使用嵌套if語句在while循環中循環的問題

Question

我遇到了程序輸出的麻煩。我已經開發了類GetInput作爲構造函數，在詢問各種輸入問題時我可以重用。每個被問到的問題都需要等於或大於最小值/小於傳遞給類/構造函數的最大值。我遇到的問題是，while循環運行時，在最終返回正確的值之前，它要求輸入四次。

我已經添加了標誌，我已經制定出來時，他們顯示。輸入後的第一個顯示是第一次添加。然後是第二次，然後是第四次。第四次它也顯示了我希望它在一次迭代中達到的標誌'結束'。 爲什麼它最終正確返回值之前循環四次？

非常感謝。這只是我第二天學習java，這讓我瘋狂。

import java.util.Scanner; //Import the scanner class 

public class main { 
public static void main(String[] args) { 

    //Set variables to hold the entry cost for each category 
    int costAccChild = 2; 
    int costUnaccChild = 5; 
    int costAdult = 10; 
    int costSenior = 8; 

    int test = GetInput(0, 1, "Enter a group? (Yes=1/No=0)"); 
    System.out.println(test); 
    System.out.println("the end"); 

} 

static int GetInput(int min, int max, String request){  
    boolean inputValid = false; //Sets default value to variable for while loop 
    int userInput = 0; //Sets default variable for input return 

    while (inputValid == false) { //Loops until receives correct input 
     System.out.println(request); //Prints question asking for input 
     Scanner inputFromUser = new Scanner(System.in); //Ask user for input 
     System.out.print("First time"); //FLAG DISPLAYS AFTER FIRST SCANNER 

     if (inputFromUser.hasNextInt() == true){ //Check if input has an integer 

      System.out.print("Second Time"); //FLAG SHOWS AFTER SECOND SCANNER 

      if (inputFromUser.nextInt() >= min && inputFromUser.nextInt() <= max){ //Check if input is valid 
       userInput = inputFromUser.nextInt(); 
       inputValid= true; 

       System.out.print("Fourth time"); //FLAG WORKS FORTH TIME 

      }else{ //Input is not correct integer, give error message 
       System.out.println("Input is not valid");   
       } 

     }else{ //Input is not an integer at all, give error message 
      System.out.println("Input is not valid"); 
     } 
    } 
    return userInput; //Returns valid input 
    } 
} 

Answer 1

從手冊頁http://docs.oracle.com/javase/6/docs/api/java/util/Scanner.html#hasNextLong()：

hasNext和next方法都可能阻塞等待進一步的輸入

它沒有循環4次，但每當你說inputFromUser.hasNextInt()或掃描儀實際上會阻止您等待您輸入值。

因此，這是很明顯，你必須修復

Answer 2

你應該存儲輸入某些變量，然後他們在if條件比較的錯誤。

這不會阻止輸入以進一步輸入。

試試這個：

public static void main(String[] args) { 

    //Set variables to hold the entry cost for each category 
    int costAccChild = 2; 
    int costUnaccChild = 5; 
    int costAdult = 10; 
    int costSenior = 8; 

    int test = GetInput(0, 1, "Enter a group? (Yes=1/No=0)"); 
    System.out.println("Return Result: " + test); 
    System.out.println("The end"); 

} 

static int GetInput(int min, int max, String request) { 
     boolean inputValid = false; //Sets default value to variable for while loop 
     int userInputMin = 0, userInputMax=0; //Sets default variable for input return 

     while (inputValid == false) { //Loops until receives correct input 
      System.out.println(request); //Prints question asking for input 
      Scanner inputFromUser = new Scanner(System.in); //Ask user for input 
      System.out.print("First time: "); //FLAG DISPLAYS AFTER FIRST SCANNER 

      if (inputFromUser.hasNextInt() == true) { //Check if input has an integer 
       userInputMin = inputFromUser.nextInt(); 
       System.out.print("Second Time: "); //FLAG SHOWS AFTER SECOND SCANNER 
       if (inputFromUser.hasNextInt() == true) { //Check if input has an integer 
        userInputMax = inputFromUser.nextInt(); 
        if (userInputMin >= min && userInputMax <= max) { //Check if input is valid 

         inputValid = true; 

         System.out.println("Third time"); //FLAG WORKS Third Time 

        } else { //Input is not correct integer, give error message 
         System.out.println("Input is not valid"); 
        } 
       }  
      } else { //Input is not an integer at all, give error message 
       System.out.println("Input is not valid"); 
      } 
     } 
     return userInputMin; //Returns valid input 
    }