What is Stateless Object in Java?

Question

Currently I\'m reading \"Java concurrency in practice\", which contains this sentence:

Since the action of a thread accessing a stateless object can\'

Answer 1

If the object doesn't have any instance fields, it it stateless. Also it can be stateless if it has some fields, but their values are known and don't change.

This is a stateless object:

class Stateless {
    void test() {
        System.out.println("Test!");
    }
}

This is also a stateless object:

class Stateless {
    //No static modifier because we're talking about the object itself
    final String TEST = "Test!";

    void test() {
        System.out.println(TEST);
    }
}

This object has state, so it is not stateless. However, it has its state set only once, and it doesn't change later, this type of objects is called immutable:

class Immutable {
    final String testString;

    Immutable(String testString) {
        this.testString = testString;
    }

    void test() {
        System.out.println(testString);
    }
}