Computer Hardware. Java Software Solutions Lewis & Loftus. Key Hardware Components 12/17/2013

Transcription

1 Java Software Solutions Lewis & Loftus Chapter 1 Notes Computer Hardware Key Hardware Components CPU central processing unit Input / Output devices Main memory (RAM) Secondary storage devices: Hard drive CD / DVD USB (flash) drives Tape / floppies / etc. 1

2 Computer Software Operating System Core software, must be loaded into memory first Provides a user interface, controls the hardware Windows Linux Applications Any software other than the operating system Word processing, spreadsheets, , web browsers, editors, etc. Binary Numbers Binary means base 2. In our daily work, we use decimal which means base 10. Computers use binary. Learn the powers of 2 NOW, up to the 10 th power at least. 2 0 = 1 (Remember: any number to the zero power = 1) 2 1 = = = 8 You figure out the rest. 2

3 Computer Programming Program a set of instructions that tell the computer how to perform a task Programmer a person who writes computer programs Programming language a set of words and symbols that are used to write a program. Each programming language has its own set of rules. Java Programming Language Java is an object-oriented programming language Steps to writing and using a Java program: 1. Write the instructions in the Java language 2. Enter the instructions into an editor and save the file with the extension.java. This file is called the source code. 3. Compile the source code using a program called the Java compiler. The Java compiler creates a new file called the byte code. 4. Run the byte code using a program called the Java interpreter. 5. Were there errors? Fix the errors and go back to step 3 until it works. 3

4 First Java Program public class Lincoln } public static void main (String [] args) } System.out.println( A quote by Abraham Lincoln: ); System.out.println( Whatever you are, be a good one. ); Type carefully! 3 critical elements: Punctuation Spelling Capitalization First Java Program - Comments // demonstrates the basic structure of a Java application public class Lincoln } public static void main (String [] args) } System.out.println( A quote by Abraham Lincoln: ); System.out.println( Whatever you are, be a good one. ); Comments begin with // Comments explain what the program does. Comments are for humans. The compiler ignores them. Sprinkle comments throughout every program. We do not want a drought or a deluge! 4

5 First Java Program - Indentation public class Lincoln... public static void main (String [] args)... System.out.println( A quote by Abraham Lincoln: ); System.out.println( Whatever you are, be a good one. ); } <<< } <<< Indent 3 spaces (press the space bar 3 times) each time you open a curly brace. Move back 3 spaces to the left each time before you close a curly brace. First Java Program Curly Braces public class Lincoln public static void main (String [] args) System.out.println( A quote by Abraham Lincoln: ); System.out.println( Whatever you are, be a good one. ); } // end main } // end class Instructor s Preferred Style: Place opening (left) curly brace at the end of a line of code. Every closing (right) curly brace goes on a line all by itself. Every closing (right) curly braces has a comment. 5

6 Identifiers & Reserved Words Identifiers words and names of things in a program words that the programmer makes up words that another programmer chose words that are reserved for special purposes These special purpose words are called reserved words. You cannot use reserved words as names of things in your program. Memorize the list of reserved words (53 of them) Rules for Creating Identifiers A valid identifier: Starts with a letter Contains only letters, digits, $ or _ (underscore) Cannot be a reserved word Identifiers are case-sensitive total is different from Total shoesize is different from shoesize Examples of valid identifiers: total MAX_HEIGHT num3 keyboard System 6

7 White Space white space separates words and symbols white space characters are: space tab newline character (Enter key pressed) white space is ignored by the compiler be consistent with your spacing (see the earlier slide on indentation) Edit, Compile, Debug, Interpret Step 1: Type your program into an editor. JGrasp, Kate, Notepad, Wordpad, DOS editor Save the program as SomeName.java Step 2: Compile the program with the Java Compiler. javac SomeName.java (or if you re using JGrasp, there s a button) Step 3: If there are syntax errors, go back to step 1 and fix them! Step 4: Interpret (run) your program. java SomeName (yes, JGrasp has a button) 7

8 Kinds of Errors Syntax errors spelling, punctuation, wrong words, or words out of order Syntax refers to the rules that you must follow in order to write statements in the language (in this case Java). If you don t follow the rules, you get a syntax error when you compile. Run-time errors something that happens when the program is running that causes it to crash. Java calls these exceptions. Logic error (book says logical ) The program compiles and runs, but doesn t give the right answer. Object Oriented Programming Class template or pattern Object specific thing created from a class Example: Class == Car Objects: John s Blue Chevy Michelle s Green Prius Each object has its own attributes and methods. attributes values such as blue and Chevy methods what a Car can do 8