为什么以下代码会给我一个运行时错误?第二次调用该方法时,它给了我一个NoSuchElementException。如果删除对stdin.close()的调用,效果很好,但是Eclipse发出警告,指出资源未关闭。

码:

import java.util.Scanner;


public class st {
  public static void main(String[] args) {
    System.out.println("First call");
    getInt("Enter first int (1-10): ");
    System.out.println("Second call");
    getInt("Enter second int (1-10): ");
  }

  /**
   * Reads an integer number from the keyboard.
   *
   * @param  prompt    the string to display as a prompt.
   * @return           the integer number entered at the keyboard.
   */
  public static int getInt(String prompt) {
    Scanner stdin = new Scanner(System.in);

    System.out.print(prompt);
    int val = stdin.nextInt();

    stdin.close();
    return(val);
  }
}

// END


输出:

>java st
First call
Enter first int (1-10): 5
Second call
Enter second int (1-10): Exception in thread "main" java.util.NoSuchElementException
        at java.util.Scanner.throwFor(Unknown Source)
        at java.util.Scanner.next(Unknown Source)
        at java.util.Scanner.nextInt(Unknown Source)
        at java.util.Scanner.nextInt(Unknown Source)
        at st.getInt(st.java:24)
        at st.main(st.java:9)

>


版:

>java -version
java version "1.7.0_21"
Java(TM) SE Runtime Environment (build 1.7.0_21-b11)
Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)

>


谢谢

布赖恩

最佳答案

就像@MikePrecup所说的那样,当您关闭第一个扫描仪(stdin)时,您也正在关闭System.in,因此第二个扫描仪无法再读取它,并且会抛出NoSuchElementException

但是,我建议另一个选择:使用单个扫描程序将其声明为类变量。

public class st {

  private static Scanner stdin = new Scanner(System.in);

  public static void main(String[] args) {
    System.out.println("First call");
    getInt("Enter first int (1-10): ");
    System.out.println("Second call");
    getInt("Enter second int (1-10): ");
  }

  /**
   * Reads an integer number from the keyboard.
   *
   * @param  prompt    the string to display as a prompt.
   * @return           the integer number entered at the keyboard.
   */
  public static int getInt(String prompt) {
    System.out.print(prompt);
    int val = stdin.nextInt();

    stdin.close();
    return(val);
  }
}

// END

09-09 22:23