Java Tutorial



Java Tutorial

StringBuilder Class in java


String manipulation is a common task in many Java programs. In comparison to the immutable String class, the StringBuilder class offers flexibility and better efficiency when working with mutable strings. The StringBuilder in Java is an essential resource when you need to concatenate, insert, delete, or alter strings dynamically.

StringBuilder instances are mutable, unlike the String class, which creates a new object whenever a change is performed. This enables direct modification of them without the creation of new objects, leading to quicker and more effective string manipulation procedures. The StringBuilder class accomplishes this by using an internal dynamic array, which enables it to modify its size as necessary and prevents irrational memory allocations.

This post will examine the numerous facets of the Java StringBuilder class, including how to take input in StringBuilder in Java. Our first step is to understand its class declaration, syntax, and internal operations. Then, using real-world examples, we'll go into the constructors and methods offered by the StringBuilder class. With this write-up, you will thoroughly understand how to use the StringBuilder class to your advantage for string manipulation requirements.

So let's go out on a quest to discover the strength and adaptability of Java's StringBuilder class. Regardless of your level of programming experience, this article will arm you with the knowledge and examples you need to make the most of StringBuilder's features and improve your ability to manipulate StringBuilder Java 8.


The StringBuilder in Java provides a flexible and efficient way to manipulate strings. Unlike the immutable String class, StringBuilder objects are mutable, allowing for efficient modification without creating new objects. This article explores the class declaration, syntax, internal working, constructors, methods, and practical examples of StringBuilder in Java, empowering you with the knowledge to manipulate strings in programming efficiently.

Class Declaration of StringBuilder

The StringBuilder class in Java is declared as follows:

public final class StringBuilder extends Object implements Serializable, CharSequence

The class is declared as `public` and `final`, meaning it can be accessed from anywhere in the code but cannot be subclassed. StringBuilder extends the Object class and implements the Serializable and CharSequence interfaces, providing additional functionality and ensuring compatibility with other Java APIs.

Syntax of StringBuilder in Java

To create an instance of StringBuilder, use the following syntax:

This creates a new StringBuilder object with an initial capacity of 16 characters. The capacity can increase dynamically as needed.

Internal Working of StringBuilder in Java

Internally, StringBuilder stores a string of characters in a dynamic array. When more characters are added, it immediately increases its initial capacity. By dynamically resizing, needless memory allocations are avoided, and effective memory consumption is guaranteed.

StringBuilder modifies the internal array's size when executing string alteration operations like adding or inserting characters. It performs better than using the String class for frequent string updates because it avoids creating new objects and copies the old content when it can.

Looking at the Constructors of StringBuilder in Java w3schools

StringBuilder provides several constructors to create objects with different initial capacities or based on existing strings. Let's explore these constructors:

1. StringBuilder(): Creates an empty StringBuilder object with an initial capacity of 16 characters.

It initializes an empty StringBuilder with a starting size of 16 characters when you build a StringBuilder object using the default constructor 'StringBuilder().' The capacity shows how many characters a StringBuilder can store before having to resize its internal character array.

The StringBuilder can carry more characters than its initial 16-character limit, though. This merely indicates that the internal character array has a capacity of 16, enabling the StringBuilder to effectively handle a specific number of characters without scaling.

The StringBuilder will automatically resize its internal array to accommodate the extra characters if you append more than 16 characters to it and it exceeds its existing limit. The characters are resized by making a new, larger array and pasting the current array's characters into it.

StringBuilder strikes a compromise between memory efficiency and performance by starting with an initial capacity of 16. It keeps the flexibility to handle longer strings while avoiding frequent resizing for tiny string operations.

Here's an example to illustrate the use of the default constructor:

Output: 16

In this example, we create a new StringBuilder object using the default constructor and retrieve its capacity using the `capacity()` method. Since we haven't appended any characters yet, the initial capacity of 16 is returned.

2. StringBuilder(int capacity): Creates an empty StringBuilder object with the specified initial capacity.

3. StringBuilder(CharSequence seq): Creates a StringBuilder object with the same content as the specified CharSequence.

4. StringBuilder(String str): Creates a StringBuilder object with the same content as the specified string.

Let's explore some practical examples of using the methods provided by the StringBuilder class:

Methods in Java StringBuilder

StringBuilder provides various methods to manipulate strings efficiently. Let's discuss some relevant examples using the methods of StringBuilder in Java:

1. append(): This method is used to concatenate (append) characters or strings to the StringBuilder object.

Example 1: Applying the append() Method of StringBuilder in Java

Output: "Hello World"

2. capacity(): This method returns the current capacity of the StringBuilder object.

