java - 无效输入仍会更新总数

Question

[编辑]似乎将这段代码移到其他地方可以解决我的问题，但我无法弄清楚在哪里..

    if (numLeaving < MIN_PEOPLE || numEntering < MIN_PEOPLE || totalPeople < MIN_PEOPLE) { 
       JOptionPane.showMessageDialog(null,"Invalid data"); 
    }

有人可以解释为什么当我输入无效值(例如负数)时我的“总人数”仍然会更新吗？另外，如果用户输入无效输入，为什么总人数仍会被打印出来？

  final int MAX_PEOPLE = 65; 
  final int MIN_PEOPLE = 0;
  int totalPeople = 0; 
  int numLeaving = 0;
  int numEntering = 0; 
  boolean invalid = true;
  while (invalid) { 
     String question = JOptionPane.showInputDialog("leaving or entering?");          
     try  {  
        // Decrease the total if people are leaving
        if (question.equalsIgnoreCase("leaving")) {
           numLeaving = Integer.parseInt(JOptionPane.showInputDialog("number leaving:"));
           totalPeople -= numLeaving;                       
        }
        // Increase the total if people are entering
        else if (question.equalsIgnoreCase("entering")) {
           numEntering = Integer.parseInt(JOptionPane.showInputDialog("number entering:"));
           totalPeople += numEntering;                       
        }
        else {
           JOptionPane.showMessageDialog(null,"'leaving' or 'entering' only");
        }   
        // Prints out current total before capacity is exceeded          
        if (totalPeople > MAX_PEOPLE) {
           invalid = false;
           totalPeople = totalPeople - numEntering;
           JOptionPane.showMessageDialog(null,"Capacity exceeded\n" + "Total people = " + totalPeople);
        }  
        else {
           JOptionPane.showMessageDialog(null,"Total people = " + totalPeople);              
        }       
     } 
     catch (NumberFormatException e) {
        JOptionPane.showMessageDialog(null,"numbers only");
     }                        
  }

Answer 1

“totalPeople”仍在更新的原因是您没有在循环开始时检查它是否是有效输入。如果我是你，我会在 while 循环的开头添加以下代码:

if(totalPeople < 0){
   invalid = false;
   break;
}

此外，我发现将 boolean 值命名为负数有点误导。如果一个名为“invalid”的 boolean 值为 true，就会产生一个问题:“true 代表有效还是无效？”

我会将 boolean 值命名为“valid”。