/**
 * Examples of using an array as a parameter
 * and as a return type
 */
public class TryArrayParam
{
    public static void main(String [] args)
    {
        // What happens when an int is a parameter?  and a return type?
        int x = 5;
        System.out.println("x = " + x);

        System.out.println("\nRunning changeValue(x), not keeping return value");
        changeValue(x);
        System.out.println("after changeValue(x), x = " + x);    

        System.out.println("\nRunning changeValue(x), using return value to replace x");
        x = changeValue(x);
        System.out.println("after x = changeValue(x), x = " + x); 

        // What happens when an array of ints is a parameter?
        int [] numArray = {1,2,3,4};
        System.out.println("\nBefore changeArray():");
        for (int i = 0; i < numArray.length; i++)
        {
            System.out.print(" numArray[" + i + "] = " + numArray[i]);
        }
        System.out.println();
        System.out.println("Memory address of numArray = " + numArray);

        System.out.println("\nRunning changeArray(numArray), not keeping return value");
        changeArray(numArray);

        System.out.println("After changeArray():");
        for (int i = 0; i < numArray.length; i++)
        {
            System.out.print(" numArray[" + i + "] = " + numArray[i]);
        }
        System.out.println();
        System.out.println("Memory address of numArray = " + numArray);

        // How to take an array and change its number of elements
        numArray = expandArray(numArray);
        System.out.println("\nAfter expandArray():");
        for (int i = 0; i < numArray.length; i++)
        {
            System.out.print(" numArray[" + i + "] = " + numArray[i]);
        }
        System.out.println();  
        System.out.println("Memory address of numArray = " + numArray);
    }

    // Will this method change the value held in the parameter?
    public static int changeValue(int num)
    {
        num = 8;
        return num;
    }

    // Will this method change the value held in the parameter?
    public static void changeArray(int [] list)
    {
        list[0] = 9;
        list[1] = 13;
        list[2] = -4;
        list[3] = 34;
    }
    
    // How to take an an array and change its size, copying what is there
    public static int [] expandArray(int [] source)
    {
        int [] source2X = new int[source.length * 2];
        for (int i = 0; i < source.length; i++)
        {
            source2X[i] = source[i];
        }
        for (int i = source.length; i < source2X.length; i++)
        {
            source2X[i] = 0;
        }     
        System.out.println("\nIn expandArray(), memory address of parameter array = " + source);
        System.out.println("Memory address of bigger array = " + source2X);
        return source2X;
    }
}