Java StringBuilder

The StringBuilder class bears an uncanny resemblance to its counterpart, StringBuffer, with the exception of a crucial distinction. It is imperative to note that the former, unlike the latter, lacks the synchronization feature, rendering it unsuitable for thread safety. This disparity between StringBuffer and StringBuilder can be encapsulated by the fact that StringBuffer possesses synchronization capabilities, while StringBuilder does not.

Therefore, it is highly recommended to utilize StringBuilder in every conceivable scenario where your object is accessed solely by a solitary thread. By adhering to this practice, you ensure the optimal functioning and integrity of your program.

The important methods in StringBuilder Class are append() , insert() , replace() , delete() , reverse() , and capacity() . The following Java program illustrate the important methods in StringBuilder Class.

class TestClass{ public static void main (String[] args){ //adding values in StringBuilder StringBuilder sb = new StringBuilder("The "); sb.append( "Java " ); sb.append( "Tutorial " ); System.out.println(sb); //output: The Java Tutorial //insert the specified string with this string at the specified position sb.insert(8," StringBuilder "); System.out.println(sb); //output: The Java StringBuilder Tutorial //replace the string from specified startIndex and endIndex sb.replace(4,4,"Good"); System.out.println(sb); //output: The GoodJava StringBuilder Tutorial //delete the string from specified startIndex and endIndex sb.delete(0,4); System.out.println(sb); //output: GoodJava StringBuilder Tutorial //reverse the string sb.reverse(); System.out.println(sb); //output: lairotuT redliuBgnirtS avaJdooG //return the current capacity StringBuilder nsb = new StringBuilder(); System.out.println(nsb.capacity()); //output: 16 , the default capacity 16 nsb.append("The Java Tutorial "); System.out.println(nsb.capacity()); //output: 34 , (oldcapacity*2)+2 , (16*2)+2 } }
The Java Tutorial The Java StringBuilder Tutorial The GoodJava StringBuilder Tutorial GoodJava StringBuilder Tutorial lairotuT redliuBgnirtS avaJdooG 16 34 34 34

StringBuilder append() method

The primary operations performed on a StringBuilder revolve around its append method, which is designed to accommodate data of any type. It is worth highlighting that the append method is ingeniously overloaded, allowing for a versatile and seamless integration of various data types.

However, it is essential to recognize that the cost of appending strings escalates as the length of the strings grows, ultimately demanding more memory resources. Consequently, it becomes increasingly crucial to be mindful of the potential memory overhead associated with string appends, particularly when dealing with lengthy strings. By understanding this aspect, developers can make informed decisions regarding memory management and optimize the efficiency of their code. For example:

class TestClass{ public static void main (String[] args) { String str = ""; for (int i = 0; i < 100; i++) { str += ", " + i; } System.out.println(str); } }

In the above case, you should use a StringBuilder instead of a String, because it is much faster and consumes less memory.

class TestClass{ public static void main (String[] args) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < 100; i++) { sb.append(i + ", " ); } System.out.println(sb); } }

If you have a single statement,

String s = "a, " + "b, " + "c, " + "d, " ...;

then you can use Strings, because the compiler will use StringBuilder automatically.

Mutability Difference of String and StringBuilder

One notable distinction between String and StringBuilder lies in their mutability characteristics. Strings are immutable, meaning that when an attempt is made to alter their values, a new object is created to store the modified string. On the other hand, StringBuilder objects are mutable, enabling them to modify and change their values without the need for creating new objects.

The immutability of Strings has implications for memory usage and performance. Whenever a modification is made to a String, a new object must be created in memory, which can result in increased memory consumption, especially when dealing with frequent modifications or concatenations of strings. This immutability is beneficial in terms of thread safety and guarantees that the content of a String remains unchanged once created, preventing unintended modifications.

In contrast, the mutability of StringBuilder provides a more efficient approach when it comes to modifying strings. StringBuilder objects can be updated and modified directly, without the need for creating new objects, thus reducing memory overhead and enhancing performance, particularly in scenarios where extensive string manipulations are required.


Understanding the mutability difference between String and StringBuilder is crucial in choosing the appropriate data type for specific scenarios, considering factors such as memory efficiency, performance optimization, and the need for thread safety.