在 java 中从字符串转换为 arrayList 的问题

Question

I've got a problem, I'm trying to convert a String to an ArrayList but it does'nt work: it says in the console that Type mismatch: cannot convert from list to ArrayList my little program :

package nfa032.application;
import java.util.*;
import java.util.ArrayList;
import java.util.Scanner;
import java.io.*;
public class ArrayListUtils {

public static void AfficherArrayListString(ArrayList<String>a) 
{
    for(int i=1; i<=a.size(); i++)
    { 
    System.out.println(a.get(i));
    }
}

public static ArrayList<String> lireArrayListString(int n) throws IOException
{
    InputStreamReader isr=new InputStreamReader(System.in);
    BufferedReader in=new BufferedReader(isr);
    String s;
    String [] str;
    ArrayList liste=new ArrayList<String>();
    for(int i=1; i<=n; i++)

    {
        System.out.println("Entrer une chaîne.");
        s=in.readLine();
        str=s.split("\\s+");
        liste=Arrays.asList(str);       
     }
     return liste;
}

}

Answer 1

I guess the problem is this line liste=Arrays.asList(str);

It's because you are trying to assign an interface List to an implementation of that interface which is ArrayList

To solve this you can do List<String> liste=new ArrayList<String>();

Answer 2

There are several problems with the code you have.

• Your liste variable doesn't have a diamond operator specified ArrayList should be ArrayList<String> to indicate that it will contain String elements (for more info on diamond operators https://www.baeldung.com/java-diamond-operator )

• Arrays.asList() does not return an ArrayList<> , but it returns a List<> (The super type of ArrayList). If you want to use Arrays.asList , you need to change the type of liste to List<String>

Code becomes something like this

public static void AfficherArrayListString(final ArrayList<String> a) {
    for (int i = 1; i <= a.size(); i++) {
        System.out.println(a.get(i));
    }
}

public static List<String> lireArrayListString(final int n) throws IOException {
    final InputStreamReader isr = new InputStreamReader(System.in);
    final BufferedReader in = new BufferedReader(isr);
    String s;
    String[] str;
    List<String> liste = new ArrayList<>();
    for (int i = 1; i <= n; i++) {
        System.out.println("Entrer une chaîne.");
        s = in.readLine();
        str = s.split("\\s+");
        liste = Arrays.asList(str);
    }
    return liste;
}

Answer 3

public static ArrayList<String> lireArrayListString(int n) throws IOException
{
    InputStreamReader isr=new InputStreamReader(System.in);
    BufferedReader in=new BufferedReader(isr);
    String s;
    String [] str;
    ArrayList<String> liste=new ArrayList<String>();
    for(int i=1; i<=n; i++)
    {
        System.out.println("Entrer une chaîne.");
        s=in.readLine();
        str=s.split("\\s+");
        liste=(ArrayList<String>) Arrays.asList(str);
        
    }
    return liste;
}

}