Convert List to String in Java

Sometimes, we need to convert a list of characters into a string. A string is a sequence of characters, so we can easily form a string from a character array. We have some special strings, such as a palindrome string (a string that is the same as the original string after reversing it). In order to reverse a string, we need to convert the string into a char array for reversing all the chars of string, and after reversing the char array, we need to convert it into a string.

In Java, we have several ways through which we can convert a list into a string are as follows:

1. Using StringBuilder class

We have a very simple way to convert a list into a string, i.e., by using the StringBuilder class. We iterate the list of char using for loop and generate a new string with the help of StringBuilder.

Let's implement the code for converting a list into a string by using the StringBuilder class:

ConvertListToStringExample1.java

// import required classes and packages if any
package javaTpoint.JavaExample;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

// create class ConvertListToStringExample1 that will convert user given char list into a string
class ConvertListToStringExample1 {
	// main() method start
	public static void main(String[] args)
	{
		// declare variables and list
		int size;
		String str;
		List<Character> charList = new ArrayList<Character>();
		
		// create Scanner class object to take input from user
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter size of char list.");
		size = sc.nextInt();
		
		for(int i = 0; i < size; i++) {
			System.out.println("Enter char["+i+"]: ");
			charList.add(sc.next().charAt(0));
		}
		
		// close Scanner class object
		sc.close();
		
		// display chrList elements
		System.out.println("List: " + charList);

		// create an object of StringBuilder class
		StringBuilder builder = new StringBuilder();

		// iterate charList and append each char to builder one by one
		for (Character ch : charList) {
			builder.append(ch);
		}

		// convert StringBuilder object into string
		str = builder.toString();

		// display string
		System.out.println("String after converting list: " + str);
	}
}

Output:

2. Using Joiner class

Like StringBuilder, we have one more class, i.e., Joiner class, through which we can convert a list into a string. We use the join() method of the Joiner class, which is also known as the Guava method. The join() method joins the pieces into the specified text as an array and returns the results as a string.

Let's implement the code for converting a list into a string by using the Joiner class:

We are using the maven project, so it is required to add the following dependency in our POM.xml file.

<dependency>
	<groupId>com.google.guava</groupId>
  	<artifactId>guava</artifactId>
  	<version>r05</version>
</dependency>

ConvertListToStringExample2.java

// import required classes and packages if any

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import com.google.common.base.Joiner;

// create class ConvertListToStringExample2 that will convert user given char list into a string using Joiner class
class ConvertListToStringExample2 {
	// main() method start
	public static void main(String[] args)
	{
		// declare variables and list
		int size;
		String str;
		List<Character> charList = new ArrayList<Character>();
		
		// create Scanner class object to take input from user
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter size of char list.");
		size = sc.nextInt();
		
		for(int i = 0; i < size; i++) {
			System.out.println("Enter char["+i+"]: ");
			charList.add(sc.next().charAt(0));
		}
		
		// close Scanner class object
		sc.close();
		
		// display chrList elements
		System.out.println("List: " + charList);


		// convert list into string by using Joiner class
		str = Joiner.on("").join(charList);

		// display string
		System.out.println("String after converting list: " + str);
	}
}

Output:

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

In this way of converting a list into a string, we use three methods of List and String classes. We use three methods to perform the following operations:

We use the toString() method of the list to convert the list into a string. The return string will also contain opening/closing square brackets and commas.
We use the substring() method to get rid of opening/closing square brackets.
We use the replaceAll() method to replace all the commas and spaces with blank or null.

Let's implement the code for converting a list into a string by using the toString(), substring(), and replaceAll() methods:

ConvertListToStringExample3.java

// import required classes and packages if any
package javaTpoint.JavaExample;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

// create class ConvertListToStringExample2 that will convert user given char list into a string using toString(), substring() and replaceAll() methods
class ConvertListToStringExample3 {
	// main() method start
	public static void main(String[] args)
	{
		// declare variables and list
		int size;
		String str;
		List<Character> charList = new ArrayList<Character>();
		
		// create Scanner class object to take input from user
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter size of char list.");
		size = sc.nextInt();
		
		for(int i = 0; i < size; i++) {
			System.out.println("Enter char["+i+"]: ");
			charList.add(sc.next().charAt(0));
		}
		
		// close Scanner class object
		sc.close();
		
		// display chrList elements
		System.out.println("List: " + charList);


		// convert list into string by using all the three methods of String and List class
		str = charList.toString()
				.substring(1, 3 * charList.size() - 1)
				.replaceAll(", ", "");

		// display string
		System.out.println("String after converting list: " + str);
	}
}

Output:

4. Using Collectors in Java

It is the last way to convert a list into a string. We use it rarely because here, we use stream API with collectors, which is available only in Java8.

Let's implement the code for converting a list into string by using the stream API with Collectors.

ConvertListToStringExample3.java

// import required classes and packages if any
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;

// create class ConvertListToStringExample4 that will convert user given char list into a string using Collectors
class ConvertListToStringExample4 {
	// main() method start
	public static void main(String[] args)
	{
		// declare variables and list
		int size;
		String str;
		List<Character> charList = new ArrayList<Character>();
		
		// create Scanner class object to take input from user
		Scanner sc = new Scanner(System.in);
		
		System.out.println("Enter size of char list.");
		size = sc.nextInt();
		
		for(int i = 0; i < size; i++) {
			System.out.println("Enter char["+i+"]: ");
			charList.add(sc.next().charAt(0));
		}
		
		// close Scanner class object
		sc.close();
		
		// display chrList elements
		System.out.println("List: " + charList);


		// convert list into string by using collect() and joining() methods
		str = charList.stream()
				.map(String::valueOf)
                .collect(Collectors.joining());

		// display string
		System.out.println("String after converting list: " + str);
	}
}

Output: