java - if-else语句去错误的条件语句java？

Question

我的程序输入似乎在 if-else 语句中转到了错误的 else 语句。

import java.util.Scanner;
import java.text.*;

public class CSCD210Lab6
{
   public static void main (String [] args)
   {
     Scanner waterInput = new Scanner(System.in);
     DecimalFormat df = new DecimalFormat("$#,###.00"); 
     DecimalFormat zf = new DecimalFormat("#,###.0"); 

      //declare variables
      int beginMeter, endMeter;
      String customerCode;
      double billingAmount,gallonsUsed;


      billingAmount = 0;

      System.out.print("Please Enter Your Customer Code: ");
      customerCode = waterInput.next();
      System.out.print("Please Enter Your Beginning Meter Reading: ");
      beginMeter = waterInput.nextInt();
         if(beginMeter < 0)
         {
            System.out.println();
            System.out.print("ERROR! You Have Entered A Negative Number. The Program Will Now Close.");
            System.exit(0);
         }

      System.out.print("Please Enter Your Ending Meter Reading: ");
      endMeter = waterInput.nextInt();
         if(endMeter < 0)
         {
            System.out.println();
            System.out.print("ERROR! You Have Entered A Negative Number. The Program Will Now Close.");
            System.exit(0);
         }
      if(endMeter > beginMeter)
      {
        gallonsUsed = ((double)endMeter - beginMeter)/10;
      }
      else
      {
         gallonsUsed = (1000000000-((double)beginMeter - endMeter))/10; 
      }
      if (customerCode.equals("r")||customerCode.equals("R"))
      {
         billingAmount = 5.00 + (.0005 * gallonsUsed);
      } 

      if(customerCode.equals("c")||customerCode.equals("C") && gallonsUsed <= 4000000)      
      {
         billingAmount = 1000.00;
      }

      if(customerCode.equals("c")||customerCode.equals("C") && gallonsUsed > 4000000)
      {
        billingAmount = 1000.00 + ((gallonsUsed-4000000) * 0.00025);
      }

      if(customerCode.equals("i")||customerCode.equals("I")&& gallonsUsed <= 4000000)
      {
         billingAmount = 1000.00;
      }

      if(customerCode.equals("i")||customerCode.equals("I")&& gallonsUsed > 4000000 && gallonsUsed < 10000000)
      {
         billingAmount = 2000.00;
      }
      if(customerCode.equals("i")||customerCode.equals("I")&& gallonsUsed >= 10000000) 
      {
         billingAmount = 2000.00 +(gallonsUsed * .00025);
      }


      System.out.println();
      System.out.print("Your Customer Code is: "+customerCode); 
      System.out.println();
      System.out.print("Your Beginning Meter Reading is: "+beginMeter); 
      System.out.println();
      System.out.print("Your Ending Meter Reading is: "+endMeter);
      System.out.println();
      System.out.print("You Have Used "+zf.format(gallonsUsed)+" Gallons During This Billing Period.");
      System.out.println();
      System.out.print("Your Bill is: "+df.format(billingAmount));
      System.out.println();
      System.out.println();
      System.out.print("Please Pay Promptly. We Detest Late Accounts.");



   }
}

例如，如果我输入 c，并且总用水量少于 4,000,000 加仑，则当总用水量超过 4,000,000 加仑时，它会执行该行代码。为什么？

Answer 1

由于条件的运算顺序

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html

customerCode.equals("c")||customerCode.equals("C") && 已用加仑 <= 4000000

T || F&&F

这等于 true，因此 billingAmount = 1000.00；

但是下一个语句是

customerCode.equals("c")||customerCode.equals("C") && 加仑已使用 > 4000000)

T || F&&F

这也等于 true，因此 billingAmount 被覆盖 - billingAmount = 1000.00 + ((gallonsUsed-4000000) * 0.00025);

这两个 if 语句都适合您的情况。

要修复，请使用括号。并且还使用 else 语句。当第一个条件检查之一为真时，没有理由进行无数的条件检查。