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Overview of Java

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Overview of Java

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Overview of Java

  1. 1. Mobile Website Development Overview of Java Facilitated by: Michael Wakahe Tawi Commercial Services Ltd Jul 2011
  2. 2. Table of Contents  Introduction  Data Types and Operators  Program Control Statements  Methods, Classes & Objects  Other Topics  Exercise Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  3. 3. Introduction Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  4. 4. Introduction  Originally developed by James Gosling at Sun Microsystems - 1991  Derives much of its syntax from C and C++  Applications are typically compiled to bytecode (class file) that can run on any Java Virtual Machine (JVM) Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  5. 5. Introduction  Is a general-purpose, concurrent, class-based, object-oriented language  “Write once, run anywhere"  Current stable release: Java Standard Edition 6 (1.6.0) Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  6. 6. Introduction Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  7. 7. Introduction Can be broken down into:  Java Card  Micro Edition (ME)  Standard Edition (SE)  Enterprise Edition (EE) Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  8. 8. Introduction /* This is a simple Java program. Call this file Example.java. Compile and run in Eclipse. */ class Example { // A Java program begins with a call to main(). public static void main(String args[]) { System.out.println("Java drives the Web."); } } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  9. 9. Introduction /* This demonstrates a variable. Call this file Example2.java. Compile and run in Eclipse. */ class Example2 { public static void main(String args[]) { int var1; // this declares a variable int var2; // this declares another variable var1 = 1024; // this assigns 1024 to var1 System.out.println("var1 contains " + var1); var2 = var1 / 2; System.out.print("var2 contains var1 / 2: "); System.out.println(var2); } } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  10. 10. Data Types and Operators Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  11. 11. Data Types and Operators • Contains 2 general categories of built-in data types: object-oriented and non-object oriented. • There are eight primitives • Primitive means these types are not objects but rather normal binary values Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  12. 12. Data Types and Operators Type Meaning boolean Represents true/false values byte 8-bit integer char Character double Double-precision floating point float Single-precision floating point int Integer long Long integer short Short integer Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  13. 13. Data Types and Operators • Contains 2 general categories of built-in data types: object-oriented and non-object oriented. • There are eight primitives • Primitive means these types are not objects but rather normal binary values Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  14. 14. Data Types and Operators • An operator is a symbol that tells the compiler to perform a specific mathematical or logical manipulation. • Java has four general classes of operators: arithmetic, bitwise, relational, and logical. Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  15. 15. Data Types and Operators Arithmentic operator examples:  + implies addition  / implies division  % implies modulus  ++ implies increment Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  16. 16. Data Types and Operators  Relational refers to the relationships that values can have with one another  Examples include:  == implies Equal to  != implies Not Equal to  > implies Greater than  <= implies Less than or Equal to Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  17. 17. Data Types and Operators  Logical refers to the ways in which true and false values can be connected together  Examples include:  & implies AND  | implies OR  ! implies NOT  && implies Short-circuit AND Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  18. 18. Data Types and Operators  The outcome of the relational and logical operators is a boolean value.  The Assignment operator: var = expression; Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  19. 19. Data Types and Operators • Approximately 50 keywords are currently defined in the Java language • Examples: enum, true, false, null, import, do, break, for, int Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  20. 20. Data Types and Operators  An identifier is a name given to a method, a variable, or any other user-defined item  Identifiers can be from one to several characters long  Variable names may start with any letter of the alphabet, an underscore, or a dollar sign. Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  21. 21. Program Control Statements Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  22. 22. Program Control Statements • The if statement • if(condition) statement; • Example: if(10 < 11) System.out.println("10 is less than 11"); Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  23. 23. Program Control Statements  The general form of the if, using blocks of statements, is: if(condition) { statement sequence } else { statement sequence } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  24. 24. Program Control Statements • A common programming construct that is based upon the nested if is the if-else-if ladder. if(condition) statement; else if(condition) statement; else if(condition) statement; ... else statement; Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  25. 25. Program Control Statements • The for Loop: • for(initialization; condition; iteration) statement; • Example for(count = 0; count < 5; count = count+1) System.out.println("This is count: " + count); Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  26. 26. Program Control Statements • The Switch statement: switch(expression) { case constant1: statement sequence break; case constant2: statement sequence break; case constant3: statement sequence break; ... default: statement sequence } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  27. 27. Program Control Statements int i = … switch(i) { case 0: System.out.println("i is zero"); break; case 1: System.out.println("i is one"); break; case 2: System.out.println("i is two"); break; break; default: System.out.println("i is three or more"); } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  28. 28. Program Control Statements  The general form of the while loop is: while(condition) statement;  Example: // print the alphabet using a while loop char ch; ch = 'a'; while(ch <= 'z') { System.out.print(ch); ch++; } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  29. 29. Program Control Statements • The general form of the do-while loop is do { statements; } while(condition); • Very similar to while loop Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  30. 30. Methods, Classes & Objects Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  31. 31. Classes & Objects  Java’s basic unit of encapsulation is the class  A class defines the form of an object  It specifies both the data and the code that will operate on that data Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  32. 32. Classes & Objects  Java uses a class specification to construct objects  Objects are instances of a class.  Thus, a class is essentially a set of plans that specify how to build an object Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  33. 33. Classes & Objects • The general form of a class definition: class classname { // declare instance variables type var1; type var2; // ... type varN; // declare methods type method1(parameters) { // body of method } type method2(parameters) { // body of method } // ... type methodN(parameters) { // body of method } } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  34. 34. Classes & Objects  How objects are declared: Classname referenceName = new Classname(arguments);  The general form of a method is: ret-type name( parameter-list ) { // body of method } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  35. 35. Classes & Objects  A constructor initializes an object when it is created. • A simple example that uses a constructor: // A simple constructor. class MyClass { int x; MyClass() { x = 10; } } Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  36. 36. Other Topics Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  37. 37. Other Topics • Casting: A cast is an instruction to the compiler to convert one type into another. • A cast has this general form: (target-type) expression Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  38. 38. Other Topics • Inheritance is the process by which one object can acquire the properties of another object. • Use of hierarchies. • The inheritance mechanism that makes it possible for one object to be a specific instance of a more general case Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  39. 39. Other Topics  Polymorphism - “one interface, multiple methods.”  This means that it is possible to design a generic interface to a group of related activities. Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  40. 40. Other Topics • Packages are groups of related classes. • Packages help organize your code and provide another layer of encapsulation. • An interface defines a set of methods that will be implemented by a class. Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  41. 41. Other Topics  An interface does not, itself, implement any method.  It is a purely logical construct.  Packages and interfaces give you greater control over the organization of your program Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  42. 42. Other Topics  An exception is an error that occurs at run time.  Using Java’s exception handling subsystem you can, in a structured and controlled manner, handle run-time errors.  Use try-catch and Throwable Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  43. 43. Other Topics  Java has built-in support for multithreaded programming.  A multithreaded program contains two or more parts that can run concurrently.  Each part of such a program is called a thread, and each thread defines a separate path of execution.  Thus, multithreading is a specialized form of multitasking. Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  44. 44. Exercise Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  45. 45. Exercise • Program to simulate a School • Attributes of school include: – Name – Location • School has Teacher and Students Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  46. 46. Exercise • Teacher has: – First & Last Name – Course taught – Years employed Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  47. 47. Exercise • Student has: – First & Last Name – 5 subjects with grades – Can get average grade – Has a fee balace Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.
  48. 48. The End Michael Wakahe michael@tawi.mobi +254 (0)20 239 3052 www.tawi.mobi Copyright © Tawi Commercial Services Ltd. 2015. All Rights Reserved.

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