行代碼打印dublicates

case 2: 
    System.out.println("Please enter Book ID: "); 
    String userinput2 = sc.next(); 
    for (int i = 0; i < myBooks.size(); i++) { 
     if (myBooks.get(i).getBookID().contains(userinput2)) { 
      System.out.println("BookID: " + myBooks.get(i).getBookID() + "\nTitle: " 
        + myBooks.get(i).getTitle() + "\nAuthor: " + myBooks.get(i).getAuthor()); 
      System.out.println("Please enter new details of book"); 
      System.out.println("Title: "); 
      String userinput7 = sc.next(); 
      myBooks.get(i).setTitle(userinput7); 
      System.out.println("Author: "); 
      String u1 = sc.next(); 
      myBooks.get(i).setAuthor(u1); 
      myBooks.get(i).setOnLoan(false); 
      myBooks.get(i).setNumLoans(0); 
      System.out.println("---------------------------------------------------"); 
      System.out.println("The book has been successfully updated"); 
      System.out.println("Book ID: " + myBooks.get(i).getBookID() + " " + "\nTitle: " 
        + myBooks.get(i).getTitle() + " " + "\nAuthor: " + myBooks.get(i).getAuthor()); 
      System.out.println("---------------------------------------------------"); 
     } 
     else { System.out.println("Please enter a correct bookID"); 
     } 
    }

//我的驗證檢查有問題。如果用戶輸入不存在的bookID，而不是打印出「請輸入正確的bookID」一次，它將打印出4次，這相當於我在數組列表中的對象數量。有沒有辦法對此進行分類？行代碼打印dublicates

來源

2015-12-03 JC1

考慮提供一個[可運行示例]（HTTPS ：//stackoverflow.com/help/mcve）它演示你的問題。這不是代碼轉儲，而是您正在做的事情的一個例子，它突出了您遇到的問題。這會減少混淆和更好的反應。 – MadProgrammer

在添加任何新項目之前，您應該首先檢查重複項 – MadProgrammer

並且在else執行後您也不允許用戶再次輸入，因此它會一直執行直到循環結束。嘗試在'else'塊中添加'userinput2 = sc.next（）;'或許。 –

你else語句中的中間爲聲明

for (int i = 0; i < myBooks.size(); i++) { 
     if (myBooks.get(i).getBookID().contains(userinput2)) { 
      [[do stuff]] 
     } 
     else { System.out.println("Please enter a correct bookID"); 
     } 
}

它看起來應該是在中間的if語句

if (myBooks.get(i).getBookID().contains(userinput2)) { 
    for (int i=...) { 
     [[do stuff]] 
    } 
} 
else { System.out.println("Please enter a correct bookID"); 
}

來源

2015-12-03 02:30:40

行代碼打印dublicates

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