      
   * @return input string
   */
  private static String readDataFromConsole(String prompt) {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String str = null;
    try {
      System.out.print(prompt);
      str = br.readLine();

    } catch (IOException e) {
      e.printStackTrace();
    }
    return str;
  }
}

public class TestConsole2 {
  public static void main(String[] args) {
    String str = readDataFromConsole("Please input string:");
    System.out.println("The information from console:" + str);
  }

  /**
   * Use java.util.Scanner to read data from console
   * 
   * @param prompt
   * 
   * @return input string
   */
  private static String readDataFromConsole(String prompt) {
    Scanner scanner = new Scanner(System.in);
    System.out.print(prompt);
    return scanner.nextLine();
  }
}

public class TestConsole4 {

  public static void main(String[] args) throws IOException {
    FileWriter fw = new FileWriter("num.txt");
    fw.write("2 2.2 3.3 3.33 4.5 done");
    fw.close();

    System.out.println("Sum is "+scanFileForSum("num.txt"));
  }

  public static double scanFileForSum(String fileName) throws IOException {
    double sum = 0.0;
    FileReader fr = null;
    try {
      fr = new FileReader(fileName);
      Scanner scanner = new Scanner(fr);
      
      while (scanner.hasNext()) {
        if (scanner.hasNextDouble()) {
          sum = sum + scanner.nextDouble();

        } else {
          String str = scanner.next();

          if (str.equals("done")) {
            break;
          } else {
            throw new RuntimeException("File Format is wrong!");
          }

        }
      }

    } catch (FileNotFoundException e) {
      throw new RuntimeException("File " + fileName + " not found!");
    } finally {
      if (fr != null)
        fr.close();
    }
    return sum;
  }
}

public class TestConsole3 {
  public static void main(String[] args) {
    String str = readDataFromConsole("Please input string:");
    System.out.println("The information from console:" + str);
  }

  /**
   * Use java.io.console to read data from console
   * 
   * @param prompt
   * 
   * @return input string
   */
  private static String readDataFromConsole(String prompt) {
    Console console = System.console();
    if (console == null) {
      throw new IllegalStateException("Console is not available!");
    }
    return console.readLine(prompt);
  }
}

public class TestConsole5 {
  
   public static void main(String[] args) {
      Console console = System.console();
      if (console == null) {
        throw new IllegalStateException("Console is not available!");
      }
      
      while(true){
      String username = console.readLine("Username: ");
      char[] password = console.readPassword("Password: ");

      if (username.equals("Chris") && String.valueOf(password).equals("GoHead")) {
       console.printf("Welcome to Java Application %1$s.\n", username);
       // 使用后应立即将数组清空，以减少其在内存中占用的时间，增强安全性
        password = null;
       System.exit(-1);
      } 
      else {
       console.printf("Invalid username or password.\n");
      }
      }
     }

}