我如何限制 Java 中的“新扫描仪（System.in）”系统，不进一步处理用户输入数据，除非它是正确的输入值？

Question

我正在学习 Java，并且我的知识有所提高。 我希望应用程序根据用户输入的值走得更远，前提是它是正确的，否则我希望相同的问题（控制台输入）自行重复（不使用应用程序走得更远），直到用户输入正确的价值！ 我的代码如下所示：

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);
}

构造函数类及其功能：

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 语句与(input.equals("Yes") || input.equals("Start") || input.equals("Turn on"))在 if语句，但不管用户在 IDE 控制台中输入了错误的单词这一事实，该应用程序无论如何都会继续前进，当输入错误的单词时，它确实会显示正确的消息，但不会停止或限制用户输入正确的值！ 试图通过添加 do-while 语句来限制用户输入正确的值，但效果不佳。

Answer 1

在获得有效输入之前，您必须处于循环状态。 试试下面的片段。

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!");
    }
}

如果你想从函数中返回输入，你可以像下面那样做。

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!");
    }

或者像这样，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!");
    }