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Introduction To Computer and Java
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Introduction To Computer and Java

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  • 1. AN OVERVIEW OF COMPUTERS & PROGRAMMING LANGUAGES
  • 2. GOALS  To understand the activity of programming  To learn about the components of computers  To learn about level of programming languages  To become familiar with your computing environment and your compiler  To compile and run your first Java program  To recognize 3 types of errors
  • 3. What is Programming?  Computer programming  the art and science of designing and writing computer programs.  Computer program  a sequences of instructions written in a programming language to achieve a task/to solve a problem.
  • 4. What is a computer?  Hardware  the physical, tangible parts of a computer  keyboard, monitor, disks, wires, chips, etc.  Software  programs and data  a program is a series of instructions  A computer requires both hardware and software  Each is essentially useless without the other
  • 5. Computer System Organization Hardware •CPU •Main Memory (RAM) •Secondary Storage •I/O Device Software •System Programs •Application Programs Computer Organization
  • 6. Hardware Components of a Computer
  • 7. Hardware Components of a Computer – motherboard processor chip adapter cards memory chips memory slots motherboard Expansion slots for adapter cards
  • 8. Hardware Components of a Computer CPU Brain of the computer, most expensive, the faster computer. CPU components– control unit, program counter, register instruction, arithmetic logic unit, accumulator. RAM Temporary memory, volatile, directly connected to the CPU, using memory cells unit.
  • 9. SECONDARY STORAGE •Provides permanent storage for information. •Examples of secondary storage: •Hard disks •Floppy disks •Zip disks •CD-ROMs •Tapes. Hardware Components of a Computer
  • 10. RAM vs Secondary Storage  Primary memory  volatile  Fast  Expensive  Low capacity  Works directly with the processor  Secondary Storage  Nonvolatile  Slow  Cheap  Large capacity  Not connected directly to the processor
  • 11. INPUT DEVICES Sheet-fed Hardware Components of a Computer
  • 12. OUTPUT DEVICES Hardware Components of a Computer
  • 13. CPU and Main Memory Central Processing Unit Main Memory Chip that executes program commands Eg. Intel Pentium 4 Sun ultraSPARC III Primary storage area for programs and data that are in active use Synonymous with RAM
  • 14. Secondary Memory Devices Central Processing Unit Main Memory Floppy Disk Hard Disk Secondary memory devices provide long-term storage Information is moved between main memory and secondary memory as needed Hard disks Floppy disks USB drives Writable CDs Writable DVDs Tapes
  • 15. Input / Output Devices Central Processing Unit Main Memory Floppy Disk Hard Disk Monitor Keyboard I/O devices facilitate user interaction Monitor screen Keyboard Mouse Joystick Bar code scanner Touch screen
  • 16. Software  In contrast to hardware, software is an abstract, intangible entity.  Software can be categorized as system or application software (refer next slide)  It consists of program and data to be used to perform certain tasks  A program is a sequence of simple steps and operations, stated in a precise language that the hardware can interpret  The process of programming involve algorithm design & coding.
  • 17. Software Categories  System Software  Systems programs keep all the hardware and software running together smoothly  The most important system software is the operating system (OS)  controls all machine activities  provides the user interface to the computer  manages resources such as the CPU, memory & I/O  Windows XP, Unix, Linux, Mac OS  Application Software  generic term for any other kind of softwares  word processors, Spreadsheets, Web browsers, games
  • 18. Algorithm Algorithm refers to the strategy to solve a problem It is a clear step by step sequence of instructions that describes how to accomplish a certain task. 2 ways can be used to represent algorithm: a) pseudocode - using english-like-phrases to describe the algorithm b) flowchart -using diagrams that employ the symbol to describe the algorithm.
  • 19. Coding Algorithm need to be translated into computer language so that it can be executed Coding refers to the process of expressing algorithm in a programming language The product of coding is a program. The act of carrying out the instructions contained in a program is called program execution  A computer program is stored internally as a series of binary numbers known as the machine language of the computer
  • 20. Digital Information  Computers store all information digitally:  numbers  text  graphics and images  video  audio  program instructions  In some way, all information is digitized - broken down into pieces and represented as numbers
  • 21. Representing Text Digitally  For example, every character is stored as a number, including spaces, digits, and punctuation  Corresponding upper and lower case letters are separate characters H i , H e a t h e r . 72 105 44 32 72 101 97 116 104 101 114 46
  • 22. p. 4.15 Fig. 4-16 Next The ASCII data set  128 characters (0 until 127) Character A in ASCII  01000001 American Standard Code for Computer InterChange (ASCII)
  • 23. Binary Numbers  Once information is digitized, it is represented and stored in memory using the binary number system  A single binary digit (0 or 1) is called a bit  A byte consists of 8 bits.  Each byte in main memory resides at a numbered location called its address.
