presentation of java fundamental
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This document provides an overview of Chapter 2 from a Java fundamentals textbook. It covers several topics: 1) A payroll program example to demonstrate object-oriented design principles and programming concepts. 2) Java primitive data types, variables, literals, and constants. It describes how data is represented in memory. 3) Basic program features like comments, classes, importing packages, and using methods. 4) The Java Application Programming Interface (API) documentation and how to use it to find needed classes. 5) An example program that creates a graphical user interface (GUI) to greet a user by name.
![Types
void
denotes the absence of any type
String [ ]
in general, a sequence of characters
Keyboard, Screen
associated to the Input and Output (I/O) devices
normally used
double
associated with real (numbers with fractions)
values](https://image.slidesharecdn.com/chap02-190420181032/85/presentation-of-java-fundamental-12-320.jpg)
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presentation of java fundamental
- 2. Chapter Contents Chapter Objectives 2.1 Example: A Payroll Program 2.2 Types, Variables, and Constants Part of the Picture: Data Representation 2.3 Some Basic Program Features 2.4 Java Documentation 2.5 Introduction to GUIs: A GUI Greeter
- 3. Chapter Objectives Observe Java primitive types and their literals Explain Java syntax rules Contrast primitive types and reference types Study variables and constants Investigate internal representation of primitive types
- 4. Chapter Objectives Observe the structure and declaration of classes Discover need for import statements Note how to use methods Study Java API organization Look at designing and building simple GUI applications
- 5. 2.1 Example: A Payroll Program Computerize the calculation of employee wages. Employees are paid a fixed hourly rate They can work any number of hours No overtime is paid Use object-oriented design Describe behavior Identify objects Identify operations Organize objects & operations in an algorithm
- 6. Behavior Display on the screen a prompt for … hours worked hourly rate Enter values via keyboard Compute wages Display calculations with descriptive label
- 7. Objects Description of Object Type Kind Name the program ?? ?? ?? screen Screen variable theScreen prompt for hrs & rate String constant none number hrs worked double variable hoursWorked hourly pay rate double variable hourlyRate keyboard Keyboard variable theKeyboard wages variable
- 8. Operations Display strings (prompts) on screen Read numbers for hours and rate (restrict to non negatives) Compute wages Display real value (wages) and a string on screen
- 9. Algorithm 1. Construct theScreen and theKeyboard objects 2. Ask theScreen to display prompt for hours 3. Ask theKeyboard to read value and store in hoursWorked 4. Ask theScreen to display prompt for rate 5. Ask theKeyboard to read value and store in hourlyRate 6. Compute wages = hoursWorked x hourlyRate 7. Ask theScreen to display wages and descriptive label
- 10. Coding, Testing, Maintenance Note Figure 2.1 Code Sample runs Maintenance Enhance to include overtime wages Display output using $999.99 style format Note revision Figure 2.2
- 11. 2.2 Types, Variables, and Constants Types of objects must be declared before they are used Declaration of variables requires a certain syntax In declaration, the name of a variable is associated with a type
- 12. Types void denotes the absence of any type String [ ] in general, a sequence of characters Keyboard, Screen associated to the Input and Output (I/O) devices normally used double associated with real (numbers with fractions) values
- 13. Primitive Types byte, short, int, and long for integer values of various sizes float and double for real (rational) values of differing accuracy boolean for logical (true/false) values char for individual characters
- 14. Reference Types Built of other types Example: String, Screen, Keyboard Also considered “class types” Reference types begin with uppercase letter not known to Java compiler, must be explained Contrast primitive types begin with lower case letter are known to Java compiler
- 15. Literals – Examples Integers 4, 19, -5, 0, 1000 Doubles 3.14, 0.0, -16.123 Strings “Hi Mom” “Enter the number : “ Character 'A' 'X' '9' '$' 'n' Boolean true, false
- 16. Identifiers Names given to variables, objects, methods Must not be a Java keyword See Appendix B for list of keywords May begin with a letter or the underline character _ Followed by any number of characters, digits, or _ (note, no blanks) Identifiers should be well chosen use complete words (even phrases) this helps program documentation
- 17. Conventions for Identifiers Classes Names given in lowercase except for first letter of each word in the name Variables Same as classes, except first letter is lowercase Constants All caps with _ between words Methods like variable names but followed by parentheses
- 18. Declaration Statements Purpose is to provide compiler with meaning of an identifier Accomplished in declaration statement Some declarations (classes and methods) are provided and must be imported import ann.easyio.*; Variables to store values must be declared they can be initialized at time of declaration initialized with a literal or even with keyboard input if not explicitly initialized, the default initial value is zero
- 19. Values Held by Variables Primitive-type variables store a value of the specified type (int, double) Reference-type variables store an address of memory location where value is stored thought of as a handle for the object that actually stores the values
- 20. Variable Declaration Syntax Syntax: type variable_name; or type variable_name = expression; Note type must be known to the compiler variable_name must be a valid identifier expression is evaluated and assigned to variable_name location In the first form, a default value is given (0, false, or null, depending on type)
- 21. Constants Value of object cannot be changed for oft used math values such as PI for values which will not change for a given program improve readability of program facilitate program maintenance Declaration syntax: final type CONSTANT_NAME = expression; final is a Java keyword, makes a constant type must be known by compiler CONSTANT_NAME must be valid identifier expression evaluated should be placed at beginning of class or method
- 22. Part of the Picture: Data Representation How literals of the primitive types are represented and stored in memory.
