OOP Using Java Ch2 all about oop .pptx

Object Oriented
Programming Using Java
Dr. Akmal
1

Chapter 2
Introduction to
Java Applications;
Input/Output and Operators
Java™ How to Program, 10/e
© Copyright 1992-2015 by Pearson
Education, Inc. All Rights Reserved.
2

© Copyright 1992-2015 by Pearson Education, Inc. All Rights
Reserved.
3

2.3 Modifying Your First Java Program
• Class Welcome2, shown in Fig. 2.3, uses two statements to produce
the same output as that shown in Fig. 2.1.
• New and key features in each code listing are highlighted.
• System.out’s method print displays a string.
• Unlike println, print does not position the output cursor at the
beginning of the next line in the command window.
 The next character the program displays will appear immediately after the last
character that print displays.
Reserved.
4

Reserved.
5

2.3 Modifying Your First Java Program (Cont.)
• Newline characters indicate to System.out’s print and println
methods when to position the output cursor at the beginning of the next line in
the command window.
• Newline characters are whitespace characters.
• The backslash () is called an escape character.
 Indicates a “special character”
• Backslash is combined with the next character to form an escape sequence—
n represents the newline character.
• Complete list of escape sequences
http://docs.oracle.com/javase/specs/jls/se7/html/
jls-3.html#jls-3.10.6.
Reserved.
6

Reserved.
7

Reserved.
8

2.4 Displaying Text with printf
• System.out.printf method
 f means “formatted”
 displays formatted data
• Multiple method arguments are placed in a comma-separated list.
• Calling a method is also referred to as invoking a method.
• Java allows large statements to be split over many lines.
 Cannot split a statement in the middle of an identifier or string.
• Method printf’s first argument is a format string
 May consist of fixed text and format specifiers.
 Fixed text is output as it would be by print or println.
 Each format specifier is a placeholder for a value and specifies the type of
data to output.
• Format specifiers begin with a percent sign (%) and are followed by a
character that represents the data type.
• Format specifier %s is a placeholder for a string.
Reserved.
9

Reserved.
10

2.5 Another Application: Adding Integers
• Integers
 Whole numbers, like –22, 7, 0 and 1024)
• Programs remember numbers and other data in the computer’s
memory and access that data through program elements called
variables.
• The program of Fig. 2.7 demonstrates these concepts.
Reserved.
11

Reserved.
12

Reserved.
13

2.5.1 import Declarations
• Helps the compiler locate a class that is used in this program.
• Rich set of predefined classes that you can reuse rather than
“reinventing the wheel.”
• Classes are grouped into packages—named groups of related
classes—and are collectively referred to as the Java class library, or
the Java Application Programming Interface (Java API).
• You use import declarations to identify the predefined classes used
in a Java program.
Reserved.
14

2.5.3 Declaring and Creating a Scanner to
Obtain User Input from the Keyboard
• Variable declaration statement
Scanner input = new Scanner( System.in );
 Specifies the name (input) and type (Scanner) of a variable that is used in this
program.
• Variable
 A location in the computer’s memory where a value can be stored for use later in a
program.
 Must be declared with a name and a type before they can be used.
 A variable’s name enables the program to access the value of the variable in memory.
 The name can be any valid identifier.
 A variable’s type specifies what kind of information is stored at that location in memory.
Reserved.
15

2.5 Another Application: Adding Integers (Cont.)
• Scanner
 Enables a program to read data for use in a program.
 Data can come from many sources, such as the user at the keyboard or a file on disk.
 Before using a Scanner, you must create it and specify the source of the data.
• The equals sign (=) in a declaration indicates that the variable should be initialized
(i.e., prepared for use in the program) with the result of the expression to the right of
the equals sign.
• The new keyword creates an object.
• Standard input object, System.in, enables applications to read bytes of data typed
by the user.
• Scanner object translates these bytes into types that can be used in a program.
Reserved.
16

2.5.4 Declaring Variables to Store Integers
• Variable declaration statements
int number1; // first number to add
int number2; // second number to add
int sum; // sum of number1 and number2
declare that variables number1, number2 and sum hold data of type int
 They can hold integer.
 Range of values for an int is –2,147,483,648 to +2,147,483,647.
 The int values you use in a program may not contain commas.
• Several variables of the same type may be declared in one declaration with the
variable names separated by commas.
Reserved.
17