  • 24. Memory 24 Main memory is divided into many memory locations (or cells) 9278 9279 9280 9281 9282 9283 9284 9285 9286 Each memory cell has a numeric address, which uniquely identifies it
  • 25. Storing Information 25 9278 9279 9280 9281 9282 9283 9284 9285 9286 Large values are stored in consecutive memory locations 10011010 Each memory cell stores a set number of bits (usually 8 bits, or one byte)
  • 26. Main Memory
  • 27. Storage Capacity  Every memory device has a storage capacity, indicating the number of bytes it can hold  Capacities are expressed in various units: 27 KB 2 10 = 1024 MB 2 20 (over 1 million) GB 2 30 (over 1 billion) TB 2 40 (over 1 trillion) Unit Symbol Number of Bytes kilobyte megabyte gigabyte terabyte
  • 28. Language Levels  Levels of programming language levels:  machine language  assembly language  high-level 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 28
  • 29. Programming Languages Machine language 101101100110 011011010 Assembly language iload intRate bipush 100 if_icmpgt intError High-level language if (intRate > 100) . . .
  • 30. Programming Languages  Each type of CPU executes instructions only in 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 from high level language into a specific machine language  An assembler translates from assembly language into a specific machine language 30
  • 31. Language Description Examples Translator Machine Instruction in 0 and 1 bits 0111000011000 001 None Assembly Instruction in mnemonic code LOAD 3 STOR 4 ADD assembler High-level Similar to human language, FORTRAN, COBOL, Pascal, C, C++, Java… sum = 4 + 3; Compiler & interpreter Programming Languages
  • 32. The Java Programming Language  Created by Sun Microsystems, Inc. introduced in 1995 and it's popularity has grown quickly since Rich library Platform-independent ("write once, run anywhere") or architecture-neutral
  • 33. 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 Java software tool, called an interpreter (or Java Virtual Machine (JVM)) , translates bytecode into machine language and executes it 33
  • 34. Java Translation 34 Java source code (program) Machine code Java bytecode Bytecode interpreter Java compiler
  • 35. Portability  After compiling a Java program into byte-code, that byte-code can be used on any computer with a byte- code interpreter and without a need to recompile.  Byte-code can be sent over the Internet and used anywhere in the world.  This makes Java suitable for Internet applications.
  • 36. Becoming Familiar with your Computer to use Java  Understand files and folders/directories  Locate the Java compiler/ Install J2SE  Set path & Java class path  Write a simple program (later)  Save your work  Compile & run  Use Dos Command Prompt or IDE
  • 37. A DOS Command Window
  • 38. An Integrated Development Environment
  • 39. File Hello.java 1 public class Hello 2 { 3 public static void main(String[] args) 4 { 5 // display a greeting in the console window 6 System.out.println("Hello, World!"); 7 } 8 }
  • 40. Java Program Elements  A Java program is made up of class definitions.  A class definition must contains a header and a body.  A class contains zero or more methods  A method is a named section of code that also has a header & body  A method contains program statements  Single-line (starts with //) and multi-line (enclosed by /* and */) comments are used to document the code
  • 41. Java Program Structure 41 public class Hello { } // comments about the class class header class body //Comments can be placed almost anywhere
  • 42. Java Program Structure 42 public class MyProgram { } // comments about the class public static void main (String[] args) { } // comments about the method method header method body
  • 43. Compiling and Running Type program into text editor Save (file name must be similar to class name) Open Dos Window Change directory to saved file directory Compile into byte codes javac Hello.java Execute byte codes java Hello
  • 44. Hello.java javac Hello.class java Class Loader Processing a Java Program
  • 45. Class Loader  A Java program typically consists of several pieces called classes.  Each class may have a separate author and each is compiled (translated into byte-code) separately.  A class loader (called a linker in other programming languages) automatically connects the classes together and loads the compiled code (bytecode) into main memory.
  • 46. JVM Create/modify source code Source code Compile source code Byte code Run byte code Output Syntax errors Runtime errors or incorrect results Creating a Java Program…
  • 47. Errors  It is common for programmer to make mistake in a program.  Three kinds of errors  Syntax errors  Runtime errors  Logic errors
  • 48. Syntax Errors  Grammatical mistakes in a program  The grammatical rules for writing a program are very strict  The compiler catches syntax errors and prints an error message.  Example: using a period where a program expects a semicolon  System.out.print("..."),  System.out.print("Hello);
  • 49. Runtime Errors  Errors that are detected when your program is running, but not during compilation  When the computer detects an error, it terminates the program and prints an error message.  Example: attempting to divide by 0
  • 50. Logic Errors  Errors that are not detected during compilation or while running, but which cause the program to produce incorrect results  Example: an attempt to calculate a Fahrenheit temperature from a Celsius temperature by multiplying by 9/5 and adding 23 instead of 32  E.g  System.out.print("Hell");