Java 7
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Here is an example of inheritance in Java: ```java class Employee { String name; int id; public Employee(String name, int id) { this.name = name; this.id = id; } } class Programmer extends Employee { String language; public Programmer(String name, int id, String language) { super(name, id); this.language = language; } } ``` Here Employee is the base/super class and Programmer is the derived/sub class that inherits from Employee. Programmer extends Employee and uses super() to pass values to the Employee constructor.
![Day-4
Session-1 Session-2
------------- -------------
IO Multi-Threading
Char and byte oriented streams Creating threads: using Thread class and Runnable
interface
BufferedReader and BufferedWriter
Thread life cycle
File handling
Using sleep(), join(), thread priorities
Object Serialization and IO Synchronization
[ObjectInputStream /
ObjectOutputStream] Solving producer and consumer problem using
wait() and notify()
Deadlock introduction
Concurrency Utilities Overview
Executor Framework, Semaphore, Latches
6 rgupta.trainer@gmail.com](https://image.slidesharecdn.com/java7new-130123031103-phpapp01/85/Java-7-6-320.jpg)
![Array
One Dimensional array
int x[]=new int[5]
22 rgupta.trainer@gmail.com](https://image.slidesharecdn.com/java7new-130123031103-phpapp01/85/Java-7-22-320.jpg)
![Session-1
Char and byte oriented streams
BufferedReader and BufferedWriter
File handling
Object Serialization
[ObjectInputStream / ObjectOutputStream]
109 rgupta.trainer@gmail.com](https://image.slidesharecdn.com/java7new-130123031103-phpapp01/85/Java-7-109-320.jpg)
![File
File abstraction that FileReader
represent file and
char[] in = new char[50]; // to store input
directories int size = 0;
FileReader fr =new FileReader(file);
File f=new File("....");
boolean flag= file.createNewFile(); size = fr.read(in); // read the whole file!
boolean flag= file.mkDir(); System.out.print(size + " "); // how many
bytes read
boolean flag=file.exists();
FileWriter for(char c : in) // print the array
System.out.print(c);
File file = new File( "fileWrite2.txt");
FileWriter fw =new FileWriter(file); fr.close(); // again, always close
fw.write("howdynfolksn"); // write characters to
fw.flush(); // flush before closing
fw.close(); // close file when done
115 rgupta.trainer@gmail.com](https://image.slidesharecdn.com/java7new-130123031103-phpapp01/85/Java-7-115-320.jpg)
![fundamental diff bw ArrayList and
LinkedList
ArrayLists manage arrays internally.
[0][1][2][3][4][5] ....
List<Integer> arrayList = new ArrayList<Integer>();
LinkedLists consists of elements where each element has
a reference to the previous and next element
[0]->[1]->[2] ....
<- <-
161 rgupta.trainer@gmail.com](https://image.slidesharecdn.com/java7new-130123031103-phpapp01/85/Java-7-161-320.jpg)
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Java 7
- 1. Core Java Rajeev Gupta MTech CS
- 2. Contents at a glance Java An Introduction Basic Java Constructs and Data Types and array OO Introduction Class object and related topics Inheritance Final ,Abstract Classes and interface String class, immutability, inner classes Exceptions Handling, assertions Streams and Input/output Files, serialization Java Thread Java Collections 2 [email protected]
- 3. Day-1 Session-1 ------------- Session-2 Introduction to Java ------------- What is Java,Why Java? Object Oriented JDK,JRE and JVM discussion Object, class, Encapsulation, Installing JDK, eclipse,javadoc Abstraction, Hello World application Inheritence, Procedural Programming Polymorphism,message passing If..else,switch, looping ( concepts only, implementation on day 2) Array Examples 3 [email protected]
- 4. Day-2 Session-1 Session-2 ------------- ------------- Inheritance Class and objects Type of inheritance, diamond problem InstanceOf operator Creating Classes Final Implementing Methods Final variable, final method , final class Object: state, identity and behaviour Acess control: public, private,protected and default Constructors: default, parameterized and copy Packages Instance variable, static variable and local variable Abstract class Interface Initialization block Polymorphism Static method and applications Overloading Packages and visibility modifier: public, Overriding protected, private and default Type of relationship bw objects IS-A, HAS-A, USE-A 4 [email protected]
- 5. Day-3 Session-1 ------------- Session-2 String class: Immutability and usages, ------------- stringbuilder and stringbuffer Exception handling Wrapper classes and usages Try, catch, throw, throws, Java 5 Language Features (I): finally Checked and AutoBoxing and Unboxing, Enhanced For loop, Varargs, Static Import, Unchecked exception Enums User defind exceptions design by contract- assertions Inner classes Regular inner class, method local inner class, annonymous inner class 5 [email protected]
