ArraysAfter a while

Remember for loops?

for(int i = 0; i < 10; i++){System.out.println(i);

}

-But what if we are unsure of how many cycles we need?

1. declare and define a counter variable

2. boolean condition, checked every iteration

3. update counter variable every iteration

while loops

• Allow us to loop for an indeterminate amount of cycles• Example:

while(door.isLocked()){ringDoorBell();waitForResponse(10);

}

New Keywordboolean condition inside parentheses

Curly braces encompass code to be cycled over

Beware of infinite loops!

• If the boolean condition of a while loop is always true, the loop will never exit

• This is called an infinite loop and can be a really annoying bug to fix

• Used to cause computers to freeze, now OS’s are more robust

• Still bad news for your program

A Problem

• Until now, we have used variables that hold a single object/value• What if we want to hold lots of data?• Imagine trying to store the first 20 numbers of the Fibonacci sequence? int _firstNum;

int _secondNum; int _thirdNum;

...int _twentiethNum;

• This is annoying, and what about storing the first 1,000 or 1,000,000?

Arrays to the rescue!

• Arrays store a specified number of homogenous(same type) data elements (variables)• You can refer to a specific element by its index• Indexing starts at 0 and ends at the size of the array – 1• This is a visualization of an array of size 20:

Real life “arrays”

Array Syntax

• Declaration:

int[] fibNumbers;

• Definition pt. 1:

fibNumbers = new int[5];

Type of variable the array will hold

Square bracketsdenote array Array Name

Array size

Initializing Elements of the array

• Definition pt.2:

fibNumbers[0] = 1;fibNumbers[1] = 1;fibNumbers[2] = 2;fibNumbers[3] = 3;fibNumbers[4] = 5;

But wait a minute, this isn’t any better than before!

A Cleverer Way to Initialize

• Using a for loop to initialize the elements of an array is much better

• Let’s do this for the Fibonacci sequence