Introduction to arrays

Java arrays allow us to create a contiguous sequence of elements of the same
type. In this sense they are similar to Java String, which is a sequence of 
elements of the same type char.

Just like Java Strings, with Java arrays we can:
- obtain the length
- gain access to an individual element
- use the indices 0..length-1 (inclusive)

In addition, with Java arrays we can:
* modify the contents of individual element (not possible in Java String)

Here is a comparison between Java String and Java array:

STRING                              ARRAY

Creating                            Creating

String word = "hello";              int[] numbers = {5, 3, 6, 2};
                                    double[] scores = {3.3, 4.0, 2.0};
                                    char[] letters = {'h', 'e', 'l', 'l', 'o'};
                                    String[] words = {"how", "are", "you"};
                                    boolean[] answers = {true, false, false, true};

Getting the length                  Getting the length

word.length()                       numbers.length     <-- no parentheses ()
                                    scores.length
                                    letters.length
                                    words.length
                                    answers.length

Valid indices                       Valid indices

0..word.length()-1 (inclusive)      0..numbers.length-1 (inclusive)


Accessing an element                Accessing an element

word.charAt( integer-index )        numbers[ integer-index ]


Modifying an element                Modifying an element

NOT POSSIBLE                        int[] numbers = {5, 3, 6, 2};

                                    int x = numbers[0]; // x is now 5
                                    numbers[3] = 2*x;   // last element now 10

                                    numbers[1] = numbers[2];

                                    // numbers is now {5, 6, 6, 10}


When the size of the  array is  known in advance we 
can create an array of the given number of elements:

int[] myArray = new int[10];         // myArray has 10 empty slots

int size = myArray.length/2;
int[] yourArray = new int[size];     // yourArray has 5 empty slots


Note that in the examples above we can replace int with any other type before the []:

char[] letters = {'s', 'm', 'i', 'l', 'e', 'y'};                 boolean[] answers = {true, false, false, true};

char c = letters[0]; // c is now 's'                             boolean q1 = answers[0]; // q1 is now  true
letters[5] = '!';    // last element now '!'                     answers[3] = false;      // last element now  false

letters[0] = letters[4];                                         answers[0] = answers[3];

// letters is now {'e', 'm', 'i', 'l', 'e', '!'}                 // answers is now {false, false, false, false}

char[] myArray = new char[10];                                   boolean[] myArray = new boolean[10];

int size = myArray.length/2;                                     int size = myArray.length/2;
char[] yourArray = new char[size];                               boolean[] yourArray = new boolean[size];