- 23. Representing Integers Binary digits used to represent base 10 numbers 58 ten = 111010two The 1s and 0s are stored as binary digits in specified number of bits (32 shown in text) Negative numbers often stored in "two's complement" representation All opposite values, switch 1s for 0s and 0s for 1s Leading bit specifies the sign (0 for +, 1 for -) If a number is too large for the number of bits allocated, the condition is overflow
- 24. Representing Reals Consider 22.625ten = 10110.101two = 1.0110101two x 24 The 1.0110101 is stored as the "mantissa" The 4 is stored as the exponent or "characteristic" IEEE format Leftmost bit is sign for mantissa 8 bits for exponent Rightmost 23 bits store mantissa Problems include Overflow – number too large for exponent Underflow – number too small for exponent Roundoff error – conversion between decimal & binary
- 25. Representing Characters A numeric code is assigned to each symbol to be represented ASCII uses 8 bits Very common for programming languages Limited to 128 characters Unicode uses 16 bits newer, used by Java Allows 65,536 different symbols
- 26. Representing Booleans Only two possible values true and false Only need two possible numbers, 0 and 1 Single bit is all that is needed
- 27. 2.3 Some Basic Program Features Comments and documentation Classes Importing packages Using Methods
- 28. Comments and Opening Documentation Opening documentation should include: description of what program does input needed, resulting output special techniques, algorithms used instructions for use of program Name of programmer, date, modification history Opening documentation is multiline between /* */ character pairs Inline comments following // double slashes Comments ignored by compiler
- 29. Classes Classes built for real world objects that cannot be represented using available types A class is an "extension" of Java Definition of class: "a group or category of things that have a set of attributes in common." In programming: a pattern, blueprint, or template for modeling real world objects which have similar attributes
- 30. Class Declaration Syntax: class className extends existingClassName { // Attributes (variables & constants) // and behaviors (methods) } Where className is the name of a new reference type existingClassName is any class name known to the compiler { and } mark the boundaries of the declaration
- 31. Purpose of Class Declaration Creates a new type that the compiler can use to create objects This new type inherits all attributes and behaviors of existingClassName Note: Object is often used for existingClassName in this case the extends object may be omitted
- 32. Importing Packages Related classes grouped together into a container called a "package" program specifies where to find a desired class Fully-qualified name package_name1.ClassName or package_name1.package_name2.ClassName By using the import package_name1 the prefixes using the dot notation can be omitted Syntax import package_name.* ; or import package_name.ClassName; where ClassName is any class stored with package_name
- 33. Using Methods Call, invoke, or send a message to the method of an existing object theScreen.print(" … "); theScreen is the object print ( ) is the method being called Syntax of the call name of the object the dot . the name of the method any required parameters or arguments
- 34. Value Returning Methods Some methods return a value Programmer must also do something with the value to be returned assign the value to a variable variable_name = objectName.methodName(arguments); send the value to another method as the parameter
- 35. 2.4 Java Documentation – API Note the sample programs so far … For several tasks, we found a Java method to solve it Other times the programmer writes the class and methods required Java designers have provided over 1600 classes Called the Java Application Programmer's Interface or API Each class provides variety of useful methods Classes grouped into packages
- 36. API Documentation Finding needed package or class Hypertext-based documentation system, accessible on World Wide Web First page of web site has 3 frames Alphabetical list of packages Alphabetical list of classes A "main" frame that initially lists the Java packages
- 37. Web Based Documentation Clicking on the name of the package in the "main" frame produces a list of the classes in that package Click on name of a class displays information about that class List of fields (variables, constants) List of methods for the class Click on a method for a detailed description of the methods This is an important reference source and you should learn to use it effectively
- 38. 2.5 Introduction to GUIs: A GUI Greeter Problem Scenario Write a program with graphical user interface that displays a window with prompt for name box to enter name OK and Cancel buttons User enters name, clicks OK Second window gives greeting, uses name, displays a button for terminating program
- 39. Objects Description of Problem's Objects Type Kind Name the program GUIGreeter window for prompt input- dialog prompt for user's name String constant window to display message
- 40. Operations Display a window containing a prompt and a text box Read a String from the window's text box Hide the window Display second window with personalized greeting Terminate program
- 41. Coding in Java Note source code in Figure 2.3 Application GUIGreeter Note run of program Window for prompt and input Window for Greeting Note improved version, Figure 2.4
- 42. Input Dialog Input dialogs are GUI widgets used to get text input from user Example showInputDialog(prompt); prompt can be a string a graphic image another Java Object
- 43. Message Dialog A GUI widget for displaying information Example showMessageDialog(null, message, title, messageKind); Message kind can be: error, information, warning, question, or plain used by interface manager to display proper icon