- 6. Day-4 Session-1 Session-2 ------------- ------------- IO Multi-Threading Char and byte oriented streams Creating threads: using Thread class and Runnable interface BufferedReader and BufferedWriter Thread life cycle File handling Using sleep(), join(), thread priorities Object Serialization and IO Synchronization [ObjectInputStream / ObjectOutputStream] Solving producer and consumer problem using wait() and notify() Deadlock introduction Concurrency Utilities Overview Executor Framework, Semaphore, Latches 6 [email protected]
- 7. Day-5 Session-1 Session-2 ------------- ------------- Collections Framework Java 5 Language Features II List, Map, Set usages introduction Generics Usages ArrayList, LinkedList, HashMap, Annotations TreeMap, HashSet Comparable, Comparator interface implementation Case study using collection, File User define key in HashMap MCQ Exam 7 [email protected]
- 9. Session-1 Introduction to Java What is Java,Why Java? JDK,JRE and JVM discussion Installing JDK, eclipse,javadoc Hello World application Procedural Programming If..else,switch, looping Array Examples 9 [email protected]
- 10. What is Java? Java is not only an oo programming language It can be best described as OOPS+JVM+API 10 [email protected]
- 11. How Sun define Java? Simple and Powerful Object Oriented Portable Architecture Neutral Distributed Multi-threaded Robust, Secure/Safe Interpreted High Performance Dynamic programming language/platform. 11 [email protected]
- 13. Versions JDK 1.0 (1995) JDK 1.1 (1997) J2SE 1.2 (1998) ) Playground J2SE 1.3 (2000) Kestrel Called Java2 J2SE 1.4 (2002) Merlin J2SE 5.0 (2004) Tiger Java SE 6 ( 2006) Mustang Version for the session Java SE 7 (2011) Dolphin 13 [email protected]
- 14. Some common buzzwords JDK Java development kit, developer need it Byte Code Highly optimize instruction set, designed to run on JVM Platform independent JRE Java Runtime environment, Create an instance JVM, must be there on deployment machine. Platform dependent JVM Java Virtual Machine JVM Pick byte code and execute on client machine Platform dependent… 14 [email protected]
- 16. Hello World Lab set-up Java 1.7 Eclipse 4.2 ( eclipse juno) Java doc 1.7 16 [email protected]
- 17. Analysis of Hello World !!! 17 [email protected]
- 18. Java Program Structure Documentation Section Package Statement Import Statements Interface Statements Class Declarations Main Method Class { } 18 [email protected]
- 19. Java Data Type 2 type Primitive data type Reference data type (latter) 19 [email protected]
- 20. Primitive data type: boolean either true of false char 16 bit Unicode 1.1 byte 8-bit integer (signed) short 16-bit integer (signed) int 32-bit integer (signed) long 64-bit integer (singed) float 32-bit floating point (IEEE 754-1985) double 64-bit floating point (IEEE 754-1985) Java uses Unicode to represent characters internally 20 [email protected]
- 21. Procedural Programming if..else switch Looping; for, while, do..while as usual in Java as in C/C++ Don’t mug the program/logic Follow dry run approach Try some programms: Create Factorial program Prime No check Date calculation 21 [email protected]
- 22. Array One Dimensional array int x[]=new int[5] 22 [email protected]
- 23. Session-2 Object Oriented Concepts Object, class Basic principles of OO Encapsulation Abstraction modularity Inheritance/ Hierarchy Polymorphism, message passing 23 [email protected]
- 24. So what is object orientation? 24 [email protected]
- 25. What is an Object? 25 [email protected]
- 26. What is an class? 26 [email protected]
- 27. What is the relationship bw class and objects? 27 [email protected]
- 28. Basic principles of OO 28 [email protected]
- 33. A bit about UML diagram… UML 2.0 aka modeling language has 12 type of diagrams Most important once are class diagram, use case diagram and sequence diagram. You should know how to read it correctly This is not UML session… 33 [email protected]
- 35. Session-1 Class and objects Creating Classes and object Object: state, identity and behaviour Constructors: default, parameterized and copy Need of “this” , Constructor chaining Instance variable, static variable and local variable Initialization block Scanner and printf Parameter passing in Java Call by value / call by reference… 35 [email protected]
- 36. What can goes inside an class? 36 [email protected]
- 37. Creating Classes and object 37 [email protected]
- 39. Constructors: default, parameterized and copy Initialize state of the object Special method have same name as that of class Can’t return anything Can only be called once for an object Can be private Can’t be static* Can overloaded but cant overridden* Can be Default, parameterized and copy constructor 39 [email protected]
- 40. Need of this? Which id assigned to which id? “this” is an reference to the current object required to differentiate local variables with instance variables Refer next slide… 40 [email protected]
- 41. “this” used to resolve confusion… 41 [email protected]
- 42. this : Constructor chaining? Calling one constructor from another ? 42 [email protected]
