In Java, what is the difference between the following declarations?

Question

Browse Java. How are these 2 different and why?

public void languageChecks() {
    Integer a = 5;
    Integer b = new Integer(5);

    change(a); // a doesn't get incremented. value is 5
    change(b); // b does. value is now 6
}

public void change(Integer a) {
    a++;
}

Answer 1

The only difference is that

Integer b = new Integer(5);

guarantees the creation of a new facility. The first will use the cache instance (see Integer.valueOf()).

Both are immutable, and references to both are passed by value (like everything in Java). Therefore, change()does not affect.

Answer 2

, a++ a = a + 1, a , . Integer, ( ), ints, .

Answer 3

No call to change () affects the passed values ​​due to automatic boxing / unpacking.

public void change(Integer a) {
    // This unboxes 'a' into an int, increments it and throws it away
    a++;
}

The above code means that a ++ changes the value of a since it is an object, not a primitive. However, ++ is not overloaded by Integer, so it blocks it in order to be able to apply the ++ operator to its int. To me, the compiler should not allow this.