/**
 * Arrays are covariant in Java. Hence, you can pass 
 * Integer[] into changeN and printArr methods. But you cannot pass
 * Number[] into changeI.
 * Likewise you can assign a Number[] to a var of type integer[]
 * but not the opposite
 * 
 * @author: gtowell
 * created: July 2022 
 */
public class ArraCov {

    /**
     * Set the values in an Integer[].
     * NOTE: side effects abound (as per functional programming)
     * Note use of autoboxing
     * @param iArr the array to be set
     */
    private void changeI(Integer[] iArr) {
        for (int i = 0; i < iArr.length; i++)
            iArr[i] = i;
    }

    /**
     * Set the values in a Number[]
     * Because of covariance, can pass an Integer array in to this
     * function. But then I can try to put a non-integer into  the
     * integer array ... BAD
     * @param nArr the array to be set
     */
    private void changeN(Number[] nArr) {
        for (int i = 0; i < nArr.length; i++)
            nArr[i] = i+13.2;
    }

    /**
     * Print the contents of the passed array
     * @param nArr the passed array
     */
    public void printArr(Number[] nArr) {
        for (int i = 0; i < nArr.length; i++)
            System.out.println(i + "  " + nArr[i]);
    }
    
    /** 
     * Testing function for covariant arrays
     */
    public void test() {
        Number[] nArr = new Number[5];
        Integer[] iArr = new Integer[5];
        nArr = iArr;
        for (int i = 0; i < nArr.length; i++) {
            nArr[i] = Double.valueOf(i + 10.5);
            iArr[i] = Integer.valueOf(i);
        }
        printArr(nArr);
        printArr(iArr);
        //changeI(nArr); // will not compile
        changeN(nArr);
        changeN(iArr);
        printArr(nArr);

        nArr = iArr;
        //iArr = nArr; // will not compile
    }

    /**
     * Testing function for variant types
     */
    private void test0() {
        Number nl;
        Integer ii = Integer.valueOf(3);
        nl = ii;
        nl = Double.valueOf(3.5);
        System.out.println(nl + " " + ii);
    }

    public static void main(String[] args) {
        //new ArraCov().test0();
        new ArraCov().test();
    }
}