What are the main differences between String, StringBuilder, and StringBuffer?

Question

Ravi Vishwakarma · Answer

String
String objects are immutable, meaning once an String object is created, it cannot be changed. Any modification results in the creation of a new
String object. String is inherently thread-safe because of its immutability.
Due to immutability, concatenating strings and String can be less efficient because it involves creating new objects and copying existing content. Used when the value of the string will not change or will change infrequently.
String str = "Hello";
str = str.concat(", World!"); // A new String object is created
StringBuilder
StringBuilder objects are mutable, meaning they can be modified after they are created without creating new objects.
StringBuilder is not thread-safe, which means it is not synchronized and should not be used in a multi-threaded environment.
StringBuilder sb = new StringBuilder("Hello");
sb.append(", World!"); // Modifies the existing object
Generally faster than StringBuffer because it does not have the overhead of synchronization. It is also more efficient than
String for concatenation operations due to mutability. Used when you need a mutable sequence of characters and are working in a single-threaded environment.
StringBuffer
StringBuffer objects are mutable, similar to StringBuilder.
StringBuffer is thread-safe because its methods are synchronized, which makes it safe to use in a multi-threaded environment.
Slower than StringBuilder due to the overhead of synchronization but still more efficient than
String for concatenation operations in a multi-threaded context. Used when you need a mutable sequence of characters in a multi-threaded environment.
StringBuffer sb = new StringBuffer("Hello");
sb.append(", World!"); // Modifies the existing object
Key Differences
Feature
String
StringBuilder
StringBuffer
Mutability
Immutable
Mutable
Mutable
Thread Safety
Thread-safe (inherently due to immutability)
Not thread-safe
Thread-safe (methods are synchronized)
Performance
Slower for concatenation due to immutability
Faster due to lack of synchronization
Slower than StringBuilder due to synchronization
Usage
When the string value does not change often
Single-threaded environment for mutable strings
Multi-threaded environment for mutable strings
Read moreand 
How do you implement a singleton pattern in Java?
What is the significance of the final keyword when applied to classes, methods, and variables?
and

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What are the main differences between String, StringBuilder, and StringBuffer?

Anubhav Kumar

1 Answers

String

StringBuilder

StringBuffer

Key Differences

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Feature	String	StringBuilder	StringBuffer
Mutability	Immutable	Mutable	Mutable
Thread Safety	Thread-safe (inherently due to immutability)	Not thread-safe	Thread-safe (methods are synchronized)
Performance	Slower for concatenation due to immutability	Faster due to lack of synchronization	Slower than `StringBuilder` due to synchronization
Usage	When the string value does not change often	Single-threaded environment for mutable strings	Multi-threaded environment for mutable strings