Unit 2 Java Programming Concepts .pdf - Google Drive

Unit No: 2 Java Programming Concepts Pavan R Jaiswal

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Introduction Reflections Boxing, unboxing Object serialization, de-serialization Important Java utility classes Java collection framework

Distributed Programming

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Introduction High level programming language Buzzwords 

Simple Object oriented Architectural neutral Distributed Portable Secure, etc 

Java Programming Concepts

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Introduction

Fig 1 Overview of software development process


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Introduction

Fig 2 Java application running on multiple platforms by making use of JVM


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Java reflection API Java reflection is a process of examining or modifying the runtime behaviour of class at runtime Packages providing classes for reflections 

java.lang.class Java.lang.reflect

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Reflection API mainly used in IDE, debugger, test tools, etc

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Java reflection API Reflection scans your classpath Indexes the metadata Allows you to query it on runtime Saves and collects information to be used for modules in project Reflections consists of two components 

Object that represents various parts of class file A mean for extracting those objects in secure way


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Concerns of using reflection Reflections are powerful, but shall not be used indiscriminately Remember the following concerns while accessing it 1. Performance overhead •Certain JVM optimizations can not be performed 2.Security restrictions •Runtime permission may not be available when running under security manager 3.Exposure of internals •Reflective code breaks abstractions 


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Java.lang.Class class 

Performs mainly two tasks Provides methods to get matadata of a class at runtime Provides methods to examine and change the runtime behaviour of a class 

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Methods of Class class Public string getName() public static Class forName(String className)throws ClassNotFoundException 


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Java.lang.Class methods public Object newInstance()throws InstantiationException,IllegalAccessException public boolean isInterface() public boolean isArray() public boolean isPrimitive() public Class getSuperclass() 


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Java.lang.Class methods public Field[] getDeclaredFields()throws SecurityException public Method[] getDeclaredMethods()throws SecurityException public Constructor[] getDeclaredConstructors()throws SecurityException public Method getDeclaredMethod(String name,Class[] parameterTypes)throws NoSuchMethodException,SecurityException 


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forName() method example class Simple{} class Test{ public static void main(String args[]) throws Exception{ Class c=Class.forName("Simple"); System.out.println(c.getName()); } } Output: Simple


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getClass() method example class Simple{} class Test{ void printName(Object obj){ Class c=obj.getClass(); System.out.println(c.getName()); } public static void main(String args[]){ Simple s=new Simple(); Test t=new Test(); t.printName(s); } } Output: Simple


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The .class syntax class Test{ public static void main(String args[]){ Class c = boolean.class; System.out.println(c.getName()); Class c2 = Test.class; System.out.println(c2.getName()); } } Output: boolean Test


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Determining the class object class Simple{} interface My{} class Test{ public static void main(String args[]){ try{ Class c=Class.forName("Simple"); System.out.println(c.isInterface()); Class c2=Class.forName("My"); System.out.println(c2.isInterface()); }catch(Exception e){System.out.println(e);} } } Output: false true


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Javap tool Javap command disassembles a class file. It displays information about 

Fields Constructors Methods present in a class file 

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Syntax $ javap fully_class_name

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Example $ javap -c Test $ javap -c java.lang.String


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Options of javap tool Options

Description

-help

prints the help message

-l

prints line number and local variable

-c

disassembles the code

-s

prints internal type signature

-sysinfo

shows system info (path, size, date, MD5 hash)

-constants

shows static final constants

-version

shows version information


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Java boxing and unboxing 

Java have eight primitive types

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Each one has corresponding library class of

reference type 

E.g. class java.lang.Integer => type int

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These kinds of classes are called as wrapper

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Wrapper classes are immutable and final


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Java boxing and unboxing Conversion of primitive type to corresponding reference

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type is

called boxing

Conversion of reference type to primitive type is called

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unboxing Advantage: no need of conversion between primitives

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and wrappers manually, so less coding is required


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Java boxing example class BoxingExample1{ public static void main(String args[]){ int a=50; Integer a2=new Integer(a);//Boxing Integer a3=5;//Boxing System.out.println(a2+" "+a3); } } Output: 50 5


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Java unboxing example class UnboxingExample1{ public static void main(String args[]){ Integer i=new Integer(50); int a=i; System.out.println(a); } } Output: 50


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Unboxing with comparison operator class UnboxingExample2{ public static void main(String args[]){ Integer i=new Integer(50); if(i=0; period--) { setChanged(); notifyObservers(new Integer(period)); try { Thread.sleep(100); } catch(InterruptedException e) { System.out.println("Sleep interrupted"); } }} }


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Observable class example ObserverDemo.java class ObserverDemo { public static void main(String args[]) { BeingWatched observed = new BeingWatched(); Watcher observing = new Watcher(); /* Add the observing to the list of observers for observed object. */ observed.addObserver(observing); observed.counter(10); } }


