Java For Kids tutorial 5

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.

    { 12, 7, 32, 15, 113, 0, 7 }

Here is how they will be stored with their number in the list:

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.

We can declare arrays in Java in 2 ways:

    int scoreArray[];
    int[] scoreArray;

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.

    int [] scoreArray;
 
    scoreArray = new int[7];

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.

    int[] scoreArray = { 12, 7, 32, 15, 113, 0, 7 };

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

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:

1. what does scoreArray[0] equal?
2. 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:

    nth Element     =>     arrayName[n-1]

If you want to change an array element value, just go something like this:

    scoreArray[3] = 56;
    scoreArray[1] = 27;

To put an array element into another variable, just do something like this:

    int myScore;
    myScore = scoreArray[4];

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

Lets write a program after all that theorizing!

    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]);
        }
    }

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:

Player 1: 23
Player 2: 66
...
Player 11: 7

Runs Per Over = 4.03

Lets first write out the steps that our program will take, in plain English.

1. Declare array of ints containing 11 elements.
2. Loop through these items to read each score - input.
3. Add each score to a total.
4. Calculate the Runs Per Over.
5. Print out the scores.
6. Print out the Runs Per Over.

What we have just done is write the program's

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:

1. Are these statements legal?
   • int[] numberArray[];
   • String[] name;
   • double price[]; price = new double[12];
2. What are the default initialization values for int, double, String, boolean?