Introduction to Programming with Java, for Beginners

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Introduction to Programmingwith Java, for
Beginners

• Control Structures

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Sequential Control Flow

• Consists of just a list of commands to be done in
  order
• Welcome to Dr. Java
• int x 2
• int squareOfX x x
• System.out.println(x) //Or just type
  squareOfX
• 2

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What are control Structures ?

• You cant do very much if your program consists
  of sequential control flow
• The program cannot choose whether or not to
  perform a command
• The program cannot perform the same command more
  than once
• Such programs are extremely limited!
• Control structures allow a program to base its
  behavior on the values of variables

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Recap Boolean

• Boolean is one of the eight primitive types
• Booleans are used to make yes or no decisions
• All control structures use Booleans
• There are exactly two Boolean values, true
  (yes) and false (no)
• Boolean, true, and false are all lowercase
• Boolean variables are declared like any other
  kind of variable
• Boolean hungry
• boolean passingGrade
• boolean taskCompleted false

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Numeric Boolean Comparisons

• The following comparisons each give a Boolean
  result
• (25 24) (12 13) //results to false
• (25 24) (12 13) //results to true

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Conditionals (if statements)

• An if statement is a flow control statement
• It is also called a conditional, or a branch
• Well see several flavors
• An if all by itself
• An if with an else part
• An if with an else if part

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if statement
if (condition) statement(s)

• If the condition is true, then the statement(s)
  (i.e. instructions) will be executed. Otherwise,
  it/they wont.

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if-else statement
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Cascading if-else
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Nested if-statements
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The infamous dangling else

• An else is paired with the last else-less if,
  regardless of spacing, unless dictate
  otherwise.

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A Loop

• A simple but powerful mechanism for making lots
  of things happen!
• Performs a statement (or block) over over
• Usually set up to repeat an action until some
  condition is satisfied, e.g.
• Run an application until user hits quit button
• Read characters until end of file reached
• Deal card hands until game over

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Syntax of the while statement
while (condition) statement(s)

• condition is a true/false (boolean) expression
• If condition is initially false, the statement is
  never executed
• If condition is true, statement is executed and
  condition is re-evaluated
• The statement should eventually make the loop stop

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A while Loop to Print Numbers

• // Print the numbers 1 thru 10
• int x 1
• while (x
• System.out.println(x)
• x x 1

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An Infinite Loop

• // Faulty attempt to print 1 thru 10
• int x 1
• while (x
• System.out.println(x)

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More Infinite Loops

• // Some infinte loops are intentional
• while (true)
• statement(s)
• // Others are not
• int x 5
• while (x
• statement(s) which dont change x

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Pseudocode and Loops
Pseudocode is an informal, english-like,
code-like way Of sketching out what you want your
code to do.

• initialize game
• while( the game isnt over)
• process player input
• update game state
• determine if game should end
• if game should be saved
• save game
• quit

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Compute Square of first 10 numbers

• //In Square.java
• int number 1
• int squareOfNumber 0
• while (number
• squareOfNumber number number
• System.out.println(number " "
  squareOfNumber)
• number number 1

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For Loop

• for (init end-test re-init) statement
• Executes loop body as long as end-test evaluates
  to TRUE
• Initialization and re-initialization code
  included in loop statement
• Note Test is evaluated before executing loop body

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While vs. For
Note For loops are used generally for bounded
iteration
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Summary of Loops
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Indentation

• if(x
• else___xx-1
• while(x0)___System.out.println(x)___xx
  -1

• Recommended indentation is from 2 to 4 spaces,
  but must be consistent throughout the program
• Most important style rule If you are modifying
  or adding to an existing program, keep to the
  original style (whatever it may be)