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Java Programming: Guided
Learning with Early Objects
Chapter 1
Basic Elements of Java
Objectives
• Become familiar with the basic components of a
Java program
• Explore primitive data types
• Discover how to use arithmetic operators
• Examine how a program evaluates arithmetic
expressions
• Explore how mixed expressions are evaluated
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Objectives (continued)
• Learn about type casting
• Become familiar with the String type
• Learn what an assignment statement is and
what it does
• Become familiar with the use of increment and
decrement operators
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Objectives (continued)
• Discover how to create a Java application
program
• Explore how to structure a program properly
• Learn how to avoid bugs by using consistent
and proper formatting
• Learn how to do a code walk-through
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A Java Program
• Basic unit of a Java program is a class
• Class: consists of one or more methods
• Method: a sequence of statements
– Objective is to accomplish something
• Braces mark beginning and end of class
• Execution always begins with main method
– Every application must have a main method
– Class can have at most one main method
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Basics of a Java Program
• Two types of Java programs:
– Applets
– Applications
• Syntax rules tell you which statements are
legal
• Semantic rules determine meaning of
instructions
• Programming language:
– Set of rules, symbols, special words used to
construct programs
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Comments
• Comments used to identify:
–
–
–
–
Program authors
Date when the program written or modified
Brief explanation of the program
Meaning of key statements
• Single-line comments begin with //
– Can be placed anywhere in the line
• Multiple-line comments inside /* and */
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Special Symbols
• Token: smallest individual unit of a program
• Java tokens are divided into special symbols,
reserved words, and identifiers
• Special symbols:
+ - * / , ; ? .
<= != == >=
• Also include blanks
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Reserved Words
• Reserved words also called keywords
• Examples of reserved words:
int, float, double, char, void,
public, static, throws, return
• Reserved words always lowercase
• Each word considered a single symbol
• Cannot be used for any other purpose
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Identifiers
• Names of things
– Variables, constants, methods, classes
– Predefined or user-defined
• Letters, digits, underscore, dollar sign
– May not begin with a digit
• Any length
• Predefined identifiers may be redefined by the
user
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White Spaces
• Include blanks, tabs, newline characters
• Separate special symbols, reserved words,
identifiers
• Nonprinted characters
• Format the program
– Make it readable
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Data Types
• Java programs manipulate data
• Java categorizes data into different types
• Certain operations performed only on certain
types of data
• Data type: set of values together with a set of
operations
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Primitive Data Types
• Fundamental data types in Java
• Integral
– Integers, characters
• Floating-point
– Decimal numbers
• Boolean
– Logical values: true or false
• Integral types:
– char, byte, short, int, long
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Table 1-2 Values and Memory Allocation for Integral Data Types
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int Data Type
• Examples of integers:
-6728, -67, 0, 78, 36782, +763
• Positive integers do not require a + sign in front
• No commas are used in an integer
– Commas only used to separate list items
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char Data Type
• 65536 values, numbered from 0 to 65535
• Represents single characters
– Letters, digits, special symbols
• Enclose character represented in single quotes
– Blank character written as ‘ ’
• Special symbols:
– Newline: ‘\n’
– Tab: ‘\t’
– Null: ‘\0’
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boolean Data Type
• Two values: true and false
– Also called logical values
• Primary purpose to manipulate logical
expression
• boolean, true, false are reserved words
• boolean data type allocated one bit in memory
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Floating-Point Data Types
• Recall scientific notation:
43872918 = 4.3872918 x 107
.0000265 = 2.65 x 10-5
• float
– Real numbers between -3.4E+38 and 3.4E+38
– Single precision
• double
– Real number between -1.7E+308 and 17E+308
– Double precision
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Literals (Constants)
• Values such as 23 and -67 are integer literals
– Also called integer constants or integers
• Values such as 12.34 and 25.60 are floatingpoint literals
– Also called floating-point constants or
floating-point numbers
• Values such as ‘a’ and ‘5’ are character
literals
– Also called character constants or characters
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Arithmetic Operators
and Operator Precedence
• Arithmetic operators:
–
–
–
–
–
Addition +
Subtraction (negation) –
Multiplication *
Division /
Mod (modulus or remainder) %
• Operands: constants and variables
• Unary operator: one operand
• Binary operator: two operands
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Order of Precedence
• Determines the order in which operations
performed
• Multiplication, division, modulus have higher
precedence than addition, subtraction
• Same level of precedence, operations
performed left to right
• Parentheses override precedence
• Associativity of arithmetic operators said to be
from left to right
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Expressions
• Integral expression: all numeric operands are
integers
– Yields an integral result
• Floating-point (decimal) expression: all
numeric operands are floating-point
– Yields a floating-point result
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Mixed Expressions
• Expression with operands of different data
types
• When evaluating operator
– If operands same type, operator evaluated
according to type of operand
– If operands of different types, integer treated as
floating point
• Entire expression evaluated according to
precedence rules
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Type Conversion (Casting)
• Implicit type coercion: value of one data type
automatically treated as another data type
• Cast operator (type conversion or type
casting): explicit type conversion
(dataTypeName) expression
• First expression evaluated, then treated as if
the value of type dataTypeName
• Floating-points cast as integer are truncated
• To cast char as int, use collating sequence
(int)‘A’ is 65
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class String
• String: sequence of zero or more characters
– Enclosed in double quotations
• Java class String contains operations to
process strings
• Null (empty) string: contains no characters
• Each character has a specific position
– First character is position 0
• Length of a string is the number of characters
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Strings and the Operator +
• Concatenation appends a string at the end of
another string
• Operator + concatenates:
– Two strings
– String and a numeric value
– String and a character
• Examples:
“Sunny” + “ Day” is “Sunny Day”
“Due = $” + 57.25 is “Due = $57.25”
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Named Constants, Variables,