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Observable class example // Output [pavan@localhost Observable]# javac ObserverDemo.java [pavan@localhost Observable]# java ObserverDemo update() called, count is 10 update() called, count is 9 update() called, count is 8 update() called, count is 7 update() called, count is 6 update() called, count is 5 update() called, count is 4 update() called, count is 3 update() called, count is 2 update() called, count is 1 update() called, count is 0 [pavan@localhost Observable]#


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java.util.StringTokenizer class It allows application to break a string into tokens It is a legacy class and retained for compatibility reasons Its methods do not distinguish among identifiers, numbers and quoted strings Its methods do not even recognize and skip comments Declaration 

public class StringTokenizer extends Object implements Enumeration 


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StringTokenizer class methods int countTokens() boolean hasMoreElements() boolean hasMoreTokens() Object nextElement() String nextToken() String nextToken(String delim) 


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StringTokenizer class example // Demonstrating StringTokenizer class import java.util.StringTokenizer; class MyStringTokenizer { public static void main(String a[]){ String msg = "This program gives sample code for String Tokenizer"; StringTokenizer st = new StringTokenizer(msg," "); while(st.hasMoreTokens()){ System.out.println(st.nextToken()); } } }


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StringTokenizer class example // Output [pavan@localhost StringTokenizer]# javac MyStringTokenizer.java [pavan@localhost StringTokenizer]# java MyStringTokenizer This program gives sample code for String Tokenizer [pavan@localhost StringTokenizer]#


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Java collection Collection in Java is a framework. It provides an architecture to store and manipulate group of objects Operations like searching, sorting, insertion, deletion, manipulation etc can be performed by Java collection It is like a single unit of objects It have many interfaces (Set, List, Queue etc) and classes (ArrayList, Vector, LinkedList etc) 


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Hierarchy of collection framework

Fig 4 Hierarchy of collection framework Java Programming Concepts

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Collection interface methods public boolean add(Object element)

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public boolean addAll(Collection c)

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public boolean remove(Object element)

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public boolean removeAll(Collection c)

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public boolean retainAll(Collection c)

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public int size()

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public void clear()

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Collection interface methods public boolean contains(Object element)

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public boolean containsAll(Collection c)

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public Iterator iterator()

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public Object[] toArray()

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public boolean isEmpty()

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public boolean equals(Object element)

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public int hashCode()

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LinkedList class 

It uses doubly linked list to store elements

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It can contain duplicate elements

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It maintains insertion order

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In this manipulation is fast as no shifting needed

in case of element removal 

It can be used as list, stack or queue


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LinkedList example import java.util.*; public class LinkedListDemo{ public static void main(String args[]){ LinkedListal=new LinkedList(); al.add("David"); al.add("Solomon"); Iterator itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } }


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ArrayList class     

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It uses dynamic array for storing the elements It extends AbstractList and implements List It can contain duplicate elements It maintains insertion order It allows random access as it makes use of index Manipulation as lot of shifting needs to be done in case of element removal


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ArrayList example import java.util.*; class ArrayListDemo{ public static void main(String args[]){ ArrayList al=new ArrayList(); al.add("David"); al.add("Solomon"); Iterator itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } }


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HashSet class 

It uses hashtable to store elements

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It extends AbstractSet and implements Set

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Contains unique elements only


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HashSet hierarchy

Fig 5 HashSet hierarchy Java Programming Concepts

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HashSet example import java.util.*; class HashSetDemo{ public static void main(String args[]){ HashSet al=new HashSet(); al.add("David"); al.add("Solomon"); al.add("David"); Iterator itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } }


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TreeSet class 

It contains unique elements only like HashSet

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It implements NavigableSet interface

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It extends SortedSet interface


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TreeSet hierarchy

Fig 6 TreeSet hierarchy Java Programming Concepts

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TreeSet example import java.util.*; class TreeSetDemo{ public static void main(String args[]){ TreeSet al=new TreeSet(); al.add("David"); al.add("Solomon"); al.add("Italy"); Iterator itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } }


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HashMap class 

It contains value based on the key

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It implements Map interface

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It extends AbstractMap class

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It contains only unique elements

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It may have one null key and multiple null values

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It maintains no order


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HashMap hierarchy

Fig 7 HashMap hierarchy


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HashMap example import java.util.*; class HashMapDemo{ public static void main(String args[]){ HashMap hm=new HashMap(); hm.put(100,"David"); hm.put(101,"Solomon"); for(Map.Entry m:hm.entrySet()){ System.out.println(m.getKey()+" "+m.getValue()); } } }


