搜索Java ArrayList並返回元素位置 - indexOf（）不起作用。

Question

我一直在編寫一個程序，要求用戶輸入名稱，票據類型和罰款。用戶輸入被存儲到文本文件中。我正在將文本文件讀入名爲「list」的數組中，並提示用戶搜索「關鍵字」。我將關鍵字存儲爲String =關鍵字。當我使用println（list.indexOf（關鍵字））時，即使正在搜索的關鍵字正在返回，我也會得到一個「-1」輸出！這就是我被卡住的地方......我不確定爲什麼indexOf（）方法找不到該元素，但是我的搜索關鍵字能夠。任何幫助將不勝感激！注意：我的最終目標是搜索「關鍵字」，找到元素位置並返回true。然後，我會問用戶一個新的名稱，票類型和罰款。我將替換文本文件中的信息並將新信息寫入前面提到的文本文件。預先感謝您的意見。包含代碼（我是Java新手，所以請保持良好：0）完成程序後，我將清理代碼。

import java.util.*; 
import java.io.*; 
import java.text.Collator; 
public class Project { 

public static void main(String[] args) throws IOException { 

String name = ""; 
String ticketType = ""; 
double fine = 0; 
char quit; 
boolean cont = true; 

while (cont){ 
do { 
    //Create file Project.txt 
    PrintStream out = new PrintStream(new FileOutputStream("Project.txt", true)); 
    Scanner input = new Scanner(System.in); 
    //Prompt user to enter name, ticket type, fine or 'q' if done 
    System.out.println("Name:"); 
    name = input.nextLine(); 
    System.out.println("Ticket Type:"); 
    ticketType = input.nextLine(); 
    System.out.println("fine:"); 
    fine = input.nextDouble(); 
    System.out.println("press 'q' if you are done entering or 'c' to continue entering"); 
    quit = input.next().toLowerCase().charAt(0); 
    //Write user input to Project.txt file 
     out.print(name + ", "); 
     out.print(ticketType + ", "); 
     out.printf("%.2f",fine); 
     out.println(); 
     out.close(); 
} 
while (!(quit == 'q'));{ 
    System.out.println("done"); 
} 
Scanner input = new Scanner(System.in); 
System.out.println("are you sure youre done"); 
System.out.println("enter y to if your done, n to enter more"); 
char Continue = input.next().toLowerCase().charAt(0); 
//Prompt user in the are done entering 
//If 'y', program moves on. If 'n' loop back to beginning 
if (Continue == ('y')){ 
    cont = false; 
    } 
//Done entering names to list 
//Now read in file to array and sort alphabetically 

} 
Scanner readArray = new Scanner(new File("Project.txt")); 
    ArrayList<String> list = new ArrayList<String>(); 
    while (readArray.hasNext()){ 
     list.add(readArray.nextLine().toLowerCase()); 
    } 
    readArray.close(); 
    Collections.sort(list, Collator.getInstance()); //sort array alphabetically 
    //print array as list comma separated 
    for (String value : list){ 
     System.out.println(value); 
    } 
    //Prompt user to enter a name they want to search for 
    Scanner search = new Scanner(System.in); 
    System.out.println("search keyword: "); 
    String keyword = search.next().toLowerCase(); 
    System.out.println("searching for: " + keyword); 
    //Search array 'list' for user input 
    boolean found = false; 
    for (String value : list) { 
     if (value.contains(keyword)) { 
     found = true; 
     } 
    } 
    if (found) { 
     System.out.println("found"); 
     System.out.println(list.indexOf(keyword)); 

    } 
    else { 
     System.out.println(" not found"); 
    } 

    } 

} 

Answer 1

如果你想通過你搜索你可以得到該指數在相同的點是你當前設置的布爾發現，真正讓您找到的元素的索引：

Integer foundIndex = null; 
for (String value : list) { 
    if (value.contains(keyword)) { 
     foundIndex = list.indexOf(value); 
     break; // we stop iteration because we got our result 
    } 
} 

boolean found = (foundIndex!=null); 
if (found) { 
    //.... 
} else { 
    //.... 
} 

Answer 2

如果正確地理解你的問題，那麼下面的代碼將幫助您

list.add("for example") 
list.add("for") 
list.add("example") 
System.out.println(list.indexOf("for example")) 
System.out.println(list.indexOf("for")) 
System.out.println(list.indexOf("example")) 

的indexOf不搜索在元素的關鍵字。它搜索等於傳入參數的元素索引。