Why isn't it an error?

The following program is a recursive program to find the maximum and minimum of an array.(I think! Please tell me if it is not a valid recursive program. Though there are easier ways to find the maximum and minimum in the array, I'm doing in the recursive manner only as a part of a exercise!)

This program works correctly and produces the outputs as expected.

In the comment line where I have marked "Doubt here!", I am unable to understand why an error is not given during compilation. The return type is clearly an integer array (as specified in the method definition), but I have not assigned the returned data to any integer array, but the program still works. I was expecting an error during compilation if I did it this way, but it worked. If someone would help me figure this out, it'd be helpful! :)

import java.io.*;
class MaxMin_Recursive
{
    static int i=0,max=-999,min=999;
    public static void main(String[] args) throws IOException
    {
        BufferedReader B = new BufferedReader(new InputStreamReader(System.in));
        int[] inp = new int[6];
        System.out.println("Enter a maximum of 6 numbers..");
        for(int i=0;i<6;i++)
            inp[i] = Integer.parseInt(B.readLine());
        int[] numbers_displayed = new int[2];
        numbers_displayed = RecursiveMinMax(inp);
        System.out.println("The maximum of all numbers is "+numbers_displayed[0]);
        System.out.println("The minimum of all numbers is "+numbers_displayed[1]);
    }
    static int[] RecursiveMinMax(int[] inp_arr)     //remember to specify that the return type is an integer array 
    {   
        int[] retArray = new int[2];
        if(i<inp_arr.length)
            {
                if(max<inp_arr[i])
                    max = inp_arr[i];
                if(min>inp_arr[i])
                    min = inp_arr[i];
                i++;
                RecursiveMinMax(inp_arr);       //Doubt here!
            }
        retArray[0] = max;
        retArray[1] = min;
        return retArray;
    }
}
Jon Skeet
people
quotationmark

The return type is clearly an integer array (as specified in the method definition), but I have not assigned the returned data to any integer array, but the program still works.

Yes, because it's simply not an error to ignore the return value of a method. Not as far as the compiler is concerned. It may well represent a bug, but it's a perfectly valid use of the language.

For example:

Console.ReadLine(); // User input ignored!
"text".Substring(10); // Result ignored!

Sometimes I wish it could be used as warning - and indeed Resharper will give warnings when it can detect that "pure" methods (those without any side-effects) are called without using the return value. In particular, call which cause problems in real life:

  • Methods on string such as Replace and Substring, where users assume that calling the method alters the existing string
  • Stream.Read, where users assume that all the data they've requested has been read, when actually they should use the return value to see how many bytes have actually been read

There are times where it's entirely appropriate to ignore the return value for a method, even when it normally isn't for that method. For example:

TValue GetValueOrDefault<TKey, TValue>(Dictionary<TKey, TValue> dictionary, TKey key)
{
    TValue value;
    dictionary.TryGetValue(key, out value);
    return value;
}

Normally when you call TryGetValue you want to know whether the key was found or not - but in this case value will be set to default(TValue) even if the key wasn't found, so we're going to return the same thing anyway.

people

See more on this question at Stackoverflow