java - 在实现检测输入是否为整数的系统时遇到困难

Question

我正在尝试创建一个系统，询问用户希望某个短语重复多少次，然后检查答案是整数还是字符串。当我不尝试实现这个系统并让它只询问该短语以及应该重复多少次时，该程序运行良好，但当我尝试检查次数是否为整数时，该程序崩溃了。

import java.util.*;

public class Phrase {
    public static Scanner phraseScan = new Scanner (System.in);
    public static Scanner amountScan = new Scanner (System.in);
    public static void main (String[] args ) {

        System.out.println("What phrase do you want repeated?");
        String phrase = phraseScan.nextLine();
        int phraseLoops = 0;

        System.out.println("How many " + phrase + "s" + " do you want?");
        int desiredPhraseLoops = amountScan.nextInt();

        for (;;) {
            if (!amountScan.hasNextInt()) {
                System.out.println("Integers only please");
                amountScan.next();

            }
            desiredPhraseLoops = amountScan.nextInt();
            if (desiredPhraseLoops >= 0) {
                System.out.println("Valid amount!");
                continue;
            } else {
                break;

            }
        }



        System.out.println(desiredPhraseLoops + " " + phrase + "s coming your way!");

        do {
            System.out.println(phrase);
            phraseLoops++;

        } while (phraseLoops != desiredPhraseLoops);

        System.out.println("You printed " + phraseLoops + " " + phrase + "s" );
    }
}

我尝试过的:

try {
          desiredPhraseLoops = amountScan.nextInt();

        } catch (InputMismatchException exception) {
            System.out.println("This is not an integer.");
        } 

          if (!amountScan.hasNextInt()) {
            System.out.println("Good.");
        } else {
            System.out.println("Enter an Integer please.");
        } 

每当我尝试任何操作时，它都会询问我想要哪个短语以及我希望它重复多少次。然后程序就停止了，无论我输入整数还是字符串，它都没有给我任何其他提示。

输出是这样的:

您想要重复哪个短语？测试您想要多少次测试？3

就是这样。

Answer 1

首先，只需使用一个 Scanner 对象。您不需要更多的键盘输入。

如果您愿意，可以继续使用 Scanner#nextLine() 方法，例如:

Scanner userInput = new Scanner(System.in); 

String phrase = "";
while (phrase.equals("")) {
    System.out.println("What phrase do you want repeated?");
    phrase = userInput.nextLine();
    // VALIDATION: 
    // Was anything other than a empty string (spaces) 
    // or longer than 2 characters supplied?
    if (phrase.trim().equals("") || phrase.length() < 3) {
        // Nope!
        System.err.println("Invalid Input!. Enter a proper phrase!");
        phrase = "";
    }
    // Yes, allow the prompt loop to exit.
}

String phraseLoopsNumber = "";
while (phraseLoopsNumber.equals("")) {
    System.out.println("How many " + phrase + "s" + " do you want?");
    phraseLoopsNumber = userInput.nextLine();
    // VALIDATION: 
    // Did the User supply a string representation of an integer value? 
    if (!phraseLoopsNumber.matches("\\d+")) {
        // Nope!
        System.out.println("Invalid Input (" + phraseLoopsNumber + ")! An integer value is expected!");
        phraseLoopsNumber = "";
    }
    // Yes he/she/it did...Allow prompt loop to exit.
}

int numberOfLoops = Integer.parseInt(phraseLoopsNumber);

// Do what you have to do with the desired number of loops contained
// within the numberOfLoops integer variable.

在上面的代码中，String#matches()方法与一个小Regular Expression一起使用(正则表达式)。传递给 ma​​tches() 方法的 "\\d" 表达式会检查它所处理的字符串是否包含所有(1 个或更多)数字。

如果您执意要使用 Scanner#nextInt() 方法，那么您可以这样做:

int numberOfLoops = -1;
while (numberOfLoops == -1) {
    System.out.println("How many " + phrase + "'s" + " do you want?");
    // Trap any input errors against the Scanner.nextInt() method... 
    // This would be a form of validation.
    try {
        numberOfLoops = userInput.nextInt();
        // Consume the newline from ENTER key in case a nextLine() prompt is next.
        userInput.nextLine(); 
    } catch (Exception ex) {
        System.out.println("Invalid Input! An integer value is expected!");
        // Consume the newline from ENTER key in case a nextLine() prompt is next.
        // The first one above would of been skipped past if nextInt() threw an exception.
        userInput.nextLine(); 
        numberOfLoops = -1;
        continue;  // continue loop so as to re-prompt
    }
    // Further Validation: 
    // Did the User supply a number greater than 0? 
    if (numberOfLoops < 1 ) {
        // Nope!
        System.out.println("Invalid Input (" + numberOfLoops + ")! A value 1 or greater is expected!");
        numberOfLoops = -1; 
    }
    // Yes he/she did...Allow prompt loop to exit.
}
// Do what you have to do with the desired number of loops contained
// within the numberOfLoops integer variable.