4

我以两种不同的Scanner.nextLine()方法从两个不同的扫描仪对象调用该方法。有时当我Scanner.nextLine()从第二种方法调用时，它会给我一个“行不可用”错误。可能是什么问题？

import java.util.Scanner;

public class TicTacToe {

    private final String COMPUTER = "computer";
    private final String PLAYER = "player";

    /**
     * Asks the user to choose a letter ('X' or 'O')
     * and checks if the input is valid.
     */
    public void askLetter() {
        System.out.println("Please enter 'X' or 'O': ");
        Scanner input = new Scanner(System.in);
        String letter = input.nextLine().toUpperCase().trim();
        while (!letter.equals("X") && !letter.equals("O")) {
            System.out.println("Please enter 'X' or 'O': ");
            letter = input.nextLine().toUpperCase().trim();
        }
        input.close();
    }


    /**
     * Asks the user to choose who goes first. 
     * @return 'computer' or 'player'
     */
    public String decide() {
        //System.out.println("Choose who goes first('player' or 'computer'): ");
        Scanner input = new Scanner(System.in);
        String first = input.nextLine().toUpperCase().trim();
        while (!first.equals(COMPUTER) && !first.equals(PLAYER)) {
            System.out.println("Choose who goes first('player' or 'computer'): ");
            first = input.nextLine().toUpperCase().trim();
        }
        input.close();
        return first;
    }

    public static void main(String[] args) {
        TicTacToe tictac = new TicTacToe();
        tictac.askLetter();
        tictac.decide();
    }
}
4

1 回答 1

10

您的askLetter方法关闭了扫描仪......这将关闭System.in。然后，您尝试System.in在decide.

将构造函数更改为接受Scanner您在 中创建的main。然后将该扫描仪保留在一个字段中并在两种方法中使用它：

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    TicTacToe tictac = new TicTacToe(scanner);
    tictac.askLetter();
    tictac.decide();
    // You might want to close the scanner here, but you don't really have to.
}

这也有助于使您的代码更具可测试性——您现在可以使用Scanner由假数据支持的 a （例如 a StringReader）。

于 2013-05-17T17:20:12.583 回答