201707 CSE110 Lecture 07

CSE110
Principles of Programming
with Java
Lecture 07:
Conditional Statements
Javier Gonzalez-Sanchez
javiergs@asu.edu
javiergs.engineering.asu.edu
Office Hours: By appointment

Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 2
Flow of Control
Unless specified otherwise, the order of statement
execution through a method is linear: one statement after
the other in sequence (top down order).
public static void main (String [] args) {
System.out.println(“one”);
System.out.println(“two”);
System.out.println(“three”);
}
The order of statement execution is called the flow of control

Flow of Control
Some programming statements modify that order
(flow of control), allowing us to:
• decide whether or not to execute a particular
statement, or
• perform a statement over and over, repetitively
These decisions are based on a boolean expression
(also called a condition) that evaluates to true or
false.

Topics
class
global
variables
methods statements
instructions
local
variables
conditional
Statements
loop
Statements

Conditional Statements
• A conditional statement lets us choose which
statement will be executed next
• Java's conditional statements are
o the if statement
o the if-else statement
o the switch statement
o the operator ?

if statement
• The if statement has the following syntax:

Example
int MAX = 5;
int sum = 30;
int delta = 0;
if (sum > MAX) {
delta = sum - MAX;
}
System.out.println("The delta is " + delta);

Flow Chart of an if statement

Boolean expressions
A condition uses relational operators, which all return
boolean results:
== equal to
!= not equal to
< less than
> greater than
<= less than or equal to
>= greater than or equal to
Note the difference between the equality operator
(==) and the assignment operator (=)

if-else statement
An else clause can be added to an if statement to
make an if-else statement
if ( condition ) {
statement1;
} else {
statement2;
}
• If the condition is true, statement1 is executed; if the
condition is false, statement2 is executed
• One or the other will be executed, but not both

Flow chart of an if-else statement

Nested if Statements
• The statement executed as a result of an if
statement or else clause could be another if
statement
• These are called nested if statements
• An else clause is matched to the last unmatched if
(no matter what the indentation implies)
• Braces can be used to specify the if statement to
which an else clause belongs

if-else if-else
You can also have multiple conditions to be verified:
if (temp > 100) {
System.out.println("It is hot!");
} else if (temp > 80) {
System.out.println("It is warm");
} else if (temp > 50) {
System.out.println("It is chilly");
} else {
System.out.println("It is cold!");
}

if-else if-else
The code from the previous page is equivalent to:
if (temp > 100) {
System.out.println("It is hot!");
else {
if (temp > 80) {
System.out.println("It is warm");
} else {
if (temp > 50){
System.out.println("It is chilly");
} else {
System.out.println("It is cold!");
}
}
}

Block Statements
• Several statements are grouped together into a
block statement
• A block is delimited by braces: {...}
• For example, in an if-else statement, the if portion,
or the else portion, or both, could be block
statements
• There is no need to use braces if there is only one
statement or one set of “if-else” within the outer “if”
statement

Block Statements

Logical Operators
• Boolean expressions can use the following logical
operators:
! Logical NOT
&& Logical AND
|| Logical OR
• They all take boolean operands and produce boolean
results
• Logical NOT is a unary operator (it operates on one
operand)
• Logical AND and logical OR are binary operators (each
operates on two operands)

Logical NOT
• The logical NOT operation is also called logical
negation or logical complement
• If some boolean condition a is true, then !a is false; if
a is false, then !a is true
• Logical expressions can be shown using truth tables

Logical AND and Logical OR
• The logical AND expression
a && b
is true if both a and b are true, and false otherwise
• The logical OR expression
a || b
is true if a or b or both are true, and false otherwise

Logical AND and Logical OR
• Since && and || each have two operands, there
are four possible combinations of conditions a and
b

Logical Operators
Conditions can use logical operators to form complex
expressions
if (total < MAX+5 && !found)
System.out.println ("Processing...");
Logical operators have precedence relationships among
themselves and with other operators
• The relational or arithmetic operators have higher
precedence than logical AND and logical OR
• logical NOT has higher precedence than logical AND.
Logical AND has higher precedence than logical OR

Example
int examGrade = 90;
int assignmentGrade = 80;
int quizGrade = 85;
if (examGrade > 85 && assignmentGrade > 85)
System.out.println(“Well done!”);
else if (quizGrade < 70 || assignmentGrade < 85)
System.out.println(“Houston, we have a problem”);

Reference
Textbook – Section 3.1, 3.2, and 3.3

CSE110 - Principles of Programming
Javier Gonzalez-Sanchez
javiergs@asu.edu
Summer 2017
Disclaimer. These slides can only be used as study material for the class CSE110 at ASU. They cannot be distributed or used for another purpose.

201707 CSE110 Lecture 07

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