// This class contains several small examples of array manipulation.  Each
// is written as a method.

import java.util.*;

public class ArraySample1 {
    public static void main(String[] args) {
        showArgs(args);

        // In exploring value semantics vs reference semantics, we saw that
        // this swap method did not change the values of x and y
        int x = 3;
        int y = 7;
        swap(x, y);

        // below is an example of an array initializer
        int[] list = {3, 19, 42, 73, 208, 94, 15, 5};

        // we used Arrays.toString to print this array:
        System.out.println("list = " + Arrays.toString(list));

        // we wrote a method to sum a list:
        System.out.println("sum of list = " + sum(list));

        // we saw that the method call below changed the contents of the array
        destroy(list);
        System.out.println("after destroy, list = " + Arrays.toString(list));
        
        // and we wrote this method for reversing the contents of the array
        reverse(list);
        System.out.println("after reverse, list = " + Arrays.toString(list));
    }

    // method to show the contents of the "args" String array
    // This method only showed actual contents when we went into a terminal
    // window and ran the program in this way:
    //     java ArraySample1 these words become the args
    public static void showArgs(String[] args) {
        System.out.println("args length = " + args.length);
        for (int i = 0; i < args.length; i++) {
            System.out.println("args[" + i + "] = " + args[i]);
        }
        System.out.println();
    }

    // we saw that this is correct code for swapping two int values, but it
    // only swaps the local copies of these values and has no effect on any
    // variables that are used in calling the method
    public static void swap(int x, int y) {
        int temp = x;
        x = y;
        y = temp;
    }

    // we saw that this method was able to change the array contents because
    // of reference semantics
    public static void destroy(int[] list) {
        list[0] = -924;
        list[1] = -42;
    }

    public static int sum(int[] list) {
        int sum = 0;
        // traversal pattern
        for (int i = 0; i < list.length; i++) {
            sum += list[i];
            // do something with list[i]
        }
        return sum;
    }

    // this method reverses the sequence of values in an array
    public static void reverse(int[] list) {
        // we found that we only wanted to do the swapping for half of the
        // length of the list (otherwise we unreversed it)
        for (int i = 0; i < list.length / 2; i++) {
            // swap two values
            int temp = list[i];
            list[i] = list[list.length - 1 - i];
            list[list.length - 1 - i] = temp;
        }
    }
}