[ACCEPTED]-Is it possible to write swap method in Java?-primitive-types

While it is not possible to write a function 12 that simply swaps two variables, it is possible 11 to write a helper function that allows you to:

• Swap two variables using only one statement
• Without temporary variables in the caller's code
• Without 'boxing' primitives
• With a few overloads (one of them using generics), it works for any type

That's how 10 you could do it:

int returnFirst(int x, int y) {
    return x;
}
int a = 8, b = 3;
a = returnFirst(b, b = a); // try reading this as a = b; b = a;
System.out.println("a: " + a + ", b: " + b); // prints a: 3, b: 8

This works because the Java 9 language guarantees (Java Language Specification, Java 8 SE 7 Edition, section 15.12.4.2) that all 7 arguments are evaluated from left to right 6 (unlike some other languages, where the 5 order of evaluation is undefined), so the 4 execution order is:

1. The original value of b is evaluated in order to be passed as the first argument to the function
2. The expression b = a is evaluated, and the result (the new value of b) is passed as the second argument to the function
3. The function executes, returning the original value of b and ignoring its new value
4. You assign the result to a

If returnFirst is too long, you 3 can choose a shorter name to make code more 2 compact (e.g. a = sw(b, b = a)). Use this to impress your 1 friends and confuse your enemies :-)

Without using an array or objects, no, it 1 is not possible to do it within a method.

Check out this JavaWorld article that explains 7 it in detail:

http://www.javaworld.com/javaworld/javaqa/2000-05/03-qa-0526-pass.html

A swap of two primitives will 6 never work because primitives are passed 5 by value in Java. You can't even write a 4 method to swap two objects for that matter.

Like 3 @Thomas said, the only thing you could do 2 is have your primitives contained within 1 other objects/arrays and modify those.

One-liner for any primitive numbers:

a += (b - (b = a));

0

You can make a generic version of @marcus's 2 swap method that swaps any number of objects 1 of the same type:

<T> T swap(T... args) {   // usage: z = swap(a, a=b, b=c, ... y=z);
    return args[0];
}

b = swap(a, a=b);
z = swap(x, x=y, y=z);

In java5, the closest I can think of, which 2 may help you, is :

The AtomicInteger class 1 (and others) have getAndSet() atomic methods ..

To write a swap method that swaps primitives 4 you'd have to have the concept of "out" variables, i.e. variables 3 whose values are passed up to the calling 2 context. C# has those but you must still 1 specify that they're out variables.

This function will swap two ints

Integer[] swap(int a, int b){
    return new Integer[]{b,a};
}

0

Here's a method that swaps two primitive 4 variables

private void swap(){
    int a = 1;
    int b = 2;
    int temp = a;
    a = b;
    b = temp;
}

It might not be of much use though 3 ;)

Ok seriously, it could be done if the 2 variables are class level:

public class MyClass{
    // excuse horrible coding practice of public mutable fields
    public int a = 1;
    public int b = 2;

    public void swap(){
        int temp = a;
        a = b;
        b = temp;
    }
}

Again though, I 1 fail to see what the use of this could be

I have read the above answers seeking an 4 explanation as to why it is said that a 3 swapping program cannot be written in java 2 in the way it is written in c++. I did 1 the following way program screenshot

As Thomas Owens said. You could probably 2 do it in C by passing variables by &reference, but 1 afaik not in Java without using objects.