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[ [[tutorial-en-001 | Intro]]    | [[tutorial-en-002 | Begin]] |
[[tutorial-en-003 | if/else]]    | [[tutorial-en-004 | Loops]] |
[[tutorial-en-005 | Arrays]]     | [[tutorial-en-006 | Graphics]] |
[[tutorial-en-007 | Animation]]  | [[tutorial-en-008 | Mouse]] |
[[tutorial-en-009 | Game]]       | [[tutorial-en-010 | Real]] |
[[tutorial-en-011 | Methods]]    | [[tutorial-en-012 | Class]] |
[[tutorial-en-013 | Class 2]]    | [[tutorial-en-014 | Applet]] |
[[tutorial-en-015 | MouseClick]] | [[tutorial-en-016 | Thread]] |
[[tutorial-en-017 | Button]]     ]
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====== Java For Kids tutorial 5 ======

===== Arrays =====
Arrays are lists of similar objects or datatypes. They are ordered
in a numbered sequence starting from 0 until the end or last item in the array.
Here is an array of integers (int's). Note the format.
<code java>
    { 12, 7, 32, 15, 113, 0, 7 }
</code>

Here is how they will be stored with their number in the list:
^  index  |  0   |  1  |  2   |  3   |  4    |  5  |  6  |
^  value  |  12  |  7  |  32  |  15  |  113  |  0  |  7  |

The array items' number in the list is called its index.
To get the value of an array item  or element you give its index
inside [ ] square brackets after the array's name. We could call
the above array scoreArray.

===== Declaration of Arrays =====
We can declare arrays in Java in 2 ways:
<code java>
    int scoreArray[];
    int[] scoreArray;
</code>

This declaration tells the compilers what type of variables (datatype)
the array contains. No actual array is created until the keyword NEW is
invoked or used. E.g.
<code java>
    int [] scoreArray;

    scoreArray = new int[7];
</code>

The 2 lines above put an array of 7 ints into the array called scoreArray
and they are all given a default value of 0.

An array can be declared, constructed, and initialized in a single
statement. e.g.
<code java>
    int[] scoreArray = { 12, 7, 32, 15, 113, 0, 7 };
</code>

Note the use of the { } curly brackets and commas between the elements
of the array.

===== Calling an Array Element =====
To retrieve an element in an array we simply put its index number in square brakets []
after the array name. e.g. scoreArray[0];

** Exercise: **
  - what does scoreArray[0] equal?
  - What is the value of scoreArray[5]?

Remember - arrays start at index 0. So, the 5th element in an array
will be arrayName[4].

Here is a formula:
<code java>
    nth Element     =>     arrayName[n-1]
</code>

===== Changing Java Array values =====
If you want to change an array element value, just go something like this:
<code java>
    scoreArray[3] = 56;
    scoreArray[1] = 27;
</code>

To put an array element into another variable, just do something like this:
<code java>
    int myScore;
    myScore = scoreArray[4];
</code>

If you printed out myScore (printLine(myScore);), it would print 113.

Lets write a program after all that theorizing!
<code java>
    void main() {
        // declare, initialize array
        int[] scoreArray = { 12, 7, 32, 15, 113, 0, 7 };

        // print scores
        for (int i = 0; i<7; i++)
        {
            printLine("Score "+ i + " = " + scoreArray[i]);
        }
    }
</code>

===== Java Problem: =====
You have been given the job by the ACB to write a program to enter
the scores for the Australian cricket teams one day match scores.

Output the scores and the Runs Per Over. A One Day Game has 50 overs.

It could have an output like this:
<code>
Player 1: 23
Player 2: 66
...
Player 11: 7

Runs Per Over = 4.03
</code>

Lets first write out the steps that our program will take, in plain English.
  - Declare array of ints containing 11 elements.
  - Loop through these items to read each score - input.
  - Add each score to a total.
  - Calculate the Runs Per Over.
  - Print out the scores.
  - Print out the Runs Per Over.

What we have just done is write the program's

===== ALGORITHM =====
An Algorithm is the series of steps written in plain English that would
make our program run successfully or accomplish its task.

Lets write it! You have a go on your own first.

...

What did you get?

...

...

When you have done it, try to read in and output each cricketer's name
instead of Player 3 e.g.

Calculate the Average score for the team.

And print out those above it and those below the average.

Exercise:
  - Are these statements legal?
    * int[] numberArray[];
    * String[] name;
    * double price[]; price = new double[12];
  - What are the default initialization values for int, double, String, boolean?