What does it mean that the String class is immutable and why is it important?

The String class in Java is immutable, which means that once a String object is created, its contents cannot be changed. Any operations that seem to modify the string actually create a new String object.

This is important for several reasons:

• Security: Immutable objects are easier to use in multithreaded environments without synchronization.
• Caching: Strings can be safely cached and reused (for example, string pools).
• Predictable behavior: No side effects when working with strings.

Example:

String s = "hello";
s = s + " world"; // a new String object is created, the original "hello" remains unchanged