Why String is immutable in Java ?
1. Requirement of String Pool
String pool (String intern pool) is a special storage area in Method Area. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned,
If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.
2. Caching Hashcode
The hashcode of string is frequently used in Java. For example, in a HashMap. Being immutable guarantees that hashcode will always the same, so that it can be cashed without worrying the changes.That means, there is no need to calculate hashcode every time it is used.
3. Facilitating the Use of Other Objects
HashSet<String> set = new HashSet<String>();
if String is mutable, it's value can be changed which would violate the design of set (set contains unduplicated elements).
5. Immutable objects are naturally thread-safe
Because immutable objects can not be changed, they can be shared among multiple threads freely. This eliminate the requirements of doing synchronization.
In summary, String is designed to be immutable for the sake of efficiency and security.
Read full article from Why String is immutable in Java ?
String is an immutable class in Java. An immutable class is simply a class whose instances cannot be modified. All information in an instance is initialized when the instance is created and the information can not be modified.1. Requirement of String Pool
String pool (String intern pool) is a special storage area in Method Area. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned,
If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.
2. Caching Hashcode
The hashcode of string is frequently used in Java. For example, in a HashMap. Being immutable guarantees that hashcode will always the same, so that it can be cashed without worrying the changes.That means, there is no need to calculate hashcode every time it is used.
3. Facilitating the Use of Other Objects
HashSet<String> set = new HashSet<String>();
if String is mutable, it's value can be changed which would violate the design of set (set contains unduplicated elements).
5. Immutable objects are naturally thread-safe
Because immutable objects can not be changed, they can be shared among multiple threads freely. This eliminate the requirements of doing synchronization.
In summary, String is designed to be immutable for the sake of efficiency and security.
Read full article from Why String is immutable in Java ?
