Thread Safety

Requirements to make a class immutable.

• All class variables are private.
• All class variables are immutable.
• No methods other than the INIT block to set class variables.
• the INIT block is not called except in the INIT block.
• All fields are private.
• All fields are immutable.
• No methods other than the constructor to set fields.

Do not assume that a class is immutable unless the class documentation says so.

Requirements to make the program thread-safe.

• The all methods in an immutable class is thread-safe.
• The methods that update class variables are not thread-safe. A lock is needed to make the method thread-safe.
• The methods that update fields of the object created by other threds are not thread-safe. A lock is needed to make the method thread-safe.