JPR_S-19

• Features of Java


  • Data Abstraction and Encapsulation
  • Inheritance
  • Polymorphism
  • Platform independence
  • Portability
  • Robust
  • Supports multithreading
  • Supports distributed applications
  • Secure
  • Architectural neutral
  • Dynamic
• finalize() method


  Used to perform specific actions that are to be done when an object is garbage collected
• finalize() method syntax


  protected void finalize() {}
• Integer.parseInt()


  Converts string objects to primitive int
• Integer.toString()


  Converts primitive int to string objects
• Types of inheritances in Java

  • Single level inheritance
  • Multilevel inheritance
  • Hierarchical inheritance
  • Multiple inheritance
  • Hybrid inheritance
• try-catch-finally blocks syntax


  1. try{

  2. //Statements to be monitored for any exception

  3. } catch(ThrowableInstance1 obj) {

  4. //Statements to execute if this type of exception occurs

  5. } catch(ThrowableInstance2 obj2) {

  6. //Statements

  7. }finally{

  8. //Statements which should be executed even if any exception happens

  9. }
• <param> tag syntax


  <param name="name" value="value">
• Stream class


  An I/O Stream represents an input source or an output destination
• Types of stream classes


  • Byte stream classes
  • Character stream classes
• Platform independence and portability in Java

  • Java programs are compiled into bytecode which is platform independent and can be executed on any platform with a Java Virtual Machine (JVM)
  • JVM is a virtual machine which exists inside the computer memory and is a simulated computer within a computer which does all the functions of a computer
• Constructors in Java


  Used to initialize an object as soon as it is created
• Types of constructors


  • Default constructor
  • Constructor with no arguments
  • Parameterized constructor
  • Copy constructor
• Creating threads in Java


  1. By extending the Thread class

  2. By implementing the Runnable interface
• Stream


  A sequence of data
• Java stream


  Composed of bytes
• Input stream class


  • Java application uses an input stream to read data from a source
• Output stream class


  • Java application uses an output stream to write data to a destination
• Input stream


  • May read from a file, an array, peripheral device or socket
• Output stream

  • May be a write to file, an array, peripheral device or socket
• Input stream classes


  • Reads data as bytes
• Output stream classes


  • Writes data as bytes
• Super class of input stream

  Abstract inputStream class
• Super class of output stream

  Abstract OutputStream class
• Methods of input stream

  • public int read() throws IOException
  • public int available() throws IOException
  • public void close() throws IOException
• Methods of output stream

  • public void write(int b) throws IOException
  • public void write(byte[] b) throws IOException
  • public void flush() throws IOException
  • public void close() throws IOException
• Subclasses of input stream

  • File Input stream
  • Byte Array Input Stream
  • Filter Input Stream
  • Piped Input Stream
  • Object Input Stream
  • DataInputStream
• Subclasses of output stream

  • File Output Stream
  • Byte Array Output Stream
  • Filter output Stream
  • Piped Output Stream
  • Object Output Stream
  • DataOutputStream
• Applets


  Event driven
• Applications


  Control driven
• Program to copy content of one file to another file

  1. FileInputStream in= new FileInputStream("input.txt")

  2. FileOutputStream out= new FileOutputStream("output.txt")

  3. int c=0

  4. while(c!=-1)

  5. c=in.read()

  6. out.write(c)

  7. System.out.println("File copied to output.txt....")

  8. if(in!=null) in.close()

  9. if(out!=null) out.close()
• Methods of vector class

  • boolean add(Object obj)
  • Boolean add(int index,Object obj)
  • void addElement(Object obj)
  • int capacity()
  • void clear()
  • Object clone()
  • boolean contains(Object elem)
  • void copyInto(Object[] anArray)
  • Object firstElement()
  • Object elementAt(int index)
  • int indexOf(Object elem)
  • Object lastElement()
  • Object insertElementAt(Object obj,int index)
  • Object remove(int index)
  • void removeAllElements()
• Dynamic method dispatch


  Mechanism by which a call to an overridden method is resolved at run time, rather than compile time
• Program to create two threads

  1. Ascending Thread: for(int i=1; i<=15;i++) System.out.println("Ascending Thread : " + i)

  2. Descending Thread: for(int i=15; i>0;i--) System.out.println("Descending Thread : " + i)

  3. main: Ascending a=new Ascending(); a.start(); Descending d=new Descending(); d.start()
• Command Line Arguments


  Arguments passed at the time of running the java program
• Program to input name and salary of employee and throw user defined exception if entered salary is negative

  1. NegativeSalaryException extends Exception with constructor

  2. main: BufferedReader br, accept name and salary

  3. if(salary<0) throw new NegativeSalaryException("Enter Salary amount isnegative")

  4. catch (NegativeSalaryException a) System.out.println(a)
• Applet life cycle


  • init(): Variable declaration and initialization
  • start(): Actual code of the applet
  • stop(): Stops the execution of the applet
  • destroy(): Removes the applet object from memory
  • paint(): Redraws the output on the applet display area