- 43. Static method/variable Instance variable –per object while static variable are per class Initialize and define before any objects Most suitable for counter for object Static method can only access static data of the class For calling static method we don’t need an object of that class Now guess why main was static? 43 [email protected]
- 45. Initialization block We can put repeated constructor code in an Initialization block… Static Initialization block runs before any constructor and runs only once… 45 [email protected]
- 47. Packages Packages are Java’s way of grouping a number of related classes and/or interfaces together into a single unit. Packages act as “containers” for classes. 47 [email protected]
- 48. Java Foundation Packages Java provides a large number of classes groped into different packages based on their functionality. The six foundation Java packages are: java.lang Contains classes for primitive types, strings, math functions, threads, and exception java.util Contains classes such as vectors, hash tables, date etc. java.io Stream classes for I/O java.awt Classes for implementing GUI – windows, buttons, menus etc. java.net Classes for networking java.applet Classes for creating and implementing applets 48 [email protected]
- 49. Visibility Modifiers For instance variable and methods Public Protected Default (package level) Private For classes Public and default 49 [email protected]
- 50. Visibility Modifiers class A has default visibility hence can access in the same package only. Make class A public, then access it. Protected data can access in the same package and all the subclasses in other packages provide class itsef is public 50 [email protected]
- 51. Visibility Modifiers Accessible to: public protected Package private (default) Same Class Yes Yes Yes Yes Class in package Yes Yes Yes No Subclass in Yes Yes No No different package Non-subclass Yes No No No different package 51 [email protected]
- 52. Want to accept parameter from user? java.util.Scanner (Java 1.5) Scanner stdin = Scanner.create(System.in); int n = stdin.nextInt(); String s = stdin.next(); boolean b = stdin.hasNextInt() 52 [email protected]
- 53. Call by value Java support call by value The value changes in function is not going to reflected in the main. 53 [email protected]
- 54. Call by reference Java don’t support call by reference. When you pass an object in an method copy of reference is passed so that we can mutate the state of the object but can’t delete original object itself 54 [email protected]
- 55. Session-2 Inheritance Type of inheritance, diamond problem InstanceOf operator Final Final variable, final method , final class Acess control: public, private,protected and default Packages Abstract class Interface Polymorphism Overloading Overriding 55 [email protected]
- 56. Inheritance Inheritance is the inclusion of behaviour (i.e. methods) and state (i.e. variables) of a base class in a derived class so that they are accessible in that derived class. code reusability. Subclass and Super class concept 56 [email protected]
- 57. Diamond Problem? Hierarchy inheritance can leds to poor design.. Java don’t support it directly… ( Possible using interface ) 57 [email protected]
- 58. Inheritance example Use extends keyword Use super to pass values to base class constructor. 58 [email protected]
- 59. Overloading Overloading deals with multiple methods in the same class with the same name but different method signatures. Both the above methods have the same method names but different method signatures, which mean the methods are overloaded. Overloading lets you define the same operation in different ways for different data. Constructor can be overloaded Be careful of overloading ambiguity *Overloading in case of var-arg and Wrapper objects… 59 [email protected]
- 60. Overriding… Overriding deals with two methods, one in the parent class and the other one in the child class and has the same name and signatures. Both the above methods have the same method names and the signatures but the method in the subclass MyClass overrides the method in the superclass BaseClass Overriding lets you define the same operation in different ways for different object types. 60 [email protected]
- 61. Polymorphism Polymorphism=many forms of one things Substitutability Overriding Polymorphism means the ability of a single variable of a given type to be used to reference objects of different types, and automatically call the method that is specific to the type of object the variable references. 61 [email protected]
- 62. Polymorphism Every animal sound but differently… We want to have Pointer of Animal class assigned by object of derived class 62 [email protected]
- 64. Need of abstract class? Sound( ) method of Animal class don’t make any sense …i.e. it don’t have semantically valid definition Method sound( ) in Animal class should be abstract means incomplete Using abstract method Derivatives of Animal class forced to provide meaningful sound() method 64 [email protected]
- 65. Abstract class If an class have at least one abstract method it should be declare abstract class. Some time if we want to stop a programmer to create object of some class… Class has some default functionality that can be used as it is. Can implement only one abstract class 65 [email protected]
