Comparison - String, StringBuilder & StringBuffer

Difference between String, String Builder, and String Buffer

Feature	String	StringBuilder	StringBuffer
Mutability	Immutable	Mutable	Mutable
Thread Safety	Thread-safe (because it's immutable)	Not thread-safe	Thread-safe
Storage	String variables are stored in a “constant string pool”	String values are stored in a stack. If the values are changed then the new value replaces the older value.	Same as StringBuilder
Performance	Slower in operations involving multiple string modifications	Faster for single-threaded operations involving multiple string modifications	Slower than StringBuilder due to synchronization overhead
Usage	Used when the string value will not change or change infrequently	Used when the string value will change frequently and thread safety is not a concern	Used when the string value will change frequently and thread safety is a concern
Methods Available	Limited to standard string operations (e.g., length, charAt, substring)	Extensive methods for modifying strings (e.g., append, insert, delete, reverse)	Similar to StringBuilder with synchronized methods for thread safety
Thread Synchronization	Not applicable	Not synchronized	Synchronized methods
Memory Allocation	Fixed and cannot be changed after creation	Can grow dynamically	Can grow dynamically
String Pool	Supports string pool	Does not support string pool	Does not support string pool
Performance in Concatenation	Poor performance in concatenation (each concatenation creates a new object)	Better performance for concatenation (modifies the existing object)	Better performance for concatenation (modifies the existing object, but slower than StringBuilder)
Example Initialization	String str = "Hello";	StringBuilder sb = new StringBuilder("Hello");	StringBuffer sb = new StringBuffer("Hello");
Usage Scenario	Best for read-only or rarely modified strings	Best for frequently modified strings in single-threaded contexts	Best for frequently modified strings in multi-threaded contexts
Example Operations	str.concat(" World");	sb.append(" World");	sb.append(" World");

// String
String str = "Hello";
str = str.concat(" World"); // Creates a new string "Hello World"
System.out.println(str);    // Output: Hello World

// StringBuilder
StringBuilder sb = new StringBuilder("Hello");
sb.append(" World"); // Modifies the existing StringBuilder object
System.out.println(sb.toString()); // Output: Hello World

// StringBuffer
StringBuffer sb = new StringBuffer("Hello");
sb.append(" World"); // Modifies the existing StringBuffer object
System.out.println(sb.toString()); // Output: Hello World