Java String Characteristics Explained

In Java, java.lang.String is an immutable class, which means that once a String object is created, its contents cannot be changed. This feature is mainly due to the existence of the string constant pool, adopted for performance and security reasons.

Furthermore, the String class also has the following characteristics:

1. Immutability: Once a String object is created, its content cannot be changed. Any operation on a String object will return a new String object, and the original object will not be affected.
2. Thread safety: Because strings are immutable, multiple threads can operate on the same string object simultaneously without causing any thread safety issues.
3. Caching hash code: When creating objects, the String class calculates and caches the hash code of the object, which helps to improve the performance of the hash table.
4. String constant pool in Java is a special memory area used to store string constants. When creating a string constant, the JVM first checks if the same content string already exists in the constant pool. If it does, it simply returns the object from the constant pool, otherwise it creates a new string constant.

Overall, the immutability and other features of the String class make it performant, thread-safe, and user-friendly.