Why String is immutable in Java?

In Java, a String object is immutable, meaning that its value cannot be changed once it is created. This design decision was made for several reasons, including:

1. Security: Because String objects are used extensively in Java for holding sensitive data such as passwords and cryptographic keys, making them immutable helps to prevent the value of the string from being modified by an attacker who may try to modify it in memory or over a network.

2. Thread-safety: Because immutable objects are thread-safe, meaning that they can be accessed and modified by multiple threads simultaneously without causing race conditions, using immutable String objects helps to ensure that multiple threads can safely access and use the same object.

3. Efficiency: Because String objects are immutable, Java can optimize string manipulation operations such as concatenation and substring operations by reusing existing String objects rather than creating new ones, which can save memory and improve performance.

4. Simplicity: By making String objects immutable, Java eliminates the need for developers to worry about the state of the object, which can simplify programming and reduce the likelihood of programming errors.

In summary, the immutability of String objects in Java helps to improve security, thread-safety, efficiency, and simplicity, making it a valuable design decision for the Java language.

References

1. https://docs.oracle.com/javacard/3.0.5/api/javacardx/annotations/StringPool.html
2. https://docs.oracle.com/javase/tutorial/essential/concurrency/immutable.html