Example 2: Inserting String With the Insert() Method

Output: "Hello World"

3. charAt(): This method returns the character at the specified index within the StringBuilder object.

Example 3: Using the Replace() Method of StringBuilder in Java

Output: "Hello Java"

4. reverse(): This method reverses the sequence of characters within the StringBuilder object.

Example 4: Deleting a Substring From the Original String

Output: "Hello"

5. length(): This method returns the number of characters in the StringBuilder object.

Example 5: Applying the Reverse() Method of StringBuilder in Java

Output: "olleH"

6. indexOf(): This method returns the index within the StringBuilder object of the first occurrence of the specified substring.

Example 6: Looking at the Capacity() Method

Output: 21

7. lastIndexof(): This method returns the index within the StringBuilder object of the last occurrence of the specified substring.

Example 7: Ensure Minimum Capacity With the Ensurecapacity() Method

Output: 30

8. isEmpty(): This method checks whether the StringBuilder object is empty or not.

Example 8: Using the Length() Method of Stringbuilder in Java

Output: 5

9. substring(): This method returns a new StringBuilder object that contains a subsequence of characters from the original StringBuilder object.

Example 9: Looking at the Charat() Method

Output: 'e'

Example 10: The Index of() Method of StringBuilder in Java

Output: 6

Calling StringBuilder Methods

To call the methods of the StringBuilder class, create an instance of StringBuilder and use the dot notation to access the desired method.

StringBuilder Length and Capacity

The length of a StringBuilder object refers to the number of characters it currently holds. It can be obtained using the `length()` method.

The capacity of a StringBuilder object refers to the total number of characters it can hold without resizing. You can obtain the capacity using the `capacity()` method.

Performing StringBuilder Operations

StringBuilder provides various methods for performing operations such as appending, inserting, replacing, deleting, and reversing strings. These operations can be executed on a StringBuilder object to modify its content efficiently.

The following example will help you understand the concept:


Output: "!dlroW olleH"

In this example, we start with a StringBuilder object initialized with the string "Hello." We then use the `append()` method to concatenate " World!" to the existing string, modifying the StringBuilder object directly. Next, we apply the `reverse()` method to reverse the sequence of characters within the StringBuilder object. Finally, we convert the StringBuilder object to a regular String using the `toString()` method and print the result.

By utilizing the append() and reverse() methods provided by StringBuilder, we can efficiently manipulate the string without creating new objects. This results in improved performance and memory efficiency.

Searching The Text in a StringBuilder Object

To search for a specific text within a StringBuilder object, you can use the `indexOf()` method to find the index of the first occurrence or the `lastIndexOf()` method to find the index of the last occurrence.

Converting The StringBuilder Object to a String

If you need to convert a StringBuilder object back to a regular String, you can use the `toString()` method. This method returns a string representation of the StringBuilder object.


In conclusion, the Java StringBuilder class is an effective tool for generating and modifying mutable character sequences. When doing string concatenation or modification operations, it performs faster and uses less memory than the String class, among other benefits. StringBuilder offers a flexible and effective approach for working with strings in Java thanks to its dynamic scaling features and different methods for adding, inserting, replacing, removing, and reversing strings.

The efficiency of your code will be enhanced by using the StringBuilder class, especially in situations where string manipulation occurs often or when a lot of data is involved. Additionally, it enables you to link together different operations, offering a simple way to construct and change strings.

Overall, you may significantly improve your string manipulation capabilities by learning how to take input in StringBuilder in Java and by utilizing the features and methods made available by the StringBuilder class.

By mastering StringBuilder in Java, you can use it across multiple languages. So for interested students or experts, the road is clear to explore StringBuilder in Java in Hindi.


1. What are the key distinctions between Java's String and the StringBuilder class?

Objects of type String cannot be changed in any way, while objects of type StringBuilder can be altered. The use of StringBuilder eliminates the requirement for creating new objects just so that strings can be modified.

2. What is the advantage of using StringBuilder rather than String while programming in Java?

 When dynamic string manipulation, such as concatenation or alteration, is necessary, use the StringBuilder. When string operations are performed frequently, it is especially helpful since it helps eliminate the performance overhead that comes with those operations.

3. Which one should I use, StringBuilder or StringBuffer, in a context that involves several threads?

Unfortunately, thread safety is not supported by StringBuilder. When working in a setting that supports many threads, if you are confused between StringBuilder and StringBuffer in Java, choose the latter. This is because StringBuffer in Java offers functionally comparable thread-safe functions.

4. How to transform a Java StringBuilder object into a regular String?

To convert a StringBuilder object to a String, use the 'toString()' method. This can be done successfully.

Leave a Reply

Your email address will not be published. Required fields are marked *