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TreeMap class It contains values based on the key It implements NavigableMap interface It extends AbstractMap class It contains only unique elements It can not have null key but can have multiple null values It is same as HashMap instead maintains ascending order 


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TreeMap hierarchy

Fig 8 TreeMap hierarchy


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TreeMap example import java.util.*; class TreeMapDemo{ public static void main(String args[]){ TreeMap hm=new TreeMap(); hm.put(101,"Solomon"); hm.put(100,"David"); hm.put(102,"Italy"); for(Map.Entry m:hm.entrySet()){ System.out.println(m.getKey()+" "+m.getValue()); } } } Java Programming Concepts

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Vector class It implements growable array of objects Similar to array, its elements can be accessed by using integer index Size of vector can grow or shrink as needed It is synchronized, means it is suitable for threadsafe operations  It is a legacy class It used Enumeration interface to traverse the elements, but it can use iterator also 


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Vector example import java.util.*; class VectorDemo{ public static void main(String args[]){ Vector v=new Vector(); v.add("Italy"); v.addElement("Solomon"); v.addElement("David"); Enumeration e=v.elements(); while(e.hasMoreElements()){ System.out.println(e.nextElement()); } } }


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Stack class 

It is subclass of Vector class

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It implements standard last-in first-out stack

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It only defines default constructor, which creates

an empty stack 

It includes all the methods defined by Vector, as

well as adds several of its own


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Stack class methods 

boolean empty()

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Object peek( )

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Object pop( )

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Object push(Object element)

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int search(Object element)


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Stack example import java.util.*; class StackDemo { static void showpush(Stack st, int a) { st.push(new Integer(a)); System.out.println("push(" + a + ")"); System.out.println("stack: " + st); } static void showpop(Stack st) { System.out.print("pop -> "); Integer a = (Integer) st.pop(); System.out.println(a); System.out.println("stack: " + st); } Java Programming Concepts

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Stack example public static void main(String args[]) { Stack st = new Stack(); System.out.println("stack: " + st); showpush(st, 42); showpush(st, 66); showpush(st, 99); showpop(st); showpop(st); showpop(st); try { showpop(st); } catch (EmptyStackException e) { System.out.println("empty stack"); } } }


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Dictionary class It is an abstract class It represents a key/value storage repository and operates much like Map Given a key and value, you can store the value in dictionary After value is stored, it can be retrieved by using key Like Map, this can be though as a list of key/value pairs 


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Dictionary class methods Enumeration elements( )

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Object get(Object key)

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boolean isEmpty( )

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Enumeration keys( )

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Object put(Object key, Object value)

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Object remove(Object key)

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int size( )

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HashTable class It is an array of List Each list is known as bucket hashCode() method identifies position of bucket It implements Map interface It extends Dictionary class It contains only unique elements It may not have any null key or value It is synchronized 


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HashTable example import java.util.*; class HashTableDemo{ public static void main(String args[]){ Hashtable hm=new Hashtable(); hm.put(100,"David"); hm.put(102,"Solomon"); for(Map.Entry m:hm.entrySet()){ System.out.println(m.getKey()+" "+m.getValue()); } } }


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Iterator in Java To generate successive elements from series, we can use Java iterator Its an improvement over Enumeration interface Important points We can iterate only in one direction Iteration can only be done once If you reach end of series, its done. In case of restart, get a new iterator again 


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Iterator methods 

boolean hasNext()

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Object next()

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void remove()


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Iterator example import java.util.ArrayList; import java.util.List; import java.util.ListIterator; public class MyListIterator { public static void main(String a[]){ List li = new ArrayList(); ListIterator litr = null; li.add(23); li.add(98); li.add(29); litr=li.listIterator(); System.out.println("Elements in forward directiton \n"); while(litr.hasNext()){ System.out.print(" "+ litr.next()); } System.out.println("\n Elements in backward while(litr.hasPrevious()){ System.out.print(" " + litr.previous()); } }}


directiton

\n");

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Reference 1. 2.

3. 4.

5. 6. 7. 8.

9.

Java Complete Reference by Herbert Schiedlt Web Technologies: HTML, JS, PHP, Java, JSP, ASP.NET, XML, AJAX, Black Book, DreamTech, ISBN: 978-81-7722-997-4 http://www.javatpoint.com/java-reflection https://docs.oracle.com/javase/tutorial/java/data/autoboxing.ht ml http://www.tutorialspoint.com/java/util/ https://docs.oracle.com/javase/tutorial/collections/intro/ http://www.javatpoint.com/collections-in-java http://www.tutorialspoint.com/java/java_collections.htm http://beginnersbook.com/2014/07/hashtable-in-java-withexample/


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Thank You


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Unit 2 Java Programming Concepts .pdf - Google Drive

Unit 2 Java Programming Concepts .pdf - Google Drive

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