如何使用 (.contains) 从数组列表中查找特定字符串

Question

I need to find a specific string (letter) from an array list. I have used the.add function to add a list I have created previously into my array. How do I (using my array list) find a specific word with a particular letter that the user has typed in.

import java.util.*;

public class Library {  
    
    public static void main (String[] args)
    {
        
        
        ArrayList<Book> bookList = new ArrayList<Book>();
        ArrayList<libraryMembers> memberList = new ArrayList<libraryMembers>();
        
        
    String userChoice;
    
    {   
        
        //Using previous class and assigning values to ID, Phone, Name, and Surname
        libraryMembers lm1 = new libraryMembers (1111, 3234231, "Glock", "John");
        libraryMembers lm2 = new libraryMembers (1112, 3234231, "Ackerman", "Mikasa");
        libraryMembers lm3 = new libraryMembers (1113, 341231, "Crab", "Armin");
        libraryMembers lm4 = new libraryMembers (1114, 3423431, "Bacony", "Conny");
        libraryMembers lm5 = new libraryMembers (1115, 3423431, "Jaeger", "Erwin");
        libraryMembers lm6 = new libraryMembers (1116, 3423431, "Jaeger", "Zeke");
        
        //Printing member information
        lm1.informationPrint();
        lm2.informationPrint();
        lm3.informationPrint();
        lm4.informationPrint();
        lm5.informationPrint();
        lm6.informationPrint();
            
        
        memberList.add(lm1);
        memberList.add(lm2);
        memberList.add(lm3);
        memberList.add(lm4);
        memberList.add(lm5);
        memberList.add(lm6);

From this array that I have put the information in I want the user to input a letter and for the program to output all the names and surnames containing that specific letter.

Answer 1

List.contains() only tells you if the list contains a certain object based on equals . And contains would expect an argument of the List type (in your case LibraryMembers ).

But you can achieve the desired result as follows. This presumes that you have getters and setters for first and last names. It works by streaming the memberlist and searching each name for the desired letter. The search is case significant but can be changed using toLowerCase on the names and always using lower case on the required character or substring to find.

boolean result = memberList.stream()
              .anyMatch(lm->lm.getLastName().contains("G") || 
                            lm.getFirstName().contains("G"));

Then do your test on result.

If you want to recover all the entries that match, you can do this.

List<LibraryMembers> results = memberList.stream()
     .filter(lm->lm.getLastName().contains("G") || 
             lm.getFirstName().contains("G"))
      .collect(Collectors.toList());

if (results.size() > 0) {
   results.forEach(System.out::println); // requires toString override
                                         // in LibraryMember class.
} else {
   System.out.println("Request not found");
}

Answer 2

I want the program to look something like this:

System.out.println("The program will allow the user to search for a string by typing a 
letter")

userAnswer = scan.next();

boolean userAnswer = memberList.contains("G"); 
    
        if (userAnswer)
            System.out.println("The list contains Glock,");
        else
            System.out.println("The list does not contain any words with that letter");
        

So that the information comes from:

import java.util.*;

public class Library {

    



public static void main (String[] args)
{
    
    
    ArrayList<Book> bookList = new ArrayList<Book>();
    ArrayList<libraryMembers> memberList = new ArrayList<libraryMembers>();
    
    
String userChoice;

{
  
    
    
    
    
    //Using previous class and assigning values to ID, Phone, Name, and Surname
    libraryMembers lm1 = new libraryMembers (1111, 3234231, "Glock", "John");
    libraryMembers lm2 = new libraryMembers (1112, 3234231, "Ackerman", "Mikasa");
    libraryMembers lm3 = new libraryMembers (1113, 341231, "Crab", "Armin");
    libraryMembers lm4 = new libraryMembers (1114, 3423431, "Bacony", "Conny");
    libraryMembers lm5 = new libraryMembers (1115, 3423431, "Jaeger", "Erwin");
    libraryMembers lm6 = new libraryMembers (1116, 3423431, "Jaeger", "Zeke");
    
    //Printing member information
    lm1.informationPrint();
    lm2.informationPrint();
    lm3.informationPrint();
    lm4.informationPrint();
    lm5.informationPrint();
    lm6.informationPrint();

// The line above just prints out the information

    memberList.add(lm1);
    memberList.add(lm2);
    memberList.add(lm3);
    memberList.add(lm4);
    memberList.add(lm5);
    memberList.add(lm6);
    
// Using this line I have added my lists to the array

It does not need to be case sensitive.

I've tried something like this:

public static void main (String[] args) {

    ArrayList<String> memberList = new ArrayList<String>();

memberList.add("Glock, John, Ackerman, Mikasa, Crab, Armin, Bacony, Conny, 
Jaeger, Erwin, Jaeger, Zeke");

boolean userAnswer = memberList.contains("G");
    
    if (userAnswer)
        System.out.println("The list contains Glock");
    else
        System.out.println("The list does not containg string with letter g");
        

But the only way I can find something is by typing out the full string not the letter.