Arrays

1
Arrays

• Rows and rows and rows

2
Arrays

• A contiguous collection of cells
• Cells are also known as elements, items,
  entries, slots
• Each cell contains the same type of item
• The number of cells in an array will never
  change!
• Cells are given names (in a sense)
• Indices (subscripts) beginning at 0

3
Arrays

• When using arrays
• First create the array itself. Must specify
  size!
• Second place data in each slot
• Third relax
• Syntax for declaring an array variable
• ClassName variableName
• Syntax for creating an array
• new ClassName ArraySize

http//www.stephenadams.freeserve.co.uk/2000/graph
ics/policeman.jpg
4
Arrays

• Syntax for accessing an element of the array
• arrayVariable index
• The index must be between 0 and the length of the
  array 1.
• Syntax for replacing an element of the array
• arrayVariable index someExpression
• The index must be between 0 and the length of the
  array -1
• Type conformance rules are still followed
• Syntax for finding the length of an array
• arrayVariable.length

5
Array Example
int numbers int number numbers new
int3 numbers0 1 numbers1
-1 numbers2 numbers0numbers1 numbersnu
mbers2 numbers1 number numbers1
6
Array Examples
Rectangle rects new Rectangle4 rects0
new Rectangle(10, 20, 30, 40) rects1 new
Rectangle(0, 0, 100, 100) rects2
rects1 Rectangle oneRect new Rectangle(10,
10, 10, 10) rects3 oneRect oneRect
rects0
char bunchOfChars new char20 bunchOfChars0
A bunchOfCharsbunchOfChars.length-1
?
7
Arrays

• Can be passed to functions and returned from
  functions
• Problem write a method that takes an array of
  Rectangle objects and sets all of their colors to
  red

private void colorAllRed( Rectangle rects )
for(int i0 iltrects.length i)
rectsi.setColor( Color.red )
Rectangle someRects someRects new
Rectangle3 someRects0 new
Rectangle(0,0,5,5) someRects1 new
Rectangle(6,6,8,8) someRects2 new
Rectangle(10,10,10,10) colorAllRed( someRects )
8
Initializing arrays

• Arrays can be filled with data when declared

int arr 10, 100, 1000 Oval circles
new Oval(1,1,1,1), new Oval(2,2,2,2)
int arr new int3 arr0 10 arr1
100 arr2 1000 Oval circles new
Oval2 circle0 new Oval(1,1,1,1) circle1
new Oval(2,2,2,2)
9
Arrays

• Arrays are Objects (mostly)
• Arrays are not Objects in the normal sense
• Cannot be subclassed
• Hence cannot override methods like toString and
  equals

public class MyArraySubclass extends int
public boolean equals(Object other)
10
Examples

• Write a program to sum the elements in an array
  of doubles.

public double sum(double values) double
result 0 for(int i0 iltvalues.length i)
result valuesi return result
11
Examples

• Write a function that accepts an array of doubles
  named A and a double named V. The function
  returns the index of the first occurrence of V in
  A or -1 if X is not in A.

public int indexOf(double a, double v)
for(int i0 ilta.length i) if(v
ai) return i return -1
12
Examples

• Write a function that accepts an array of doubles
  named A and a double named V. The function
  returns an array of all elements of A that are
  greater than V.

public double greaterThan(double a, double v)
int count0 for(int i0 ilta.length i)
if(ai gt v) count double result
new doublecount int resultIndex 0 for(int
i0 ilta.length i) if(ai gt v)
resultresultIndex ai return result
13
Examples

• Write a function that accepts an array of ints
  and shuffles them into a random order.
• Do the following 2n times, where n is the number
  of elements in the array
• select to random indices into the array and swap
  the elements in the array

public void shuffle(int values) for(int i0
iltvalues.length2 i) int ranIndex1
(int)(Math.random()values.length) int
ranIndex2 (int)(Math.random()values.length) i
nt tmp valuesranIndex1 valuesrandIndex1
valuesranIndex2 valuesrandIndex2 tmp
int data 1,2,3,4,5 shuffle(data)
14
Examples

• Write a function that accepts an array of ints
  and returns the smallest index of the smallest
  value

/ _at_pre values.length gt 1 / public int
findMin(int values) int minIndex
0 for(int i1 iltvalues.length i)
if(valuesi lt valuesminIndex) minIndex
i return minIndex
15
Tic Tac Toe

• Write a TicTacToeModel using arrays!