- 66. Abstract class use cases… Want to have some default functionality from base class and class have some abstract functionality that cant be define at that moment. Don’t want to allow a programmer to create object of an class as it is too generic Interface vs. abstract class 66 [email protected]
- 68. Final Its final: i.e. cant be change!!! final Final method arguments Cant be change inside the method Final variable Become constant, once assigned then cant be changed Final method Cant overridden Final class Cant inherited Can be reuse Some examples…. 68 [email protected]
- 69. Final class Final class cant be subclass ie cant be extended No method of this class can be overridden Ex: String class in Java… Real question is in what situation somebody should declare a class final 69 [email protected]
- 70. Final Method Final Method Can’t overridden Class containing final method can be extended Killing substitutability 70 [email protected]
- 71. Interface? Interface : contract bw two parties Interface method Only declaration, no method definition No method implementation please ! Interface variable Public static and final constant Its how java support global constant Break the hierarchy Solve diamond problem Callback in Java* Some Example …. 71 [email protected]
- 72. Interface? Rules All interface methods are always public and abstract, whether we say it or not. Variable declared inside interface are always public static and final Interface method can’t be static or final Interface cant have constructor An interface can extends other interface Can be used polymorphically An class implementing an interface must implement all of its method otherwise it need to declare abstract class… 72 [email protected]
- 74. Note Following interface constant declaration are identical int i=90; public static int i=90; public int i=90; Public static int i=90; Public static final int i=90; Following interface method declaration don’t compile final void bounce(); static void bounce(); private void bounce(); protected void bounce(); 74 [email protected]
- 75. 75 [email protected]
- 76. Type of relationship bw objects USE-A HAS-A IS-A (Most costly ? ) ALWAYS GO FOR LOOSE COUPLING AND HIGH COHESION… But HOW? 76 [email protected]
- 77. IS-A VS HAS-A 77 [email protected]
- 78. Self Reading ..will discuss latter.. Implementation inheritance (Already done) Interface inheritance with composition(Google it) 78 [email protected]
- 81. Session-1 String class Immutability and usages, stringbuilder and stringbuffer Wrapper classes and usages Java 5 Language Features (I): AutoBoxing and Unboxing Enhanced For loop Varargs Static Import Enums Inner classes Regular inner class method local inner class anonymous inner class 81 [email protected]
- 82. String Immutable i.e. once assigned then can’t be changed Only class in java for which object can be created with or without using new operator Ex: String s=“india”; String s1=new String(“india”); What is the difference? String concatenation can be in two ways: String s1=s+”paki”; Operator overloading String s3=s1.concat(“paki”); 82 [email protected]
- 83. Some common string methods… charAt() Returns the character located at the specified index concat() Appends one String to the end of another ( "+" also works) equalsIgnoreCase() Determines the equality of two Strings, ignoring case length() Returns the number of characters in a String replace() Replaces occurrences of a character with a new character substring() Returns a part of a String toLowerCase() Returns a String with uppercase characters converted toString() Returns the value of a String toUpperCase() Returns a String with lowercase characters converted trim() Removes whitespace from the ends of a String 83 [email protected]
- 84. String comparison Two string should never be checked for equality using == operator WHY? Always use equals( ) method…. String s1=“india”; String s2=“paki”; if(s1.equals(s2)) ….. ….. 84 [email protected]
- 85. Immutability Immutability means something that cannot be changed. Strings are immutable in Java. What does this mean? String literals are very heavily used in applications and they also occupy a lot of memory. Therefore for efficient memory management, all the strings are created and kept by the JVM in a place called string pool (which is part of Method Area). Garbage collector does not come into string pool. How does this save memory? 85 [email protected]
- 86. Wrapper classes Helps treating primitive data as an object But why we should convert primitive to objects? We can’t store primitive in java collections Object have properties and methods Have different behavior when passing as method argument Eight wrapper for eight primitive Integer, Float, Double, Character, Boolean etc… Integer it=new Integer(33); int temp=it.intValue(); …. 86 [email protected]
