StringBuilder In Java – Efficient String Handling

Welcome back, students! After our comprehensive dive into the world of Strings in Java, you now know that Strings are immutable. This immutability, while beneficial for reasons we’ve discussed, can lead to inefficiency when performing extensive String manipulations. This is where StringBuilder in Java steps into the scene. In today’s lesson, we will delve into this valuable class and understand its role in Java.

What Is StringBuilder In Java?

StringBuilder is a class in Java, introduced in Java 5, designed to store mutable sequence of characters. Unlike String objects, StringBuilder objects can be modified over time.

Let’s take a simple example of creating a StringBuilder:

StringBuilder builder = new StringBuilder();

Here, we have created an empty StringBuilder object. You can also initialize a StringBuilder with an initial String value:

StringBuilder builder = new StringBuilder("Hello");

Key Methods Of StringBuilder In Java

StringBuilder class comes with several handy methods for manipulating strings. Here are a few:

  • append(): This method adds the parameter to the end of the current StringBuilder.
StringBuilder builder = new StringBuilder("Hello");
builder.append(", world!");
System.out.println(builder); // Outputs "Hello, world!"
  • insert(int offset, String str): This method inserts the second parameter into the StringBuilder at the specified offset.
StringBuilder builder = new StringBuilder("Hello, world!");
builder.insert(7, "beautiful ");
System.out.println(builder); // Outputs "Hello, beautiful world!"
  • delete(int start, int end): This method deletes the substring from the start index to the end index from the current StringBuilder.
StringBuilder builder = new StringBuilder("Hello, beautiful world!");
builder.delete(7, 17);
System.out.println(builder); // Outputs "Hello, world!"
  • reverse(): This method reverses the current StringBuilder.
StringBuilder builder = new StringBuilder("Hello, world!");
System.out.println(builder); // Outputs "!dlrow ,olleH"

Why Should We Use StringBuilder?

The main reason we use StringBuilder is for efficiency when performing multiple string manipulations. Since String is immutable, every time you manipulate a String, a new String object is created, which can be very memory-inefficient.

StringBuilder, on the other hand, allows modifications to the same object, hence it’s faster and more memory-efficient.

Here is a simple illustration:

String str = "Hello";
str += ", ";
str += "world!";

In this code, three String objects are created.

Now let’s look at how we can do the same thing using StringBuilder:

StringBuilder builder = new StringBuilder("Hello");
builder.append(", ");

In this code, only one StringBuilder object is created, regardless of how many operations are performed.


The StringBuilder class is a powerful tool for handling and manipulating strings in Java. It can greatly improve the performance of your Java program when dealing with heavy string operations.

However, remember that StringBuilder is not synchronized, meaning it’s not thread-safe. If you require thread safety, consider using StringBuffer, which has the same functionality but is thread-safe.

In our next lesson, we will discuss the StringBuffer in java class and when to use StringBuffer over StringBuilder. Until then, keep practicing and happy coding!

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