CIS 265: Data Structure and
Algorithms
Lecture 01
Java Programming Review
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Outline
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Introduction to computers, programs, and Java
Elementary programming
Selection
Loops
Methods
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Outline
•
•
•
•
•
Introduction to computers, programs, and Java
Elementary programming
Selection
Loops
Methods
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Introduction to programs
• Writing a program involves designing
algorithms and translating algorithms into code.
• An algorithm describes how a problem is solved
in terms of the actions to be executed and the
order of their execution.
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Executing a Java Program
• You can use any text
editor or IDE to create
and edit a Java sourcecode file.
• The source file must end
with the extension .java
and must have exactly
the same name as the
public class name.
• You must first install
and configure JDK
before compiling and
running programs
Creating java source file
The execution process
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Development Process
The Java program development process
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Outline
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Introduction to computers, programs, and Java
Elementary programming
Selection
Loops
Methods
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Writing Simple Programs
Example: Write a program to calculate the area of
a circle.
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Input/output
• Use scanner class to create input object
• Use methods of a scanner objects: nextDouble()
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Variables
• They represent data of a certain type.
• They are basic structures.
• Examples:
Numeric data types
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Operations & Expressions
• Operations:
• Java expressions
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Example
• Write a program that obtains minutes and
remaining seconds from an amount of time in
seconds.
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Outline
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Introduction to computers, programs, and Java
Elementary programming
Selection
Loops
Methods
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Boolean Data Type
• Example:
• Java provides six comparison operators:
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if statements
• One way if statement
• The boolean expression is enclosed in
parenthesis.
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Block braces
• The block braces can be omitted if they enclose a
single statement.
• Example:
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Two Way if Statements
• Example:
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Nested if Statements
• Example:
• Problem: Compute Body Mass Index
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Body mass index program
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Logical Operators
• Sometimes, whether a statement is executed is
determined by a combination of several
conditions. You can use logical operators to
combine these conditions.
• How the truth table will look like?
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Switch Statements
• The if statement usually makes selection based
on a single true or false condition. Switch
statement can work based on different
conditions.
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Caution
• Do not forget to use a break statement when
one is needed. Once a case is matched, the
statements starting from the matched case are
executed until a break statement or the end of
the switch statement is reached.
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Formatting Console Output
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Conditional Expressions
• Example:
• Alternative way:
• Example:
• Find out a number is even or odd:
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Outline
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Introduction to computers, programs, and Java
Elementary programming
Selection
Loops
Methods
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Loops
• Suppose you need to print a string a hundred
times.
• Using a loop statement, you simply tell the
computer to print a string a hundred times
without having to code the print statement a
hundred times, as follows:
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The while loop
• Example:
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Examples
• Write a program to receive 100 numbers and
calculate their average.
• Write a program to receive 100 numbers and
count even and odd numbers.
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The do-while Loop
• The loop body is executed first. Then the loopcontinuation-condition is evaluated. If the
evaluation is true, the loop body is executed
again; if it is false, the do-while loop
terminates.
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Example
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The For loop
• It is a quite common loop:
• A for loop can be used to simplify the proceeding
loop:
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Which loop to use?
• The while loop and for loop are called pretest loops
because the continuation condition is checked
before the loop body is executed.
• The do-while loop is called a posttest loop because
the condition is checked after the loop body is
executed.
• The three forms of loop statements, while, dowhile, and for, are expressively equivalent; that is,
you can write a loop in any of these three forms.
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Outline
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•
•
•
•
Introduction to computers, programs, and Java
Elementary programming
Selection
Loops
Methods
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Why methods?
• Code looks similar except that starting and
ending integers are different. Wouldn’t it be nice
if we could write the common code once and
reuse it without rewriting it?
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Defining a method
• The syntax is as follows:
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Calling a method
• In creating a method,
you define what the
method is to do. To use
a method, you have to
call or invoke it.
• If the method returns a
value, a call to the
method is usually
treated as a value. For
example:
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Call Stacks
• Each time a method is invoked, the system
stores parameters and variables in an area of
memory known as a stack, which stores
elements in last-in, first-out fashion.
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Passing parameters by values
• When calling a method, you need to provide arguments,
which must be given in the same order as their
respective parameters in the method signature.
• When you invoke a method with a parameter, the value
of the argument is passed to the parameter. This is
referred to as pass-by-value.
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Swap two values
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Look at stack
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The scope of variables
• The scope of a variable is the part of the program where
the variable can be referenced. A variable defined inside
a method is referred to as a local variable.
• The scope of a local variable starts from its declaration
and continues to the end of the block that contains the
variable.