Computer Science 111 Fundamentals of Computer Programming I

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Computer Science 111Fundamentals of Computer
Programming I

• Introduction to Arrays
• and Color

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(No Transcript)
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The Need for Arrays

• Often we need many different variables that are
  of the same type and play a similar role in the
  program
• For example, suppose we have a temperature
  reading for each day of the year and need to
  manipulate these values several times within a
  program.
• With simple variables,
• We would need to declare 365 variables.
• We would not be able to loop over these variables.

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General Comments about Arrays

• An array is a numbered collection of variables of
  the same type.
• The variables in an array share the same name and
  are distinguished from one another by their
  numbers or subscripts.
• We can loop through the variables of an array by
  using a variable for the subscript.
• The subscripts are always 0,1,, size-1

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Referencing Array Elements

• Suppose we have an array, temperature, for the
  temperature readings for the year.
• The subscripts would be 0,1,,364.
• To refer to the reading for a given day, we use
  the name of the array with the subscript in
  brackets temperature4 for the fifth day.

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Referencing Array Elements (cont)

• To assign the value 89 for the 150th
  day temperature149 89
• We can loop through the elements of an array by
  varying the subscript. To set all of the values
  to 0, say for (i 0 i temperaturei 0

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Declaring an Array

• Like all variables, arrays must be declared
  before being used.
• In declaring an array, we give
• The type of the array elements
• A pair of brackets, , to indicate an array
• The name of the array variable
• For example, int temperature

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Declaring and Creating an Array

• We can declare and create an array of a given
  size as follows
• int temperature new int365
• This creates temperature as an array with space
  for 365 integers.
• Alternatively, we can specify the entries
• double scores 2.1, 3.7, 8.8, 4.7, 5.0
• This creates scores as an array with space for 5
  doubles and with scores 0 2.1, etc.

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The length of an array

• One attribute of an array object is its length
  i.e., the number of elements it can hold.
• The length of an array is stored as a public
  (naughty, naughty) instance variable called
  length.
• temperature.length should give 365

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Disabling buttons

• If we are working with a GUI, there may be times
  when we do not want the user to be able to use a
  certain button. For example, we may not want the
  user to be able to use a Hit button in blackjack
  before any cards have been dealt.
• We can disable and enable buttons as
  follows hitButton.setEnabled(false) dealButton
  .setEnabled(true)

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Color Constants

• To use the java Color class, you should import
  java.awt.
• The Color class has the following constants
• red black
• yellow white
• blue gray
• orange lightGray
• pink darkGray
• cyan
• magenta

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Using a little color with GUIs

• You can do the following, say in a constructor
  chickenButton.setForeground(Color.yellow)
• To color the window itself this.getContentPane(
  ).setBackground(Color.magenta)

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More on color

• RGB colors can be created by specifying their
  red, green and blue components. Each of these is
  specified as a whole number in the range of
  0-255.
• The Color class has a constructor that takes 3
  such numbers and produces the corresponding
  color Color myColor new Color(138,100,86) in
  t redAmt randomInt(0,255) int greenAmt
  randomInt(0,255) int blueAmt
  randomInt(0,255) Color oldWeirdColor new
  Color(redAmt,greenAmt,blueAmt)

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An applet a day...