JPR_W-19

• Constructor

  A special member which initializes an object immediately upon creation. It has the same name as the class name in which it resides and is syntactically similar to any method.
• Types of constructors

  • Default constructor
  • Parameterized constructor
  • Copy constructor
• Class

  A user defined data type which groups data members and its associated functions together
• Object


  A basic unit of Object Oriented Programming and represents the real life entities
• Methods of FileInputStream Class

  • void close()
  • int read()
  • int read(byte[] b)
  • read(byte[] b, int off, int len)
  • int available()
• Error

  Mistakes that can make a program go wrong. They may be logical or typing mistakes, and can produce incorrect output, terminate execution abruptly, or cause the system to crash.
• Types of errors

  • Compile time errors
  • Runtime errors
• Java API packages

  • java.lang
  • java.util
  • java.io
  • java.awt
  • java.net
  • java.applet
• Array

  A homogeneous data type where it can hold only objects of one data type
• Types of arrays

  • One-Dimensional
  • Two-Dimensional
• Access specifiers in Java

  • public
  • private
  • friendly
  • protected
  • Private Protected
• String

  A major class where length is fixed (immutable) and contents cannot be modified
• StringBuffer

  A peer class of String where length is flexible (mutable) and contents can be modified
• Defining a class Circle

  1. Initialize data members pi and radius

  2. Display values of data members

  3. Calculate and display area of circle
• Exception

  A problem that arises during the execution of a program. Java exception handling is used to handle error conditions systematically.
• Built-in exceptions

  • Arithmetic exception
  • ArrayIndexOutOfBounds Exception
  • ClassNotFoundException
  • FileNotFoundException
  • IO Exception
  • NullPointerException
  • NumberFormatException
  • StringIndexOutOfBoundsException
  • OutOfMemoryException
  • SecurityException
  • StackOverflowException
• drawRect()

  Displays an outlined rectangle. Syntax: void drawRect(int top,int left, int width,int height)
• drawOval()

  Draws an ellipse or circle. Syntax: void drawOval(int top, int left, int width, int height)
• Byte stream class

  Designed for byte streams. InputStream and OutputStream are abstract classes that define Java's model of streaming byte input and output.
• Character stream class

  Designed for character streams. Reader and Writer are abstract classes that define streaming character input and output.
• Applet life cycle

  1. init()

  2. start()

  3. paint()

  4. stop()

  5. destroy()
• Class

  Doesn't support multiple inheritance, uses "extend" keyword to inherit, contains method body
• Interface

  Supports multiple inheritance, uses "implements" keyword to inherit, contains abstract methods (without body)
• Vector

  A dynamic array that can grow or shrink in size as needed
• Creating a vector with 5 elements

  1. Add element 5

  2. Add element 15

  3. Add element 25

  4. Add element 35

  5. Add element 45
• Inserting a new element at the 2nd position

  Insert element 20 at index 1
• Removing the 1st and 4th elements from the vector

  1. Remove element at index 0

  2. Remove element at index 3
• Vector creation and manipulation

  • Vector v = new Vector();
  • v.add(5);
  • v.add(15);
  • v.add(25);
  • v.add(35);
  • v.add(45);
  • v.add(1, 20);
  • v.remove(0);
  • v.remove(3);
• replace()

  Method to replace all occurrences of old Char in a string with new Char
• String s1="Java is a programming language. Java is a platform."

  • String s2=s1.replace("Java","Kava");//replaces all occurrences of "Java" to "Kava"
• Output: Kava is a programming language. Kava is a platform.
• Creating a vector with five elements

  1. addElement(new Integer(5))

  2. addElement(new Integer(15))

  3. addElement(new Integer(25))

  4. addElement(new Integer(35))

  5. addElement(new Integer(45))
• Inserting new element at 2nd position

  insertElementAt(new Integer(20),1)
• Removing 1st and 4th element from vector

  1. removeElementAt(0)

  2. removeElementAt(3)
• Package is both naming and visibility controlled mechanism in Java
• Package

  Mechanism for partitioning the class namespace into more manageable parts
• Packages are mirrored by directories
• package package1; public class Box { ... }

  • import package1.Box; class volume { ... }
• Creating two threads

  1. new Even().start()

  2. new Odd().start()
• Even thread printing even numbers 2 to 50

  for(int i=2;i<=50;i=i+2){ System.out.println("\t Even thread :"+i); sleep(500); }