Introduction to Programming and Java

2 The Central Processing Unit The speed of a CPU is controlled by the system clock which generates an electronic pulse at regular intervals One “machine cycle” per pulse which performs a part of a machine language command, for example move info in register A to memory location add contents of register A to register B Computers generate billions of pulses per second What’s a machine language command?

Machine Language Commands A machine language command is the most basic command stored in a computer’s memory. For example: – A machine language program is a sequence of hundreds of such commands. Sound like fun? Early computer programmers didn’t like dealing with machine language so they invented assembly language.

Assembly Language Commands A single assembly language command corresponds to a single machine language command but is easier for a programmer to read/write/understand For example –move #061,1207 A assembly language program is a sequence of hundreds of such commands. Sound like fun? It’s better, but early computer programmers didn’t like dealing with assembly language much either so they invented high level language. finit mov cx,8 mov al,[Y] or al,al jnz LoadX fld1 jmp Exit LoadX: fld [X] dec cx shl al,1

High Level Language Commands A high level language command can correspond to several assembly language commands High level languages also allow programmers to use “names” instead of memory addresses For example: cost = (price – discount) * (1 + taxrate); A high level language program is a sequence of many such commands. Sound like fun? Yes!!!!!!!!!!!!!!!! Grace Hopper

CPU Program Translation I Each type of CPU executes only a particular machine language A high level language 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 high level source code Compiler 8086 machine code

CPU Program Translation 2 Each type of CPU executes only a particular machine language A high level language program must be translated into machine language before it can be executed A interpreter is a software tool which translates source code into a specific target language one line at a time, as needed high level source code Interpreter

8 High Level Languages There are hundreds of different high level languages Each has its strengths and weaknesses We’ll use Java in this course And there are even “higher” level languages called 4 th generation languages

Java A programming language specifies the words and symbols that we can use to write a program A programming language employs a set of rules that dictate how the words and symbols can be put together to form valid program statements The Java programming language was created by Sun Microsystems, Inc. It was introduced in 1995 and it's popularity has grown quickly since

Java Program Structure In the Java programming language: –A program is made up of one or more classes –A class contains one or more methods –A method contains program statements These terms will be explored in detail throughout the course A Java application always contains a method called main See Lincoln.java (page 29) Lincoln.java

11 Java Program Structure public class MyProgram {}{} // comments about the class class header class body Comments can be placed almost anywhere

12 Java Program Structure public class MyProgram {}{} // comments about the class public static void main (String[] args) {}{} // comments about the method method header method body

13 Comments Comments in a program are called inline documentation They 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 */

14 Identifiers Identifiers are the words a programmer uses in a program An 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

Identifiers Sometimes we choose identifiers ourselves when writing a program (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

16 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

17 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.javaLincoln2.java See Lincoln3.javaLincoln3.java Fall Do Lab Here

18 Java Translation The Java compiler (javac) translates Java source code into a special representation called bytecode Java bytecode is not the machine language for any traditional CPU Another software tool (java), 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

19 Java Translation Java source code Machine code Java bytecode Bytecode interpreter (java) Bytecode compiler Java compiler (javac)

Program Development The mechanics of developing a program include several activities –understanding what the program is supposed to do –designing the program –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 Computer programmers didn’t like dealing with all of this at the “command line” level, so they invented software tools that can be used to help with many parts of this process

Development Environments There are many programs that support the development of Java software, including: –Sun Java Development Kit (JDK) –Sun NetBeans –IBM Eclipse –Borland JBuilder –MetroWerks CodeWarrior –BlueJ –jGRASP Though the details of these environments differ, the basic compilation and execution process is essentially the same

22 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 sum = value1 + value2; // correct syntax product = (value1)(value2); // incorrect syntax 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 sum = value1 - value2; // logic error? A program will always do what we tell it to do, not what we meant to tell it to do

23 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)

Basic Program Development errors Edit and save program Compile program Execute program and evaluate results

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

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 classes and objects An application/program can use –the primitive Java language –the Java library classes and objects (and their methods) –“homemade” classes and objects (and their methods)

An example using (mostly) the primitive language //********************************************************* // Sum01.java Author: Joyce // // Demonstrates a simple Java application. //********************************************************* public class Sum01 { public static void main (String[] args) { int value1, value2; int sum; value1 = 7; value2 = 4; sum = value1 + value2; System.out.println ("The sum of " + value1 + " and " + value2 + " is " + sum); }

Java Library Classes Java 2 Platform Standard Edition 5.0 The API Specification (see link off Joyce’s CSC 1051 page) There are almost 3,000 classes Packages/Sub-packages are for organizational purposes, for example –awt: abstract windowing toolkit –lang: fundamental to the Java language

Static Methods can be called directly through the class not the “common” approach.. but the easiest to understand for example, all the methods of the Math class are static: –abs –pow –sqrt –…

An example using some static methods from the Java library Math class //********************************************************* // MathDemo.java Author: Joyce // // Demonstrates using static methods. //********************************************************* public class MathDemo { public static void main (String[] args) { int value1, value2; int sum; value1 = 7; value2 = 4; sum = value1 + value2; System.out.println (value2 + " raised to the " + value1 + " power is " + Math.pow(value2, value1)); System.out.println ("The square root of the sum of " + value1 + " and " + value2 + " is " + Math.sqrt(sum)); } static method call

© 2007 Pearson Addison-Wesley. All rights reserved2-31 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 (among other things) For instance, an object might represent a specific person’s bank account Each bank account object handles the processing and data management related to that account

© 2007 Pearson Addison-Wesley. All rights reserved2-32 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 Note that the state of an object might affect its behaviour

© 2007 Pearson Addison-Wesley. All rights reserved2-33 Classes and Objects An object is defined by a class A class is the blueprint of an object –Typically state is maintained in a set of private variables –Typically public methods define the behaviors of the object A class represents a concept, and an object represents the embodiment of that concept Multiple objects can be created from the same class

© 2007 Pearson Addison-Wesley. All rights reserved2-34 Objects and Classes Bank Account private double balance public double deposit (double amount) A class (the concept) John’s Bank Account balance: $5,257 objects (the realization) Bill’s Bank Account balance: $1,245,069 Mary’s Bank Account balance: $16,833

{ Account acct1 = new Account ("Ted Murphy", 72354, ); Account acct2 = new Account ("Jane Smith", 69713, 40.00); Account acct3 = new Account ("Edward Demsey", 93757, ); acct1.deposit (25.85); double smithBalance = acct2.deposit (500.00); System.out.println ("Smith balance after deposit: " + smithBalance); System.out.println ("Smith balance after withdrawal: " + acct2.withdraw (430.75, 1.50)); acct1.addInterest(); acct2.addInterest(); acct3.addInterest(); System.out.println (); System.out.println (acct1); System.out.println (acct2); System.out.println (acct3); }

public class Experiment04 { public static void main (String[] args) {... PairOfDice dice1 = new PairOfDice(); PairOfDice dice2 = new PairOfDice(); NumberStats stats1 = new NumberStats(); NumberStats stats2 = new NumberStats(); Scanner scan= new Scanner (System.in); DecimalFormat fmt= new DecimalFormat ("0.###"); System.out.print("See result of each dice roll? (Y = Yes) > "); boolean trace = scan.nextLine().equalsIgnoreCase("Y");... System.out.println("\nDice 1: " + dice1.maxString());... dice2 = new PairOfDice(numSides1, numSides2); stats1.submit(dice1.roll());... object creation object use

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