Java從控制臺讀入數據的幾種方法 – JAVA編程語言程序開發技術文章

這裡記錄Java中從控制臺讀入信息的幾種方式,已備後查!

(1)JDK 1.4(JDK 1.5和JDK 1.6也都兼容這種方法)

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 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 www.aiwalls.com
     */
    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;
    }
}
 
(2)JDK 1.5(利用Scanner進行讀取)

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 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();
    }
}
 
Scanner還可以很方便的掃描文件,讀取裡面的信息並轉換成你要的類型,比如對“2 2.2 3.3 3.33 4.5 done”這樣的數據求和,見如下代碼:
 
 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 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;
    }
}
(3)JDK 1.6(利用java.io.Console進行讀取)

JDK6中提供瞭java.io.Console類專用來訪問基於字符的控制臺設備.
你的程序如果要與Windows下的cmd或者Linux下的Terminal交互,就可以用Console類代勞.(類似System.in和System.out)
但我們不總是能得到可用的Console, 一個JVM是否有可用的Console依賴於底層平臺和JVM如何被調用.
如果JVM是在交互式命令行(比如Windows的cmd)中啟動的,並且輸入輸出沒有重定向到另外的地方,那麼就可以得到一個可用的Console實例。

在使用 IDE 的情況下,是無法獲取到Console實例的,原因在於在 IDE 的環境下,重新定向瞭標準輸入和輸出流,也是就是將系統控制臺上的輸入輸出重定向到瞭 IDE 的控制臺中

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 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);
    }
}
 
Console類還有個特色就是,專門對密碼(輸入無回顯)等安全字符,進行瞭處理。專門提供 readPassword()方法,具體應用見如下代碼:
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);               // 使用後應立即將數組清空,以減少其在內存中占用的時間,增強安全性                   password = null;                System.exit(-1);              }               else {                console.printf("Invalid username or password.\n");              }              }            }    } 

摘自 qiaoning13256的專欄

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