Immutable String

An immutable string in Java is a string object whose state cannot be modified once it has been created.

The String class in Java is an example of an immutable class. When you modify a string, for example, by concatenating two strings, a new string object is created, and the original string remains unchanged.

This makes strings thread-safe and suitable for use as a key in a HashMap or as a parameter to a method.

Why String in java immutable?

String is designed to be immutable in Java for several reasons:

  1. Security: Immutable strings are more secure because their values can't be changed by other parts of the code. This helps prevent security vulnerabilities and makes it easier to write safe, secure code.

  2. Concurrency: Because immutability ensures that a string's value cannot be changed, it makes it easier to write concurrent programs. Multiple threads can safely access the same string without having to worry about synchronization or data corruption.

  3. Efficiency: Strings are frequently used in hash tables, such as HashMap, and as keys in a map. When the string is used as a key, it must maintain its identity and hash code, so that it can be found and retrieved efficiently. This can be done more efficiently with an immutable string.

  4. Functionality: Immutable strings provide certain functionalities, such as interning, that are not possible with mutable strings. Interning allows multiple references to the same string to share the same memory, improving memory usage and performance.

In summary, immutability provides a high degree of stability, security, and efficiency to the Java String class, making it a preferred choice for many applications.

Why String class is Final in Java?

The String class in Java is declared as final because it is meant to be a final and complete implementation of an immutable string.

Declaring the String class as final prevents any subclass from modifying its behavior or state in an unintended way.

This helps ensure that the behavior and state of strings remain consistent and predictable, making it easier to write reliable code.

Additionally, declaring the String class as final allows the Java Virtual Machine (JVM) to optimize the implementation of strings.

For example, the JVM can cache frequently used strings, because it knows that their values will never change. This provides a significant performance improvement for frequently used strings.

In summary, the final keyword ensures that the String class is a stable and predictable implementation of an immutable string, providing benefits in terms of security, reliability, and performance.