1. Java Programming Fifth Edition
Chapter 5
Making Decisions

2. Java Programming, Fifth Edition

3. Java Programming, Fifth Edition

4. Making Decisions with the if and if...else Structures
if statement
Simplest statement to make decision
Boolean expression appears within parentheses
Space between keyword if and opening parentheses
Execution always continues to next independent statement
Use double equal sign (==) to determine equivalency
Java Programming, Fifth Edition

5. Making Decisions with the if and if...else Structures (continued)
Java Programming, Fifth Edition

6. Pitfall: Misplacing a Semicolon in an if Statement
No semicolon at end of first line of if statement
if (someVariable == 10)
Statement does not end there
When semicolon follows if directly
Empty statement contains only semicolon
Execution continues with the next independent statement
Java Programming, Fifth Edition

7. Pitfall: Misplacing a Semicolon in an if Statement (continued)
Java Programming, Fifth Edition

8. Pitfall: Using the Assignment Operator Instead of the Equivalency Operator
Attempt to determine equivalency
Using single equal sign
Rather than double equal sign
Illegal
Can store Boolean expression’s value in Boolean variable
Before using in if statement
Java Programming, Fifth Edition

9. Pitfall: Attempting to Compare Objects Using the Relational Operators
Use standard relational operators to compare values of primitive data types
Not objects
Can use equals and not equals comparisons (== and !=) with objects
To compare objects’ memory addresses instead of values
Java Programming, Fifth Edition

10. The if...else Structure Single-alternative if Dual-alternative if
Only perform action, or not
Based on one alternative
Dual-alternative if
Two possible courses of action
if...else statement
Performs one action when Boolean expression evaluates true
Performs different action when Boolean expression evaluates false
Java Programming, Fifth Edition

11. The if...else Structure (continued)
if...else statement (continued)
Statement that executes when if is true or false ends with semicolon
Vertically align keyword if with the keyword else
Illegal to code else without if
Depending on evaluation of Boolean expression following if
Only one resulting action takes place
Java Programming, Fifth Edition

12. The if...else Structure (continued)
Java Programming, Fifth Edition

13. Using Multiple Statements in an if or if...else Structure
Execute more than one statement
Use pair of curly braces
Place dependent statements within block
Crucial to place curly braces correctly
Any variable declared within block local to that block
Java Programming, Fifth Edition

14. Java Programming, Fifth Edition

15. Nesting if and if...else Statements
Nested if statements
Statements in which if structure is contained inside of another if structure
Use when two conditions must be met before some action is taken
Pay careful attention to placement of else clauses
else statements
Always associated with if on “first in-last out” basis
Java Programming, Fifth Edition

16. Nesting if and if...else Statements (continued)
Java Programming, Fifth Edition

17. Using Logical AND and OR Operators
Logical AND operator
Alternative to some nested if statements
Used between two Boolean expressions to determine whether both are true
Written as two ampersands (&&)
Include complete Boolean expression on each side
Both Boolean expressions that surround operator
Must be true before action in statement can occur
Java Programming, Fifth Edition

18. Using Logical AND and OR Operators (continued)
Java Programming, Fifth Edition

19. Using Logical AND and OR Operators (continued)
Logical OR operator
Action to occur when at least one of two conditions is true
Written as ||
Sometimes called pipes
Java Programming, Fifth Edition

20. Using Logical AND and OR Operators (continued)
Java Programming, Fifth Edition

21. Making Accurate and Efficient Decisions
Range check
Series of if statements that determine whether:
Value falls within specified range
Java programmers commonly place each else of subsequent if on same line
Within nested if...else
Most efficient to ask most likely question first
Avoid asking multiple questions
Java Programming, Fifth Edition

22. Making Accurate and Efficient Decisions (continued)
Java Programming, Fifth Edition

23. Using AND and OR Appropriately
Errors of beginning programmers
Using AND operator when they mean to use OR
Example: no payRate value can ever be both below 5.65 and over 60 at same time
if(payRate < 5.65 && payRate > 60)
System.out.println("Error in pay rate");
Use pipes “||” operator instead
Using single ampersand or pipe
To indicate logical AND or OR
Java Programming, Fifth Edition

24. Using the switch Statement
Alternative to series of nested if statements
Test single variable against series of exact integer or character values
Java Programming, Fifth Edition

25. Using the switch Statement (continued)
Switch structure keywords
switch
Starts structure
Followed by test expression
Enclosed in parentheses
case
Followed by one of the possible values for test expression and colon
Java Programming, Fifth Edition

26. Using the switch Statement (continued)
Switch structure keywords (continued)
break
Optionally terminates switch structure at end of each case
default
Used prior to any action if test variable does not match any case
Optional
Java Programming, Fifth Edition

27. Using the switch Statement (continued)
Java Programming, Fifth Edition

28. Using the switch Statement (continued)
break statements in switch structure
If break statement omitted
Program finds match for test variable
All statements within switch statement execute from that point forward
case statement
No need to write code for each case
Evaluate char variables
Ignore whether uppercase or lowercase
Java Programming, Fifth Edition

29. Using the switch Statement (continued)
Why use switch statements?
Convenient when several alternative courses of action depend on single integer or character variable
Use only when there are reasonable number of specific matching values to be tested
Java Programming, Fifth Edition

30. Using the NOT Operator NOT operator Statements with NOT operator
Written as exclamation point (!)
Negates result of any Boolean expression
When preceded by NOT operator
Any expression evaluates as:
true becomes false
false becomes true
Statements with NOT operator
Harder to read
Require double set of parentheses
Java Programming, Fifth Edition

31. Understanding Precedence
Combine as many AND or OR operators as needed
Operator’s precedence
How expression is evaluated
Order agrees with common algebraic usage
Arithmetic done first
Assignment done last
AND operator evaluated before OR operator
Statements in parentheses evaluated first
Java Programming, Fifth Edition

32. Understanding Precedence (continued)
Java Programming, Fifth Edition

33. Understanding Precedence (continued)
Two important conventions
Order in which operators are used
Always use parentheses
Change precedence
Or make your intentions clearer
Java Programming, Fifth Edition

34. Understanding Precedence (continued)
Java Programming, Fifth Edition