java - 无法实现检测输入是否为整数的系统

Question

我正在尝试创建一个系统，询问用户他们希望一个短语重复多少次，然后它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，它会变得很糟糕。

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.");
        } 

每当我尝试任何事情时，它都会询问我想要哪个短语以及我想要重复多少次。然后程序就停止了，无论我输入一个整数还是一个字符串，它都没有给我任何其他提示。

输出是这样的：

你想重复哪个短语？测试 你想要多少测试？3

就是这样。

标签： javainputinteger

Answer 1

首先，只需使用一个 Scanner 对象。您不需要更多的键盘输入。

如果你愿意，你可以坚持使用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()方法与一个小的正则表达式(RegEx) 一起使用。"\\d"传递给matches()方法的表达式检查它所处理的字符串是否包含所有（1 个或多个）数字。

但是，如果您一心想要使用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.