2.5.5 Prompting the User for Input
• Prompt
 Output statement that directs the user to take a specific action.
• Class System
 Part of package java.lang.
 Class System is not imported with an import declaration at the beginning
of the program.
Reserved.
18

2.5.6 Obtaining an int as Input from the User
• Scanner method nextInt
number1 = input.nextInt(); // read first number from
user
 Obtains an integer from the user at the keyboard.
 Program waits for the user to type the number and press the
Enter key to submit the number to the program.
• The result of the call to method nextInt is placed in
variable number1 by using the assignment operator,
=.
 “number1 gets the value of input.nextInt().”
 Operator = is called a binary operator—it has two operands.
 Everything to the right of the assignment operator, =, is
always evaluated before the assignment is performed.
Reserved.
19

2.5 Another Application: Adding Integers (Cont.)
• Arithmetic
sum = number1 + number2; // add numbers then store total
in sum
 Assignment statement that calculates the sum of the variables
number1 and number2 then assigns the result to variable
sum by using the assignment operator, =.
 “sum gets the value of number1 + number2.”
 Portions of statements that contain calculations are called
expressions.
 An expression is any portion of a statement that has a value
associated with it.
Reserved.
20

2.5.9 Displaying the Result of the Calculation
• Integer formatted output
System.out.printf( "Sum is %d%n", sum );
 Format specifier %d is a placeholder for an int value
 The letter d stands for “decimal integer.”
Reserved.
21

2.7 Arithmetic
• Arithmetic operators are summarized in Fig. 2.11.
• The asterisk (*) indicates multiplication
• The percent sign (%) is the remainder operator
• The arithmetic operators are binary operators because they each
operate on two operands.
• Integer division yields an integer quotient.
 Any fractional part in integer division is simply truncated (i.e., discarded)—no
rounding occurs.
• The remainder operator, %, yields the remainder after division.
Reserved.
22

Reserved.
23

2.7 Arithmetic (Cont.)
• Arithmetic expressions in Java must be written in straight-line form to
facilitate entering programs into the computer.
• Expressions such as “a divided by b” must be written as a / b, so that
all constants, variables and operators appear in a straight line.
• Parentheses are used to group terms in expressions in the same manner
as in algebraic expressions.
• If an expression contains nested parentheses, the expression in the
innermost set of parentheses is evaluated first.
Reserved.
24

• Rules of operator precedence
 Multiplication, division and remainder operations are applied first.
 If an expression contains several such operations, they are applied from left to right.
 Multiplication, division and remainder operators have the same level of precedence.
 Addition and subtraction operations are applied next.
 If an expression contains several such operations, the operators are applied from left to right.
 Addition and subtraction operators have the same level of precedence.
• When we say that operators are applied from left to right, we are referring to their
associativity.
• Some operators associate from right to left.
• Complete precedence chart is included in Appendix A.
Reserved.
25

Reserved.
26

Reserved.
27

• As in algebra, it’s acceptable to place redundant parentheses
(unnecessary parentheses) in an ex-pression to make the expression
clearer.
Reserved.
28

2.8 Decision Making: Equality and Relational
Operators
• Condition
 An expression that can be true or false.
• if selection statement
 Allows a program to make a decision based on a condition’s value.
• Equality operators (== and !=)
• Relational operators (>, <, >= and <=)
• Both equality operators have the same level of precedence, which is lower than
that of the relational operators.
• The equality operators associate from left to right.
• The relational operators all have the same level of precedence and also
associate from left to right.
Reserved.
29

Reserved.
30

Reserved.
31

Reserved.
32

Reserved.
33

2.8 Decision Making: Equality and Relational
Operators (Cont.)
• An if statement always begins with keyword if, followed by a
condition in parentheses.
 Expects one statement in its body, but may contain multiple statements if they
are enclosed in a set of braces ({}).
 The indentation of the body statement is not required, but it improves the
program’s readability by emphasizing that statements are part of the body.
• Note that there is no semicolon (;) at the end of the first line of each
if statement.
 Such a semicolon would result in a logic error at execution time.
 Treated as the empty statement—semicolon by itself.
Reserved.
34

Reserved.
35

OOP Using Java Ch2 all about oop .pptx

More Related Content

Similar to OOP Using Java Ch2 all about oop .pptx (20)

Recently uploaded (20)

OOP Using Java Ch2 all about oop .pptx