- 87. Boxing / Unboxing Java 1.5 Boxing ----------- Integer iWrapper = 10; Prior to J2SE 5.0, we use Integer a = new Integer(10); Unboxing ------------- int iPrimitive = iWrapper; Prior to J2SE 5.0, we use int b = iWrapper.intValue(); 87 [email protected]
- 88. Java 5 Language Features (I) AutoBoxing and Unboxing Enhanced For loop Varargs Static Import Enums 88 [email protected]
- 89. Enhanced For loop Provide easy looping construct to loop through array and collections 89 [email protected]
- 90. Varargs Java start supporting variable argument method in Java 1.5 Discuss function overloading in case of Varargs and wrapper classes 90 [email protected]
- 91. Static Import Handy feature in Java 1.5 that allow something like this: import static java.lang.Math.PI; import static java.lang.Math.cos; Now rather then using double r = Math.cos(Math.PI * theta); We can use something like double r = cos(PI * theta); – looks more readable …. Avoid abusing static import like import static java.lang.Math.*; General guidelines to use static java import: 1) Use it to declare local copies of java constants 2) When you require frequent access to static members from one or two java classes 91 [email protected]
- 92. Enums Enum is a special type of classes. enum type used to put restriction on the instance values 92 [email protected]
- 93. Inner classes A class define inside another Why to define it? 93 [email protected]
- 94. top level inner class Non static inner class object can't be createed without outer class instance All the private data of outer class is available to inner class Non static inner class can't have static members 94 [email protected]
- 95. Method local inner class Class define inside an method Can not access local data define inside method Declare local data static to access it 95 [email protected]
- 96. Anonymous Inner class A way to implement polymorphism “On the fly” 96 [email protected]
- 97. Session-2 Exception handling Try, catch, throw, throws, finally Checked and Unchecked exception User defined exceptions assertions 97 [email protected]
- 98. What is Exception? An exception is an abnormal condition that arises while running a program. Examples: Attempt to divide an integer by zero causes an exception to be thrown at run time. Attempt to call a method using a reference that is null. Attempting to open a nonexistent file for reading. JVM running out of memory. Exception handling do not correct abnormal condition rather it make our program robust i.e. make us enable to take remedial action when exception occurs…Help in recovering… 98 [email protected]
- 99. Type of exceptions RuntimeEx: Unchecked Exception CompiletimeEx: Checked Error: Should not to be handled by programmer..like JVM crash all problem happens at run time in programming and also in real life..... for checked ex, we need to tell java we know about those problems for example readLine() throws IOException 99 [email protected]
- 101. Exceptions and their Handling When the JVM encounters an error such as divide by zero, it creates an exception object and throws it – as a notification that an error has occurred. If the exception object is not caught and handled properly, the interpreter will display an error and terminate the program. If we want the program to continue with execution of the remaining code, then we should try to catch the exception object thrown by the error condition and then take appropriate corrective actions. This task is known as exception handling. 101 [email protected]
- 102. Common Java Exceptions ArithmeticException ArrayIndexOutOfBoundException ArrayStoreException FileNotFoundException IOException – general I/O failure NullPointerException – referencing a null object OutOfMemoryException SecurityException – when applet tries to perform an action not allowed by the browser’s security setting. StackOverflowException StringIndexOutOfBoundException 102 [email protected]
- 103. design by contract? Design by contract specifies the obligations of a calling- method and called-method to each other. Valuable technique to have well designed interface Help programmer clearly to think what a function does and what are pre and post condition that must satisfied. Java uses the assert statement to implement pre- and post-conditions. Java’s exceptions handling also support design by contract especially checked exceptions 103 [email protected]
- 104. Preconditions Contract the calling-method must agree to. Conditions that must be true before a called method can execute. Preconditions involve the system state and the arguments passed into the method at the time of its invocation. If a precondition fails then there is a bug in the calling-method or calling software component. Post conditions contract the called-method agrees to. What must be true after a method completes successfully. Post conditions can be used with assertions in both public and non-public methods. The post conditions involve the old system state, the new system state, the method arguments and the method’s return value. If a post condition fails then there is a bug in the called-method or called software component. 104 [email protected]
