Java Software Solutions - Chapter 1: Introduction

va Author: Lewis/Loftus // // Demonstrates the basic structure of a Java application. //******************************************************************** public class Lincoln { //----------------------------------------------------------------- // Prints a presidential quote. //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("A quote by Abraham Lincoln:"); System.out.println ("Whatever you are, be a good one."); } } Output A quote by Abraham Lincoln: Whatever you are, be a good one. Java Program Structure public class MyProgram { } // comments about the class class header class body Comments can be placed almost anywhere Copyright © 2012 Pearson Education, Inc. Java Program Structure public class MyProgram { } // comments about the class public static void main (String[] args) { } // comments about the method method header method body Copyright © 2012 Pearson Education, Inc. Comments Comments should be included to explain the purpose of the program and describe processing steps They do not affect how a program works Java comments can take three forms: // this comment runs to the end of the line /* this comment runs to the terminating symbol, even across line breaks */ /** this is a javadoc comment */ Copyright © 2012 Pearson Education, Inc. Identifiers Identifiers are the "words" in a program A Java identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign Identifiers cannot begin with a digit Java is case sensitive: Total, total, and TOTAL are different identifiers By convention, programmers use different case styles for different types of identifiers, such as title case for class names - Lincoln upper case for constants - MAXIMUM Copyright © 2012 Pearson Education, Inc. Identifiers Sometimes the programmer chooses the identifer(such as Lincoln) Sometimes we are using another programmer's code, so we use the identifiers that he or she chose (such as println) Often we use special identifiers called reserved words that already have a predefined meaning in the language A reserved word cannot be used in any other way Copyright © 2012 Pearson Education, Inc. Reserved Words The Java reserved words: abstract assert boolean break byte case catch char class const continue default do double else enum extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while Copyright © 2012 Pearson Education, Inc. Quick Check Copyright © 2012 Pearson Education, Inc. Which of the following are valid Java identifiers? grade quizGrade NetworkConnection frame2 3rdTestScore MAXIMUM MIN_CAPACITY student# Shelves1&2 Quick Check Copyright © 2012 Pearson Education, Inc. Which of the following are valid Java identifiers? grade quizGrade NetworkConnection frame2 3rdTestScore MAXIMUM MIN_CAPACITY student# Shelves1&2 Valid Valid Valid Valid Invalid – cannot begin with a digit Valid Valid Invalid – cannot contain the '#' character Invalid – cannot contain the '&' character White Space Spaces, blank lines, and tabs are called white space White space is used to separate words and symbols in a program Extra white space is ignored A valid Java program can be formatted many ways Programs should be formatted to enhance readability, using consistent indentation See Lincoln2.java and Lincoln3.java Copyright © 2012 Pearson Education, Inc. Outline Computer Processing Hardware Components Networks The Java Programming Language Program Development Object-Oriented Programming Copyright © 2012 Pearson Education, Inc. Program Development The mechanics of developing a program include several activities: writing the program in a specific programming language (such as Java) translating the program into a form that the computer can execute investigating and fixing various types of errors that can occur Software tools can be used to help with all parts of this process Copyright © 2012 Pearson Education, Inc. Language Levels There are four programming language levels: machine language assembly language high-level language fourth-generation language Each type of CPU has its own specific machine language The other levels were created to make it easier for a human being to read and write programs Copyright © 2012 Pearson Education, Inc. Programming Languages Each type of CPU executes only a particular machine language A program must be translated into machine language before it can be executed A compiler is a software tool which translates source code into a specific target language Often, that target language is the machine language for a particular CPU type The Java approach is somewhat different Copyright © 2012 Pearson Education, Inc. Java Translation The Java compiler translates Java source code into a special representation called bytecode Java bytecode is not the machine language for any traditional CPU Another software tool, called an interpreter, translates bytecode into machine language and executes it Therefore the Java compiler is not tied to any particular machine Java is considered to be architecture-neutral Copyright © 2012 Pearson Education, Inc. Java Translation Java source code Machine code Java bytecode Bytecode interpreter Bytecode compiler Java compiler Copyright © 2012 Pearson Education, Inc. Development Environments There are many programs that support the development of Java software, including: Java Development Kit (JDK) Eclipse NetBeans BlueJ jGRASP Though the details of these environments differ, the basic compilation and execution process is essentially the same Copyright © 2012 Pearson Education, Inc. Syntax and Semantics The syntax rules of a language define how we can put together symbols, reserved words, and identifiers to make a valid program The semantics of a program statement define what that statement means (its purpose or role in a program) A program that is syntactically correct is not necessarily logically (semantically) correct A program will always do what we tell it to do, not what we meant to tell it to do Copyright © 2012 Pearson Education, Inc. Errors A program can have three types of errors The compiler will find syntax errors and other basic problems (compile-time errors) If compile-time errors exist, an executable version of the program is not created A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors) A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors) Copyright © 2012 Pearson Education, Inc. Basic Program Development errors? errors? Edit and save program Compile program Execute program and evaluate results Copyright © 2012 Pearson Education, Inc. Outline Computer Processing Hardware Components Networks The Java Programming Language Program Development Object-Oriented Programming Copyright © 2012 Pearson Education, Inc. Problem Solving The purpose of writing a program is to solve a problem Solving a problem consists of multiple activities: Understand the problem Design a solution Consider alternatives and refine the solution Implement the solution Test the solution These activities are not purely linear – they overlap and interact Copyright © 2012 Pearson Education, Inc. Problem Solving The key to designing a solution is breaking it down into manageable pieces When writing software, we design separate pieces that are responsible for certain parts of the solution An object-oriented approach lends itself to this kind of solution decomposition We will dissect our solutions into pieces called objects and classes Copyright © 2012 Pearson Education, Inc. Object-Oriented Programming Java is an object-oriented programming language As the term implies, an object is a fundamental entity in a Java program Objects can be used effectively to represent real-world entities For instance, an object might represent a particular employee in a company Each employee object handles the processing and data management related to that employee Copyright © 2012 Pearson Education, Inc. Objects An object has: state - descriptive characteristics behaviors - what it can do (or what can be done to it) The state of a bank account includes its account number and its current balance The behaviors associated with a bank account include the ability to make deposits and withdrawals Note that the behavior of an object might change its state Copyright © 2012 Pearson Education, Inc. Classes An object is defined by a class A class is the blueprint of an object The class uses methods to define the behaviors of the object The class that contains the main method of a Java program represents the entire program A class represents a concept, and an object represents the embodiment of that concept Multiple objects can be created from the same class Copyright © 2012 Pearson Education, Inc. Class = Blueprint One blueprint to create several similar, but different, houses: Copyright © 2012 Pearson Education, Inc. Objects and Classes Bank Account A class (the concept) John’s Bank Account Balance: $5,257 An object (the realization) Bill’s Bank Account Balance: $1,245,069 Mary’s Bank Account Balance: $16,833 Multiple objects from the same class Copyright © 2012 Pearson Education, Inc. Inheritance One class can be used to derive another via inheritance Classes can be organized into hierarchies Bank Account Account Charge Account Savings Account Checking Account Copyright © 2012 Pearson Education, Inc. Summary Chapter 1 focused on: components of a computer how those components interact how computers store and manipulate information computer networks the Internet and the World Wide Web programming and programming languages an introduction to Java an overview of object-oriented concepts Copyright © 2012 Pearson Education, Inc.