and Assignment Statements
• Main objective of Java programs is to perform
calculations and manipulate data
• Data must be loaded into main memory before
it can be manipulated
• Storing data in memory is two-step process:
– Instruct computer to allocate named memory
space
– Include statement in the program to put data in
allocated memory
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Allocating Memory with Named
Constants and Variables
• Instruct the computer to allocate memory
– Name to use for each memory location
– Type of data to store in each location
• Computer system chooses the memory location
– Location may change from one execution to the
next
• Named constant: memory location whose
content does not change during execution
static final dataType IDENTIFIER = value;
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Allocating Memory with Named
Constants and Variables (continued)
• Reserved word static is optional
• Identifier for constants uppercase
– Words separated by underscores
• Variable: memory location whose content may
change during program execution
dataType identifier1, …, identifierN;
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Putting Data into Variables
• Two ways to put data into variables:
– Use an assignment statement
– Use an input (read) statement
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Assignment Statement
• Assignment statement:
variable = expression;
• Value of expression same data type as
variable
• Right side evaluated, assigned to left side
• Variable initialized the first time a value stored
• Assignment operator: =
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Table 1-2 Values of the Variables num1, num2, and num3
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Declaring and Initializing Variables
• Java does not automatically initialize variables
• Variables must be initialized before they are
used
int first;
first = 12;
• Can initialize variables when they are declared
int first = 12;
char ch = ‘ ’;
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Increment and Decrement Operators
• Incrementing a variable increases value by one
count = count + 1;
• Increment operator increases value by one
– Pre-increment: count++;
– Post-increment: ++count;
• Decrement operator decreases value by one
– Pre-decrement: count--;
– Post-decrement: --count;
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Creating a Java Application Program
• Basic unit of a Java program is a class
– Java application program a collection of classes
• Class a collection of methods, data members
• Method is a set of instructions to accomplish a
specific task
– Predefined methods
– User-defined methods
• One class in application must contain main
method
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Creating a Java Application Program
(continued)
• Syntax for a class:
public class ClassName
{
classMembers
}
• Syntax for main method:
public static void main (String[] args)
{
statement1
…
statementN
}
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Syntax, Semantics, and Errors
• Using proper structure makes program easier
to understand and modify
• Program that is syntactically correct but has no
structure is difficult to follow
• Every program must satisfy syntax rules
• Semantic rules give meaning to the program
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Syntax
• Syntax rules determine what is legal
• If program violates syntax rules, will not compile
– Compiler generates error message
• One syntax error may generate multiple
compiler errors
• Correct syntax errors in order in which compiler
lists them
• Compilers also provide hints
– Sometimes tell you the location and how to fix
the error
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Use of Semicolons, Braces,
and Commas
• Semicolon is the statement terminator
• Braces delimit the body of a class or body of a
method
• Commas separate items in a list
– Use commas to declare more than one variable
of a given data type
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Semantics
• Semantics: rules that give meaning to a
language
– Example: order-of-precedence rules
• Possible to eliminate syntax errors and still
have semantic errors
• Example:
2 + 3 * 5 substituted for
(2 + 3) * 5
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Form and Style
• Rules give Java a great degree of freedom
– Many ways to do the same task
• Use formatting to make program readable
– Programs should be indented and formatted
properly
– Align associated left and right braces
– Indent for a new set of braces
– Blank lines to separate portions of a program
– Declare one variable per line
– Space before and after operator
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Avoiding Bugs:
Consistent, Proper Formatting
• Consistent, proper formatting makes it easier to
debug and maintain programs
• Consistent use of white space
• Consistent and predictable use of upper and
lowercase
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Debugging: Code Walk-Throughs
• Syntactically correct programs may produce
incorrect results or crash
• Programmers walk through their own programs
• Can be advantageous to invite another
programmer to review the code
– Must format and comment the code first
– Must explain the code to the other person
• Presentation to larger group is also a walkthrough
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Summary
• Basic unit of a Java program is a class
• Class consists of one or more methods
• Method is a sequence of statements to
accomplish a specific task
• Execution always begins with main method
• Every application must have a main method
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Summary (continued)
• Syntax rules tell you which statements are legal
• Semantic rules determine meaning of
instructions
• Java tokens are divided into special symbols,
reserved words, and identifiers
• Data type: set of values together with a set of
operations
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Summary (continued)
• Fundamental data types in Java:
– Integral
– Floating-point
– Boolean
• Integral types:
– char, byte, short, int, long
• Floating-point types:
– float, double
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Summary (continued)
• Multiplication, division, modulus have higher
precedence than addition, subtraction
– Operations performed left to right
• Implicit type coercion: value of one data type
automatically treated as another data type
• Explicit type casting: cast operator
(dataTypeName) expression
• String: sequence of zero or more characters
– Enclosed in double quotations
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Summary (continued)
• Storing data in memory is two-step process:
– Instruct computer to allocate named memory
space
– Include statement in the program to put data in
allocated memory
• Instruct the computer to allocate memory
– Name to use for each memory location
– Type of data to store in each location
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Summary (continued)
• Named constant: memory location whose
content does not change during execution
• Variable: memory location whose content may
change during program execution
• Increment operator increases value by one
• Decrement operator decreases value by one
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Summary (continued)
• Using proper structure makes program easier
to understand and modify
• Correct syntax errors in order in which compiler
lists them
• Possible to eliminate syntax errors and still
have semantic errors
• Use formatting to make program readable
• Code walk-throughs help debugging
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