- 107. Class invariants what must be true about each instance of a class? A class invariant as an internal invariant that can specify the relationships among multiple attributes, and should be true before and after any method completes. If an invariant fails then there could be a bug in either calling-method or called- method. It is convenient to combine all the expressions required for checking invariants into a single internal method that can be called by assertions. For example if you have a class, which deals with negative integers then you define the isNegative() convenient internal method 107 [email protected]
- 109. Session-1 Char and byte oriented streams BufferedReader and BufferedWriter File handling Object Serialization [ObjectInputStream / ObjectOutputStream] 109 [email protected]
- 110. Stream Stream is an abstraction that either produces or consumes information. A stream is linked to a physical device by the Java I/O system. All streams behave in the same manner, even if the actual physical devices to which they are linked differ. 2 types of streams: byte : for binray data All byte stream class are like XXXXXXXXStream character: for text data All char stream class are like XXXXXXXXReader/ XXXXXXWriter 110 [email protected]
- 111. 111 [email protected]
- 112. Some important classes form java.io 112 [email protected]
- 113. System class in java System class defined in java.lang package It encapsulate many aspect of JRE System class also contain 3 predefine stream variables in System.in (InputStream) Out System.out(PrintStream) Err System.err(console) 113 [email protected]
- 114. BufferedReader and BufferedWriter Reading form console BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); Reading form file BufferedReader br=new BufferedReader(new InputStreamReader(new File(“foo.txt”))); 114 [email protected]
- 115. File File abstraction that FileReader represent file and char[] in = new char[50]; // to store input directories int size = 0; FileReader fr =new FileReader(file); File f=new File("...."); boolean flag= file.createNewFile(); size = fr.read(in); // read the whole file! boolean flag= file.mkDir(); System.out.print(size + " "); // how many bytes read boolean flag=file.exists(); FileWriter for(char c : in) // print the array System.out.print(c); File file = new File( "fileWrite2.txt"); FileWriter fw =new FileWriter(file); fr.close(); // again, always close fw.write("howdynfolksn"); // write characters to fw.flush(); // flush before closing fw.close(); // close file when done 115 [email protected]
- 116. Serialization Storing the state of the object on a file along some metadata….so that it Can be recovered back……….. Serialization used in RMI (Remote method invocation ) while sending an object from one place to another in network… 116 [email protected]
- 117. What actually happens during Serialization The state of the object from heap is sucked and written along with some meta data in an file…. 117 [email protected]
- 118. De- Serialization When an object is de-serialized, the JVM attempts to bring object back to the life by making an new object on the heap that have the same state as original object Transient variable don’t get saved during serialization hence come with null !!! 118 [email protected]
- 120. Session-2 Multi-Threading Creating threads: using Thread class and Runnable interface Thread life cycle Using sleep(), join(), thread priorities Synchronization Solving producer and consumer problem using wait() and notify() Deadlock introduction 120 [email protected]
- 121. What is threads? LWP 121 [email protected]
- 122. Basic fundamentals Thread: class in java.lang thread: separate thread of execution What happens during multithreading? 1. JVM calls main() method 2. main() starts a new thread. Main thread is tempory frozen while new thread start running so JVM switch between created thread and main thread till both complets 122 [email protected]
- 123. Creating threads in Java? Implements Runnable interface Extending Thread class…….. Job and Worker analogy… 123 [email protected]
- 124. Thread life cycle… If a thread is blocked ( put to sleep) specified no of ms should expire If thread waiting for IO that must be over.. If a thred calls wait() then another thread must call notify() or notifyAll() If an thred is suspended() some one must call resume() 124 [email protected]
- 125. Java.lang.Thread Thread() construct new thread void run() must be overriden void start() start thread call run method static void sleep(long ms) put currently executing thread to sleep for specified no of millisecond boolean isAlive() return true if thread is started but not expired void stop() void suspend() and void resume() Suspend thread execution…. 125 [email protected]
- 126. Java.lang.Thread void join(long ms) Main thread Wait for specified thread to complete or till specified time is not over void join() Main thread Wait for specified thread to complete static boolean interrupted() boolean inInterrupted() void interrupt() Send interrupt request to a thread 126 [email protected]
