Thread: Returning multiple values from a method.

Originally Posted by atar

Hi there!!

Just wanted to ask please if this is applicable to return multiple values from a method in java as it is in php's functions for instance.

Thanks in advance!!

Atar.

How would you do this in php? As far as I know, and unless the php docs are out of date, you cannot
PHP: Returning values - Manual

A function can not return multiple values

In java you could effectively do this just as you would in php - by wrapping the values in something else, for instance an array, a Collection, or wrap the values within a particular object.

@copeg

Thank you about your quick response!!

Can you post here a little example about how to do so with arrays, collections that you spoke about?

Your help is appreciated!!

Atar.

@Samaras: that's not necessarily returning a value, you're simply modifying one. I know it's common practice in C, but there are a few caveats with this method.

The first is you can't actually change what array you have, so the array you're passed is the array you have to modify.

For example:

public static void main(String[] args)
{
    int[] a = new int[5];
    doIt(a);
    for(int i = 0; i < a.length; ++i)
    {
        System.out.println(a[i]);
    }
}
 
public static void doIt(int[] var)
{
    var = new int[5];
    for(int i = 0; i < var.length; ++i)
    {
        var[i] = 3;
    }
}

When you run this code, you'll notice that the program prints out five 0's, not five 3's.

The better method is to instantiate and return said array:

public static void main(String[] args)
{
    int[] a = doIt();
    for(int i = 0; i < a.length; ++i)
    {
        System.out.println(a[i]);
    }
}
 
public static int[] doIt()
{
    var = new int[5];
    for(int i = 0; i < var.length; ++i)
    {
        var[i] = 3;
    }
    return var;
}

Note that this code still only returns one value: it's returning an array. However, an array is composed of multiple elements, which can be extracted.

Now if you have to return a bunch of values who's type do not correlate, the best practice is to create a class which holds all of the necessary components. For example, take the following class:

public class Customer
{
    public String name;
    public int id;
    public double pay;
}

Using a similar method as above, you can create and instantiate a Customer object and return it. Again, technically you're only returning one value: a customer object. However, inside that object there is a name, id, and pay fields.

if you return the array or pass it as an argument does not make much difference

What if the called method wants to set the size of the array it returns?

If it is been returned the size is going to change.

There might not be an array passed to the method. It all depends on what the method is supposed to do.
I would change that to say the size of the returned array would be set by the called method.

Args are passed by value.

Start your own thread if you have questions. This one was started by atar.