Why Java doesn't supply a simple swap function?

Question

Every time I want to swap two values I have to use temporary to do the actual swap. Why doesn't Java give us a facility method in whatever class to simply swap the values of two vars?

Answer 1

Java is Pass-by-Value. That is why you cannot create a simple swap-method (ref).

---

You can however wrap your references inside another object and swap the internal refs:

public static void main(String[] args) {
    Ref<Integer> a = new Ref<Integer>(1);
    Ref<Integer> b = new Ref<Integer>(2);

    swap(a, b);

    System.out.println(a + " " + b); // prints "2 1"
}

public static <T> void swap(Ref<T> a, Ref<T> b) {
    T tmp = a.value;
    a.value = b.value;
    b.value = tmp;
}

static class Ref<T> {
    public T value;

    public Ref(T t) {
        this.value = t;
    }

    @Override
    public String toString() {
        return value.toString();
    }
}

Answer 2

Java does not supply such method because it is not possible. Variables are passed to method by value. Yes, even if these are objects. In this case we pass reference to object by value. Therefore you cannot change value of source variable inside method that received this variable as parameter:

int a = 5;
int b = 6;
swap(a, b);
// a is still 5, b is still 6!


void swap(int first, int second) {
    int tmp = first;
    first = second;
    second = tmp;
}