在while循環中測試條件，然後在Java中退出while循環

Question

我是Java新手，我試圖理解如何在for循環中嵌套if語句，並在if語句後退出for循環被執行。我有一個數組，for循環遍歷數組以查看ID是否存在，是否應該刪除它，如果它不存在，那麼它應該打印一條錯誤消息。發生的情況是條件是在while循環中的嵌套if語句中進行測試並打印錯誤消息3次。我希望它只打印一次錯誤消息。

在我的主要方法，我在第一個它應該只是刪除ID和打印，這是REM，第二個它應該只打印錯誤信息一旦有

remove("3"); 
remove("3"); 

。這是一個針對學校的項目，不需要用戶輸入。我只是想了解如何使這項工作不打印出重複的錯誤消息

public static void remove(String studentID) 
{ 

    for (int i = 0; i < thestudents.size(); i++) 
    { 

     Student temp = thestudents.get(i); 

     if (temp.getStudentID()==(Integer.parseInt(studentID))) 
     { 
      thestudents.remove(i); 
      System.out.println("Student " + temp.getFirstName() + " was removed"); 
     } 
     else 
     { 
      System.out.println("Student with ID " + studentID + " Was not found!"); 
     } 
    } 
} 

結果：

 
Student with ID 3 Was not found! 
Student with ID 3 Was not found! 
Student Jack was removed 
Student with ID 3 Was not found! 
Student with ID 3 Was not found! 
Student with ID 3 Was not found! 
Student with ID 3 Was not found! 
Student with ID 3 Was not found! 

後市展望：

 
Student Jack was removed 
Student with ID 3 Was not found! 

Answer 1

只要添加一個休息將在比賽結束後刪除輸出，但比賽前的輸出將保持不變。

我想你想擺脫所有的假陰性輸出。

因此，您必須在循環（刪除else行）後移動負輸出（else塊的內容），並確保在找到ID時不會執行此代碼。

執行此操作的最佳方法是在if塊中添加return作爲最後一條語句。

for (int i = 0; i < thestudents.size(); i++) 
{ 
    Student temp = thestudents.get(i); 
    if (temp.getStudentID()==(Integer.parseInt(studentID))) 
    { 
     thestudents.remove(i); 
     System.out.println("Student " + temp.getFirstName() + " was removed"); 
     return; // leaving the method whe ID found 
    } 
} 
// is only executed when ID not found 
System.out.println("Student with ID " + studentID + " Was not found!)"; 

Answer 2

只需添加一個break內if聲明。如果if陳述是true，那麼循環將終止。

if (temp.getStudentID()==(Integer.parseInt(studentID))) { 
    hestudents.remove(i); 
    System.out.println("Student " + temp.getFirstName() + " was removed"); 
    break; 
} 

Answer 3

你可以使用一個break語句來終止循環，或者更好的是，一個return聲明中以完全終止方法一旦你找到合適的項目：

public static void remove(String studentID) 
{ 

    for (int i = 0; i < thestudents.size(); i++) 
    { 

     Student temp = thestudents.get(i); 

     if (temp.getStudentID()==(Integer.parseInt(studentID))) 
     { 
      thestudents.remove(i); 
      System.out.println("Student " + temp.getFirstName() + " was removed"); 
      return; 
     } 
    } 

    // If we get here it means we haven't returned, so the student wasn't found 
    System.out.println("Student with ID " + studentID + " Was not found!"); 
}