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What classes are immutable?
Immutable class means once the object of the class is created its fields cannot be modified or changed. In Java, all the wrapper classes like Boolean, Short, Integer, Long, Float, Double, Byte, Char, and String classes are immutable classes.
How do you know if a class is immutable?
It’s properly constructed ( this reference doesn’t leak from constructor) Object state cannot be modified (so class should not have setters and mutator methods) Don’t store external (passed to constructor) references to mutable objects (e.g. create defensive copy of passed collection argument)
What does it mean for a class to be immutable?
At a fundamental level: immutable classes define objects which, once created, never change their value. A variable of an immutable type may only be changed by re-assigning to that variable. When we wish to only modify some portion of an immutable class, we are compelled to reassign the whole object.
Is random class immutable?
So, to answer the question in the title: yes, a class referencing a Random object can be immutable, if the state of the Random object is not observable in the state of the class itself. But this is question of terminology, while immutability is more about how you can use objects.
What is difference between Singleton and immutable class?
Immutable means the value once assigned cannot be changed, so usually you won’t have setter methods in immutable, but no such requirement is there for singleton. But a singleton is more from memory perspective, only one instance will live.
Can a mutable class be a singleton?
A singleton can be mutable or immutable; a non-singleton can be mutable or immutable. However, a singleton must be thread-safe if used in multiple threads; immutable objects are inherently thread-safe.
How to maintain immutability of a class with a mutable object?
Avoid methods which can change the mutable object. So in your example Employee class is immutable, because once it is created, you can’t change its state, because it has only getter methods. Address class is mutable because you can modify it with the setStreet method.
Which is an example of an immutable class in Java?
Immutable objects are those objects whose states cannot be changed once initialized. Sometimes it is necessary to make an immutable class as per the requirement. For example, All primitive wrapper classes (Integer, Byte, Long, Float, Double, Character, Boolean and Short) are immutable in Java. String class is also an immutable class.
Can a class be immutable if it has a private?
So, I read somewhere that there are 3 requirements for a class to be immutable in Java. All data fields must be private. There can’t be any mutator methods for data fields. No accessor methods can return a reference to a data field that is mutable.
Why are all properties of an immutable object final?
A thread-safe immutable object is seen as immutable by all threads, even if a data race is used to pass references to the immutable object between threads. This can provide safety guarantees against misuse of an immutable class by incorrect or malicious code. final fields must be used correctly to provide a guarantee of immutability.