Introduction to Programming with Java, for Beginners

1
Introduction to Programmingwith Java, for
Beginners

• Conditionals (if statements)

2
Conditionals (if statements)

• An if statement is a flow control 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
• A cascading series of the above
• First, well look at some examples then well
  look at
• the syntax (grammar rule)

3
Examples of if statements
// assume x and max are ints if (x gt max) max x
boolean result // assume code here sets result to be true or false if (result true) // if (result) System.out.println(result is true.) else System.out.println(result is false.)
4
if statement
if (condition) statement
if (condition) statement(s)

• If the condition is true, then the statement(s)
  will be executed.
• Otherwise, they wont.

5
Example how to swap
int num1 40 int num2 20 // Let num1 store the smaller if (num1 gt num2) int temp 0 temp num1 num1 num2 num2 temp Heres how to swap the values of two variables by using a temporary variable. This is a common pattern used for swapping all kinds of data.
6
if-else statement
Example Syntax Explanation
int x 5 int y 10 int min -9999 if (x lt y) min x else min y if (condition) statement(s) else statements(s) If the condition is true, then the statement(s) in the if block are executed. Otherwise, if there is an else part, the statement(s) in it are executed.
7
Cascading if-else
Example
char userChoice // Ask user for input and store it in userChoice if (userChoice q) System.out.println(quitting.) else if (userChoice a) System.out.println(adding.) else if (userChoice s) System.out.println(saving.) else System.out.println(unrecognized choice.)
8
Nested if-statments
An if within an if Truth Table
if (condition1) if (condition2) statement(s) A else statement(s) B else statements(s) C What values must the conditions have in order for block A to run? B? C?
A B C
condition1 T
condition2
9
The infamous dangling else
Code Notes
if (condition 1) if (condition 2) statementA else statementB When is statementB executed? In other words, which if is the else paired with?

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

if (condition 1) if (condition 2) statementA else statementB