java - 想要循环但变量未初始化

Question

我的问题从第一个 do-while 循环开始。我希望它询问“请输入 0 到 90 之间的角度:”，如果用户确实输入 0 到 90 之间的数字，则必须输入火药的量。他们的输入将经过物理计算，如果他们的结果不是“它很成功!”然后我要他们回去再次输入角度和火药。但问题在于

while (距离 - 距离2 != 0 || 距离 - 距离2 != 1 || 距离2 - 距离!= 1); System.out.println("成功了!");

The error says: variable distance2 might not have been initialized.

<小时/>

    import java.util.*;
    import java.text.*;
    public class BombsAway {
    private static double ZERO_THOUSAND = 1000;
    private static double KG_TO_VELOCITY = 50;
    private static double GRAVITY = -9.81;
    public static void main(String[] args) {

      Scanner input = new Scanner(System.in);
      DecimalFormat threeDec = new DecimalFormat("#.##");
      Random gen = new Random();
      BombsAway distanceAn = new BombsAway();
      boolean invalidInput = true;
      double distance, distance2;

      System.out.println("Please enter a positive integer seed value: ");
      while(invalidInput) {
         try {
            int seedValue = Integer.valueOf(input.nextLine());
            if (seedValue <= 0) {
               System.out.println("Please enter a positive integer seed value:"
                + " ");
            } 
            else {
               distance = gen.nextDouble() * ZERO_THOUSAND;
               System.out.println("That target is " + threeDec.format(distance) 
                + "m away.");  
               do {
               System.out.println("Please enter an angle between 0 and 90 " +
                "degrees: ");
               while (invalidInput) {
                  try {
                     double angle = Double.valueOf(input.nextLine());
                     if (angle < 0 || angle > 90) {
                        System.out.println("Please enter an angle between " +
                         "0 and 90 degrees: ");
                     } 
                     else {
                        System.out.println("Please enter the amount of " + 
                         "gunpowder in kilograms: ");
                        try {
                           double gunpowder = 
                            Double.valueOf(input.nextLine());
                           //physics part
                           double initialV = gunpowder * KG_TO_VELOCITY;
                           double vX = initialV * Math.cos(angle);
                           double vY = initialV * Math.sin(angle);
                           double airBorn = (-vY - vY) / GRAVITY;
                           distance2 = (vX * airBorn);

                           if (distance > distance2) {
                              double finalDist = distance - distance2;
                              System.out.println("It's " +
                               threeDec.format(finalDist) + "m short.");
                           }
                           else if (distance < distance2) {
                              double finalDist = distance2 - distance;
                              System.out.println("It's " + 
                               threeDec.format(finalDist) + "m long.");
                           }
                        }
                        catch(NumberFormatException e) {
                           System.out.println("Please enter the amount of " +
                            "gunpowder in kilograms: ");
                        }
                     }
                  }
                  catch(NumberFormatException e) {
                      System.out.println("Please enter an angle between " +
                       "0 and 90 degrees: ");
                  }
               }
            }while (distance - distance2 != 0 || distance - distance2 != 1
              || distance2 - distance != 1);
                System.out.println("It's a hit!");
            }
         }
         catch(NumberFormatException e) {
            System.out.println("Please enter a positive integer seed value: ");
         }
      }
   }
}

Answer 1

在您的代码中 - distance2 在条件 block 之一(在 while 循环内的 else block 中)初始化，可能存在以下情况:您的 while 或 else 条件将无法满足，在这种情况下，distance2 未初始化，并且局部变量无法在没有初始化的情况下使用，因此只需使用任何有意义或所需的默认值初始化 distance2 即可:

double distance2 = 0.0; 或使用代码逻辑适用的某个特定值