Convert String to List of Characters in Java

In this article, we will learn how to convert a string to a list of characters in Java. Sometimes, when we handle character-based data structures, we need to convert a string into a list of characters.

In Java, a string is a sequence of characters and is represented by the String class. A list is a collection of elements and is represented by the List interface.

Converting a String to a List of Characters

The following are the different approaches to convert a string to a list of characters in Java -

• Using String.toCharArray()
• Using String.toList()
• Using StringBuilder
• Using String.valueOf()
• Using Java Streams

Using String.toCharArray()

The String.toCharArray() method converts a string into an array of characters. This method returns a new character array containing the same characters as the string.

Example

Following are the steps to convert a string to a list of characters using String.toCharArray() -

• The String.toCharArray() method is called on the string to convert it into a character array.
  
• The Arrays.asList() method is used to convert the character array into a list.
  
• The List interface is used to store the characters.
• Finally, the list is printed.

Let's say the following is our string -

String str = "Welcome";

Convert the string to a list of characters -

List<Character> list = Arrays.asList(str.toCharArray());

Here, the Arrays.asList() method is used to convert the character array into a list of characters.

Example

Below is an example of converting a string to a list of characters using String.toCharArray() -

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

public class Demo {
   public static void main(String[] args) {
      String str = "Welcome";
      List list = new ArrayList<>();
      for (char ch : str.toCharArray()) {
         list.add(ch); // Autoboxing from char to Character
      }
      System.out.println("List of characters = " + list);
   }
}

Output

List of characters = [W, e, l, c, o, m, e]

Time Complexity: O(N), each character is processed once. Space Complexity: O(N), creates a new character array and list object.

Using String.toList()

The String.toList() method converts a string into a list of characters. This method returns a new list containing the same characters as the string. Following are the steps to convert a string to a list of characters using String.toList() -

• The String.toList() method is called on the string to convert it into a list of characters.
• The List interface is used to store the characters.
• Finally, the list is printed.

Let's say the following is our string -

String str = "Welcome";

Convert the string to a list of characters -

List<Character> list = str.toList();

Here, the String.toList() method is used to convert the string into a list of characters.

Example

Below is an example of converting a string to a list of characters using String.toList() -

import java.util.List;
import java.util.ArrayList;
public class Demo {
   public static void main(String[] args) {
      String str = "Welcome";
      List<Character> list = new ArrayList<>();
      for (char c : str.toCharArray()) {
         list.add(c);
      }
      System.out.println("List of characters = "+list);
   }
}

Output

List of characters = [W, e, l, c, o, m, e]

Time Complexity: O(N), each character is processed once. Space Complexity: O(N), creates a new character array and list object.

Using StringBuilder

The StringBuilder class offers a more efficient way to convert a string to a list of characters. This method is faster than the String.toCharArray() method. Following are the steps to convert a string to a list of characters using StringBuilder -

• A StringBuilder object is initialized.
• A for-each loop iterates over the string, appending each character.
• The List interface is used to store the characters.
• Finally, the list is printed.

A StringBuilder object sb, is created using the StringBuilder class -

StringBuilder sb = new StringBuilder();

Convert the StringBuilder object into a list of characters -

List<Character> list = new ArrayList<>();

Here, the ArrayList class is used to create a list of characters. Convert the StringBuilder object into a list of characters -

for (char c : sb.toString().toCharArray()) {
   list.add(c);
}

Here, the ArrayList class is used to create a list of characters.

Example

Below is an example of converting a string to a list of characters using StringBuilder -

import java.util.List;
import java.util.ArrayList;
import java.lang.StringBuilder;
public class Demo {
   public static void main(String[] args) {
      String str = "Welcome";
      StringBuilder sb = new StringBuilder(str);
      List<Character> list = new ArrayList<>();
      for (char c : sb.toString().toCharArray()) {
         list.add(c);
      }
      System.out.println("List of characters = "+list);
   }
}

Output

List of characters = [W, e, l, c, o, m, e]

Time Complexity: O(N), each character is processed once. Space Complexity: O(N), creates a new character array and list object.

Using String.valueOf()

The String.valueOf() method converts a character to a string. This method returns a new string containing the same characters as the original string. Following are the steps to convert a string to a list of characters using String.valueOf() -

• The String.valueOf() method is called on the string to convert it into a character.
• The List interface is used to store the characters.
• Finally, the list is printed.

Example

Below is an example of converting a string to a list of characters using String.valueOf() -

import java.util.List;
import java.util.ArrayList;
import java.lang.String;
public class Demo {
   public static void main(String[] args) {
      String str = "Welcome";
      List list = new ArrayList<>();
      for (char c : str.toCharArray()) {
         list.add(c); // Correct: adding the actual character
      }
      System.out.println("List of characters = "+list);
   }
}

Output

List of characters = [W, e, l, c, o, m, e]

Time Complexity: O(N), each character is processed once. Space Complexity: O(N), creates a new character array and list object.

Using Java Streams

Java Streams provide a functional way to process collections. The map() function is used to convert each character into a string, Collectors.joining() is used to concatenate them. Following are the steps to convert a string to a list of characters using Java streams ?

• stream() to convert the string into a stream.
• map(String::valueOf) converts each character to a string.
• collect(Collectors.toList()) collects all string elements into a list.
• Finally, the list is printed.

Example

Below is an example of converting a string to a list of characters using Java streams -

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.lang.String;
public class Demo {
   public static void main(String[] args) {
      String str = "Welcome";
      List<Character> list = str.chars().mapToObj(c -> (char)c).collect(Collectors.toList());
      System.out.println("List of characters = "+list);
   }
}

Output

List of characters = [W, e, l, c, o, m, e]

Time Complexity: O(N), each character is processed once. Space Complexity: O(N), creates a new character array and list object.