验证用户输入的正确语法是什么？

Question

我的代码使用扫描仪创建一组运动结果，用户以这种格式输入输入“主队：客队：主队比分：客队比分” - 每个部分都拆分为数组中的字符串。如果缺少一个部分，我想创建一条错误消息，例如每个相应部分的“错误，主队似乎丢失”；

我是一个初学者，并且一直在尝试在 for 循环中放置一个 else-if 条件来帮助生成此错误消息，但是根据我收到的错误数量来判断我做错了什么（删除此标记）。

Answer 1

此代码将帮助您的程序根据您在问题中的要求验证用户输入，如果用户遗漏了任何输入，则会向他报告：

 import java.util.Scanner;

 public class Test4 {

public static void ismissing(int i)
{
    switch(i)
    {
      case 0:
      System.out.println("Home team missing");
      break;

      case 1:
      System.out.println("Away team missing");
      break;

      case 2:
      System.out.println("Home score missing");
      break;

      case 3:
      System.out.println("Away score missing");
      break;
    }
}

public static void main(String[] args) {

    Scanner scanner = new Scanner(System.in);    
    System.out.println("Input as follows; ");    
    System.out.println("Home team : Away team : Home score : Away score");
    String str=scanner.nextLine();

    String array[]=str.split(":");



    for(int i=0;i<array.length;i++)
    {
        if(array[i].equals(" "))
        {
            ismissing(i);
            System.exit(0); //will exit program if something is missing
        }
    }

        System.out.println("Correct Input");

 }

}

Answer 2

如果您要创建大量游戏，我建议您创建一个 Game 类，因为这样可以更轻松地管理 Game 对象，而不是 2 个字符串和 2 个整数值。使用Game 对象，您还可以使用Game 对象的toString 方法输出所需的字符串输出。在获取用户输入时，我使用的条件是团队名称不能为空，团队分数不能小于 0。如果用户输入为空字符串或无效整数，那么我们只需输出一条消息指示无效输入和让用户再试一次，直到他们得到有效的输入。如果您想在这种情况下退出，您可以更改它以适应用户输入无效数据时程序的正常退出。

我主要做了两种方法，一种是获取有效的 String 团队名称，另一种是获取有效的 Integer 分数。同样，如果用户输入无效数据，我们将循环直到输入有效。

游戏类：

public class Game
{
  String homeTeam = "";
  String awayTeam = "";
  int homeScore = -1;
  int awayScore = -1;

  public Game(String inHomeTeam, int inHomeScore, String inAwayTeam, int inAwayScore)
  {
    super();
    this.homeTeam = inHomeTeam;
    this.awayTeam = inAwayTeam;
    this.homeScore = inHomeScore;
    this.awayScore = inAwayScore;
  }

  @Override
  public String toString()
  {
    return homeTeam + "[" + homeScore + "] | " + awayTeam + "[" + awayScore + "]";
  }

  public String getHomeTeam() {
    return homeTeam;
  }
  public void setHomeTeam(String homeTeam) {
    this.homeTeam = homeTeam;
  }
  public String getAwayTeam() {
    return awayTeam;
  }
  public void setAwayTeam(String awayTeam) {
    this.awayTeam = awayTeam;
  }
  public int getHomeScore() {
    return homeScore;
  }
  public void setHomeScore(int homeScore) {
    this.homeScore = homeScore;
  }
  public int getAwayScore() {
    return awayScore;
  }
  public void setAwayScore(int awayScore) {
    this.awayScore = awayScore;
  }  
}

主要

public class Main
{
  static Scanner scanner = new Scanner(System.in);
  static Game[] allGames;
  static String homeTeam = "";
  static String awayTeam = "";
  static int homeScore = -1;
  static int awayScore = -1;
  static int numberOfGames = 0;

  public static void main(String[] args)
  {
    numberOfGames = GetUserInt("How many games do you want to enter - 100 or less: ");
    if (numberOfGames > 100)
      numberOfGames = 100;
    allGames = new Game[numberOfGames];

    for (int i = 0; i < numberOfGames; i++) {
      homeTeam = GetUserString("Enter the home team name: ");
      homeScore = GetUserInt("Enter the home team score: ");
      awayTeam = GetUserString("Enter the away team name: ");
      awayScore = GetUserInt("Enter the away team score: ");
      allGames[i] = new Game(homeTeam, homeScore, awayTeam, awayScore);
    }
    // output the users games
    for(Game curGame : allGames)
    {
      if (curGame != null)
        System.out.println(curGame.toString());
    }
  }

  private static String GetUserString(String prompt)
  {
    String input = "";
    while(true) {
      System.out.print(prompt);
      input = scanner.nextLine();
      if (input.length() > 0)
        return input;
      else
        System.out.println("Invalid input: Can not be empty string!");
    }
  }

  private static int GetUserInt(String prompt)
  {
    String input = "";
    while(true) {
      System.out.print(prompt);
      input = scanner.nextLine();
      if (input.length() > 0) {
        if (isValidInt(input)) {
          int value = Integer.parseInt(input);
          if (value >= 0) {
            return value;
          }
          else {
            System.out.println("Invalid input: Score can not be negative");
          }
        }
        else {
          System.out.println("Invalid input: Score must be a valid integer");
        }
      }
      else {
        System.out.println("Invalid input: Score can not be empty");
      }
    }
  }

  private static boolean isValidInt(String inString)
  {
    try {
      Integer.parseInt(inString);
      return true;
    }
    catch (NumberFormatException e) {
      return false;
    }
  }
}

希望这会有所帮助！

Answer 3

您可以做一些事情，例如使用 if 语句检查值。你可以这样说：

if(stringIsEmpty)
{
    print ("Error");
} 
else
{
   /*Keep executing program*/
}

您也可以使用 try/catch 块。这可能会有所帮助，因为如果字符串为空（空），您可以抛出空指针异常并按照您想要的方式定义它，如下所示：

try
{
    /*blank string code*/
}catch(NullPointerException e)
{
    System.out.println("Empty strings are not allowed");
}