Intro to Java

1
Intro to Java

• while loops
• pseudocode

2
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
• Java has 3 loop statements while, do, for

3
Syntax of the while statement
while (condition) statement

• condition is a true/false (boolean) expression
• statement is a single or block statement
• If condition is initially false, the statement is
  never executed
• If the condition is true, the statement is
  executed. Repeat this step.
• The statement should eventually make the loop
  stop (unless you want to have an infinite loop)

4
A while Loop to Print Numbers

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

5
An Infinite Loop

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

6
More Infinite Loops

• // Some infinte loops are intentional
• while (true)
• statement(s)
• // Others are not
• int x 5
• while (x lt 10)
• statement(s) which dont change x

7
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
• process bots
• update game state
• determine if game should end
• if game should be saved
• save game
• quit

8
A while Loop for Powers of 2

• // Computes 2 pow. Assumes pow gt 0.
• int result 1
• while (pow gt 0)
• result result 2
• pow pow - 1
• System.out.println(result is result)