Can you tell me about the String class and its main features?

The String class in Java represents an immutable sequence of characters. Main features:

• Immutability: once a String object is created, it cannot be changed. Any operation that modifies the string creates a new object.
• Storage: strings are stored as an array of char characters.
• Optimization: strings use a string pool to save memory — identical literals refer to the same object.
• Methods: provides many methods for string manipulation, such as length(), substring(), indexOf(), equals(), toLowerCase(), etc.

Example:

String s1 = "hello";
String s2 = s1.toUpperCase(); // s2 = "HELLO", s1 remains "hello"