我如何限制 Java 中的“新掃描儀（System.in）”系統，不進一步處理用戶輸入數據，除非它是正確的輸入值？

Question

我正在學習 Java，並且我的知識有所提高。 我希望應用程序根據用戶輸入的值走得更遠，前提是它是正確的，否則我希望相同的問題（控制台輸入）自行重復（不使用應用程序走得更遠），直到用戶輸入正確的價值！ 我的代碼如下所示：

package oop.project;

import java.util.Scanner;

/**
 *
 * @author Dragos
 */
public class OOPProject {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        Scanner sc = new Scanner(System.in);
        Car Honda = new Car(2018, 20000, "Honda", "Civic", 200, 6, 0, 0);
        System.out.println("Manufacturer is: " + Honda.maker + ", model: " + Honda.model + 
                           ", year of fabrication: " + Honda.year + ", price: " + Honda.price + 
                           "!");
        System.out.println("Please start the engine of your vehicle, by typing in 'Yes' or 'Start' 
                           or 'Turn on'!");
        System.out.print("Do you wish to start the engine?");
        System.out.println(" ");
        Honda.StartEngine(sc);
}

構造函數類及其功能：

public class Car {

    public int year;
    public int price;
    public String maker;
    public String model;

    public int maximumSpeed;
    public int numberOfGears;
    public int currentSpeed;
    public int currentGear;
    public boolean isEngineOn;

    public Car(int year, int price, String maker, String model, int maximumSpeed,
               int numberOfGears, int currentSpeed, int currentGear) {
        this.year = year;
        this.price = price;
        this.maker = maker;
        this.model = model;
        this.maximumSpeed = maximumSpeed;
        this.numberOfGears = numberOfGears;
        this.currentSpeed = currentSpeed;
        this.currentGear = currentGear;
    }

    public String StartEngine(Scanner in) {
        String input = in.nextLine();
        do{
            isEngineOn = true; 
        } while(input.equals("Yes") || input.equals("Start") || input.equals("Turn on"));

        if(isEngineOn) {
            System.out.println("Engine is on!");
        } else {
            System.out.println("Your input is not correct! Please start the engine!");
            isEngineOn = false;
        }  
        return input;
    }

在 do & while 之前，我只有 if-else 語句與(input.equals("Yes") || input.equals("Start") || input.equals("Turn on"))在 if語句，但不管用戶在 IDE 控制台中輸入了錯誤的單詞這一事實，該應用程序無論如何都會繼續前進，當輸入錯誤的單詞時，它確實會顯示正確的消息，但不會停止或限制用戶輸入正確的值！ 試圖通過添加 do-while 語句來限制用戶輸入正確的值，但效果不佳。

Answer 1

在獲得有效輸入之前，您必須處於循環狀態。 試試下面的片段。

while(in.hasNext()) {
    String input = in.nextLine();
    if(input.equals("Yes") || input.equals("Start") || input.equals("Turn on")) {
        System.out.println("Engine is on!");
        break;
    } else {
        System.out.println("Your input is not correct! Please start the engine!");
    }
}

如果你想從函數中返回輸入，你可以像下面那樣做。

while (in.hasNext()) {
    String input = in.nextLine();
    if (input.equals("Yes") || input.equals("Start") || input.equals("Turn on")) {
        System.out.println("Engine is on!");
        return input;
     } else {
        System.out.println("Your input is not correct! Please start the engine!");
     }
}
return null;

Answer 2

    while(!isEngineOn) {
      String input = in.nextLine();
      isEngineOn = input.equals("Yes") || input.equals("Start") || input.equals("Turn on"));
      if (!isEngineOn) System.out.println("Your input is not correct! Please start the engine!");
    }

或者像這樣，如果你以后需要答案：

    String input;
    while(!isEngineOn) {
      input = in.nextLine();
      isEngineOn = input.equals("Yes") || input.equals("Start") || input.equals("Turn on"));
      if (!isEngineOn) System.out.println("Your input is not correct! Please start the engine!");
    }