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Introduction to Java
Appendix A
Chapter Objectives
• To understand the essentials of object-oriented
programming in Java
• To learn about the primitive data types of Java
• To understand how to use the control structures of Java
• To learn how to use predefined classes such as Math,
JOptionPane, String, StringBuffer, and StringTokenizer
• To learn how to write and document your own Java
classes
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Chapter Objectives (continued)
• To understand how to use arrays in Java
• To learn how to perform I/O in Java using simple dialog
windows
• To learn how to perform I/O in Java using streams
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The Java Environment and Classes
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Platform independent
Object oriented
Can be embedded in Web pages
JVM is a software computer that runs inside an actual
computer
• Java code is first translated into Java byte code
instructions which are then interpreted by the JVM
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Compiling and Executing a Java Program
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Classes and Objects
• The class is the fundamental programming unit
• Every program is written as a collection of classes
• Class definitions are stored in separate files with the
extension .java and the file name must be the same as
the class name
• A class is a named description for a group of entities
• A class is a general description of a group of entities that
all have the same characteristics; each entity is an object
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The Java API
• Java consists of small core language augmented by an
extensive collection of packages
• Each package contains a collection of related Java
classes, such as:
• Swing
• AWT
• util
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The import Statement and the Main Method
• Import statement tells the compiler to make the names
defined in a specified package accessible to the code file
• The main function identifies where the JVM begins
execution of an application program
• Keywords “public static void” tell the compiler that main
is accessible outside of the class, is static, and does not
return a value
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Primitive Data Types and Reference
Variables
• Java distinguishes two kinds of entities
• Primitive types
• Objects
• Primitive type data is stored in primitive type variables
• Objects are associated with reference variables which
store an object’s address
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Primitive Data Types
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Represent numbers, characters, and Boolean values
Integers: byte, short, int, and long
Real numbers: float and double
Characters: char
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Primitive Data Types (continued)
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Operators
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Type Compatibility and Conversion
• Widening conversion: operations involving mixed-type
operands, the numeric type of the smaller range is
converted to the numeric type of the larger range
• In an assignment operation, a numeric type of smaller
range can be assigned to a numeric type of larger range
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Referencing and Creating Objects
• You can declare reference variables that reference
objects of specified types
• Two reference variables can reference the same object
• The new operator creates an instance of a class
• A constructor executes when a new object is created
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Java Control Statements
• A group of statements executed in sequence is written
as a compound statement delimited by braces
• The statements execute in the order in which they are
listed
• Control Statements alter the sequential flow of execution
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Java Control Statements (continued)
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Java Control Statements (continued)
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Methods
• Programmers use methods to define a group of
statements that perform a particular operation
• The modifier static indicates a static or class method
• A method that is not static is an instance method
• All method arguments are call-by-value
• If the argument is a primitive type, its value is passed to
the method
• The method can’t modify the argument value and
have the modification remain after return from the
method
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Methods (continued)
• If the argument is of a class type, the value of the
reference variable is passed, not the value of the object
itself
• Reference variables point to the object and any
modification to the object will remain after return from the
method
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The Class Math
• Provides a collection of methods that are useful for
performing common mathematical operations
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Escape Sequences
• An escape sequence is a sequence of two characters
beginning with the character \
• Represents characters or symbols that have a special
meaning in Java
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The String Class
• String class defines a data type that is used to store a
sequence of characters
• You cannot modify a String object
• If you attempt to do so, Java will create a new object
that contains the modified character sequence
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Comparing Objects
• You can’t use the relational operators or equality
operators to compare the values stored in strings or
other objects
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The StringBuffer Class
• Stores character sequences
• Unlike a String object, the contents of a StringBuffer
object can be changed
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StringTokenizer Class
• We often need to process individual pieces, or tokens, in
a string
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Wrapper Classes for Primitive Types
• Sometimes we need to process primitive-type data as
objects
• Java provides a set of classes called wrapper classes
whose objects contain primitive-type values: Float,
Double, Integer, Boolean, Character, etc.
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Defining Your Own Classes
• Unified Modeling Language is often used to represent a
class
• Standard means of documenting class relationships
widely used in industry
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Defining Your Own Classes (continued)
• The modifier private sets the visibility of each variable or
constant to private visibility
• These data fields can be accessed only within the
class definition
• Only class members with public visibility can be
accessed outside of the class
• Constructors initialize the data fields within a class
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Arrays
• In Java, an array is also an object
• The elements are indexes and are referenced using a
subscripted variable of the form arrayname[subscript]
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Input/Output using Class JOptionPane
• Prior to Java 2, it was fairly difficult to perform
input/output operations
• Java 2 provides JOptionPane which facilitates the
display of dialog windows for input and message
windows for output
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Input/Output using Class JOptionPane
(continued)
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Converting Numeric Strings to Numbers
• A dialog window always returns a reference to a string
• Therefore, a conversion is required
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Input/Output using Streams
• An input stream is a sequence of characters
representing program data
• An output stream is a sequence of characters
representing program output
• The console keyboard stream is System.in
• The console window is associated with System.out
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Chapter Review
• A Java program is a collection of classes
• JVM enables a Java program written for one machine to
execute on any other machine that has a JVM
• Java defines a set of primitive data types that are used
to represent numbers, characters, and Boolean data
• The control structures of Java are similar to those found
in other languages
• The Java String and StringBuffer classes are used to
reference objects that store character strings
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Chapter Review (continued)
• Be sure to use methods such as equals and compareTo
to compare the contents of two String objects
• You can declare your own Java classes and create
objects of these classes using the new operator
• A class has data fields and instance methods
• Array variables can reference array objects
• Class JOptionPane can be used to display dialog
windows for data entry and message windows for output
• The stream classes in package java.io read strings from
the console and display strings to the console
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