Java- 带有包含默认情况的 switch 语句的 For 循环。我怎样才能让默认情况下只打印一次输出？答案

【问题标题】：Java- For loop with a switch statement containing default case. How can I get the default case to print the output only once?Java- 带有包含默认情况的 switch 语句的 For 循环。我怎样才能让默认情况下只打印一次输出？
【发布时间】：2015-10-11 18:27:04
【问题描述】：

下面的默认语句完全符合它的预期：捕获上述情况中未提及的所有字符，并通知我（通过字符串后），有一个无效的字符进入那里的某个地方。但是，如果有两个无效字符： println 语句将打印两次。如果有三个：三次，等等。在一个 100,000 个字符的字符串中，多次打印该行将是低效的。

无论有多少无效字符，我如何才能让它只打印一次被输入？请提前告知并感谢您帮助 Java 新手！

  //for loop to calculate how many A's, G's, T's, and C's in the string
  //default statement at the end of the switch statements to weed out 
  //invalid characters. 
  for(int i=0; i < length; i++)
  {
     ch = dna.charAt(i);
     switch (ch)    
     {
        case 'A':   aCount++;
                    break;
        case 'C':   cCount++;
                    break;
        case 'G':   gCount++;
                    break;
        case 'T':   tCount++;
                    break;
        default: 
           System.out.println("An invalid character was entered.");
     }
  }

【问题讨论】：

如果您想在遇到无效字符后继续计数：引入一个布尔标志，指示您是否已经看到无效字符...

标签： java for-loop switch-statement default

【解决方案1】：

 import java.util.Scanner;
 //done by Nadim Baraky
 //this program calculates the number of A's, C's, G's & T's;
 //it prints a statement once as you wished in case invalid characters where entered

public class ACGT_DNA {


  public static void main (String[] args) {
     //the counter is set to be 1;
     int length, counter=1; 
     int aCount =0, cCount=0, gCount =0, tCount=0;

     char ch;

     Scanner scan = new Scanner(System.in);
     System.out.print("Enter your string: ");
     String dna = scan.next();
     scan.close();
     length = dna.length();


 for(int i=0; i < length; i++) {
    ch = dna.charAt(i);

    switch (ch) {

      case 'A':   aCount++; 
                  break;
      case 'C':   cCount++;
                  break;
      case 'G':   gCount++;
                  break;
      case 'T':   tCount++;
                  break;
      default: 
         if(counter==1) { 
             System.out.println("An invalid character was entered.");
             counter++;
             //after counter is being incremented, the if statement won't be true; so no matter how invalid characters you enter, the statement will be just be printed once.
         }

    }
}

    System.out.println("A's " + aCount);
    System.out.println("C's " + cCount);    
    System.out.println("G's " + gCount);    
    System.out.println("T's " + tCount);

}

}

【讨论】：