Arrays.java

import java.util.Random;
 
public class Arrays {    
    public static void main(String[] args) {
        // Declaration style. 
        int arrayTwo[] = new int[3];
        int[] arrayOne = new int[3];   // This is better! []'s are part of the type!!

        // Indexing: We always refer to the first element of an array [0].
        // ex. subway example
        String[] suits = { "Clubs", "Diamonds", "Hearts", "Spades" }; 
        System.out.println("suits[3]=" + suits[3]);
        System.out.println();

        // Length: Once we create an array, its size is fixed.
        String[] ranks = { "2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King", "Ace" };
        System.out.println("suits.length=" + suits.length);
        System.out.println();

        // When you create an array, Java reserves space in memory for it.
        // Random access! Contiguous memory! Important property.
        int x = new Random().nextInt(ranks.length); // Generate a random int less than ranks.length
        int y = new Random().nextInt(suits.length); // Generate a random int less than suits.length
        System.out.println(ranks[x] + " of " + suits[y] + "\n");
        System.out.println();

        // We can hard-code the length, or initialize an array with a value at runtime.
        String[] deck = new String[ranks.length * suits.length]; // vs [52]
        for (int i = 0; i < ranks.length; i++) {
            for (int j = 0; j < suits.length; j++) {
                deck[suits.length * i + j] = ranks[i] + " of " + suits[j];
            }
        }

        // Arrays can be multi-dimensional!
        int[][] twoD = new int[][] {
          {1, 2, 3, 4},
          {5, 6, 7, 8}
        };
        // What does this print?
        System.out.println("twoD[1][2]=" + twoD[1][2]);

        // What will this print? Why?
        System.out.println(deck);
        System.out.println();

        // or.. what happens if I use a negative number to index an array?

        // What happens if I do this?
        for (int j = 0; j <= suits.length; j++) {
            System.out.println("suits[j]=" + suits[j]);
        }

        // WARNING!! A little advanced.

        // Returning arrays from methods.
        int[] array = makeArray();
        for (int i : array) {
            System.out.print(i + " ");
        }
    }

    public static int[] makeArray() {
        // Created on the heap! This is why it doesn't disappear when the stack frame is popped.
        int[] myArray = new int[10];  // new == heap
        for (int i = 0; i < myArray.length; i++) {
            myArray[i] = i;
        }
        return myArray;
    }

}