Convert List of Characters to String in Java

Given a list of characters. In this article, we will write a Java program to convert the given list to a string.

Example of List-to-String Conversion

Input : list = {'g', 'e', 'e', 'k', 's'} 
Output : "geeks"

Input : list = {'a', 'b', 'c'} 
Output : "abc" 

Strings – Strings in Java are objects that are supported internally by a char array. Since arrays are immutable, and strings are also a type of exceptional array that holds characters, therefore, strings are immutable as well. 

List – List in Java implements the ability to manage the ordered collection. It comprises index-based techniques to insert, update, delete, and search the elements of the list. It can have duplicate elements also. The List interface is located in java.util package and inherits the Collection interface.

Methods to Convert List to String in Java

There are numerous approaches to convert the List of Characters to String in Java. These are – 

• Using StringBuilder class
• Using join() method of Joiner class
• Using List.toString(), String.substring() and String.replaceAll() method
• Using Collectors

1. Using StringBuilder class to Convert List to String

A simple solution would be to iterate through the list and create a new string with the help of the StringBuilder class, as shown below:

Java

// Java program for convert character list to string
import java.util.Arrays;
import java.util.List;

// Convert List of Characters to String in Java
class GFG {
    public static void main(String[] args)
    {
        // create character list and initialize
        List<Character> str
            = Arrays.asList('G', 'e', 'e', 'k', 's');

        System.out.println("List - " + str);

        // create object of StringBuilder class
        StringBuilder sb = new StringBuilder();

        // Appends characters one by one
        for (Character ch : str) {
            sb.append(ch);
        }

        // convert in string
        String string = sb.toString();

        // print string
        System.out.println("String - " + string);
    }
}

Output

List - [G, e, e, k, s]
String - Geeks

The complexity of the above method

Time Complexity: O(n)
Auxiliary Space: O(n)

2. Using join() method of Joiner Class  

A joiner class can be used to join pieces to text specified as an array and return the results as a string. This method is also called the Guava method.

Below is the implementation of the above method: 

Java

// Java program for convert character list to string
import com.google.common.base.Joiner;
import java.util.*;

// Convert List of Characters to String in Java
class GFG {
    public static void main(String[] args)
    {
        // create character list and initialize
        List<Character> str
            = Arrays.asList('G', 'e', 'e', 'k');

        System.out.println("List - " + str);

        // convert in string
        // use join() method
        String string = Joiner.on("").join(str);

        // print string
        System.out.println("String - " + string);
    }
}

Output

List - [G, e, e, k]
String - Geek

The complexity of the above method

Time Complexity: O(n)
Auxiliary Space: O(n)

3. Using List.toString(), String.substring() and String.replaceAll() method

The toString() method on a list returns a string that is surrounded by square brackets and has commas between items. The idea is to get rid of square brackets using the substring() method and comma and space replace using the replaceAll() method.

The Below implementation of the above method is given below:

Java

// Java program for convert character list to string
import java.util.*;

// Convert List of Characters to String in Java
class GFG {
    public static void main(String[] args)
    {
        // create character list and initialize
        List<Character> str
            = Arrays.asList('G', 'e', 'e', 'k');

        System.out.println("List - " + str);

        // convert in string
        // remove [] and spaces
        String string
            = str.toString()
                  .substring(1, 3 * str.size() - 1)
                  .replaceAll(", ", "");

        // print string
        System.out.println("String - " + string);
    }
}

Output

List - [G, e, e, k]
String - Geek

The complexity of the above method:

Time Complexity: O(n)
Auxiliary Space: O(n)

4. Using Collectors in Java for List-to-String Conversion

In Java 8, we can make use of stream API with Java collectors.

Below is the implementation of the above method:

Java

// Java program for convert character list to string
import java.util.*;
import java.util.stream.Collectors;

// Convert List of Characters to String in Java
class GFG {
    public static void main(String[] args)
    {
        // create character list and initialize
        List<Character> str
            = Arrays.asList('G', 'e', 'e', 'k');

        System.out.println("List - " + str);

        // convert in string
        // using collect and joining() method
        String string = str.stream()
                            .map(String::valueOf)
                            .collect(Collectors.joining());

        // print string
        System.out.println("String - " + string);
    }
}

Output

List - [G, e, e, k]
String - Geek

The complexity of the above method:

Time Complexity: O(n)
Auxiliary Space: O(n)