201707 CSE110 Lecture 08

CSE110
Principles of Programming
with Java
Lecture 08:
Nested if-else Statements
Javier Gonzalez-Sanchez
javiergs@asu.edu
javiergs.engineering.asu.edu
Office Hours: By appointment

Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 2
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

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!");
}
}
}

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!");
}

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”);

Example

Full set of Operators
• Arithmetic
• Relational
• Logical (Boolean)

Comparing Characters
• We can use the relational operators on character
data
• The results are based on the Unicode character set
• The following condition is true because the
character + comes before the character J in the
Unicode character set:
if ('+' < 'J') System.out.println ("+ is less than J");
• The uppercase alphabet (A-Z) followed by the
lowercase alphabet (a-z) appear in alphabetical
order in the Unicode character set

Comparing Characters
• Comparing characters is based on a character set,
it is called a lexicographic ordering
• It uses Unicode of each character.
• Therefore it distinguishes upper and lower cases. i.e.,
“Apple” and “apple” are considered to be different.
(unicode for ‘a’ is 97, and unicode for ‘A’ is 65)

Comparing Strings
• Remember that a character string in Java is not a
primitive data type.
• We cannot use the relational operators to compare
strings
• Do NOT do this
String str1 = "apple";
String str2 = "banana";
if (str1 == str2){//we are not supposed to do this
}

Comparing Strings
//do NOT do this
if (str1 == str2){
}
// Instead we need to do:
if (str1.equals(str2)){
}

Comparing Strings
• The following does not also compare two strings:
//do NOT do this
if (str1 < str2){
}
// Instead we need to do:
if (str1.compareTo(str2)){
}

Example
int result = str1.compareTo(str2);
if (result < 0) {
//if str1 is smaller than str2
} else if (result > 0){
//if str1 is larger than str2
} else if (result == 0)
//if str1 is identical to str2
}

Comparing Strings
• Comparing strings is based on a character set, it is
called a lexicographic ordering
• It uses Unicode of each character in strings.
• Also, short strings come before longer strings with
the same prefix (lexicographically)
Therefore "book" comes before "bookcase"

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 08

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