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 TutorAspire .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 charList = new ArrayList();    // 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:

Convert List to String in Java

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 charList = new ArrayList();    // 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:

Convert List to String in Java

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 TutorAspire .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 charList = new ArrayList();    // 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:

Convert List to String in Java

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 charList = new ArrayList();    // 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:

Convert List to String in Java

In all the above-discussed ways, we have frequently used the StringBuilder class for converting a list into a string.

Next TopicList of Constants in Java

Convert List to String in Java

Convert List to String in Java

1. Using StringBuilder class

2. Using Joiner class

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

4. Using Collectors in Java

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