[ [[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.
{ 12, 7, 32, 15, 113, 0, 7 }
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:
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.
===== 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:
nth Element => arrayName[n-1]
===== Changing Java Array values =====
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]);
}
}
===== 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:
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.
- 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?