- 127. Creating Threads By extending Thread class Implementing the Runnable interface 127 [email protected]
- 131. Synchronization Synchronization Mechanism to controls the order in which threads execute Competition vs. cooperative synchronization Mutual exclusion of threads Each synchronized method or statement is guarded by an object. When entering a synchronized method or statement, the object will be locked until the method is finished. When the object is locked by another thread, the current thread must wait. [email protected] 131
- 133. Inter thread communication Java have elegant Interprocess communication using wait() notify() and notifyAll() methods All these method defined final in the Object class Can be only called from a synchronized context 133 [email protected]
- 134. wait() and notify(), notifyAll() wait() Tells the calling thread to give up the monitor and go to the sleep until some other thread enter the same monitor and call notify() notify() Wakes up the first thread that called wait() on same object notifyAll() Wakes up all the thread that called wait() on same object, highest priority thread is going to run first 134 [email protected]
- 135. Incorrect implementation of produce consumer … 135 [email protected]
- 136. Correct implementation of produce consumer … 136 [email protected]
- 138. Session-1 Session-1 Object class in Java Collections Framework List, Map, Set usages introduction Usages ArrayList, LinkedList, HashMap, TreeMap, HashSet Comparable, Comparator interface implementation User define key in HashMap 138 [email protected]
- 139. Object Object is an special class in java defined in java.lang Every class automatically inherit this class whether we say it or not… Why Java has provided this class? 139 [email protected]
- 140. Method defined in Object class… String toString() boolean equals() int hashCode() clone() void finalize() getClass() Method that can’t be overridden final void notify() final void notifyAll() final void wait() 140 [email protected]
- 141. toString( ) If we don’t overriding toString() method of Object class it print Object ID no by default Override it to print some useful information…. 141 [email protected]
- 143. equals What O/P do you expect in this case…… O/P would be two employees are not equals.... ??? Problem is that using == java compare object id of two object and that can never be equals, so we are getting meaningless result… 143 [email protected]
- 144. Overriding equals() Don’t forget DRY run….. 144 [email protected]
- 145. hashCode() Whenever you override equals()for an type don’t forget to override hashCode() method… hashCode() make DS efficient What hashCode does HashCode divide data into buckets Equals search data from that bucket… 145 [email protected]
- 146. clone() Lets consider an object that creation is very complicated, what we can do we can make an clone of that object and use that Costly , avoid using cloning if possible, internally depends on serialization Must make class supporting cloning by implementing an marker interface ie Cloneable 146 [email protected]
- 147. finalize() As you are aware ..Java don’t support destructor Programmer is free from memory management Memory mgt is done by an component of JVM ie called Garbage collector GC GC runs as low priority thread.. We can override finalize() to request java “Please run this code before recycling this object” Cleanup code can be written Not reliable, better not to use… Demo programm WAP to count total number of employee object in the memory at any moment of time if an object is nullified then reduce count…. 147 [email protected]
- 148. Java collection Java collections can be considered a kind of readymade data structure, we should only need to know how to use them and how they work…. collection Name of topic Collection Base interface Collections Static utility class provide various useful algorith 148 [email protected]
- 149. collection Collection Why it is called an framework? Readymade Data structure in Java… 149 [email protected]
- 150. 150 [email protected]
- 151. ArrayList: aka growable array… 151 [email protected]
- 152. ArrayList of user defined object 152 [email protected]
- 153. Comparable and Comparator interface We need to teach Java how to sort user define object Comparable and Comparator interface help us to tell java how to sort user define object…. 153 [email protected]
- 155. Comparator Don’t need to change Employee class 155 [email protected]
- 159. LinkedList : AKA Doubly Link list……….. can move back and forth....... 159 [email protected]
- 161. fundamental diff bw ArrayList and LinkedList ArrayLists manage arrays internally. [0][1][2][3][4][5] .... List<Integer> arrayList = new ArrayList<Integer>(); LinkedLists consists of elements where each element has a reference to the previous and next element [0]->[1]->[2] .... <- <- 161 [email protected]
- 162. ArrayList vs LinkedList Java implements ArrayList as array internally Hence good to provide starting size i.e. List<String> s=new ArrayList<String>(20); is better then List<String> s=new ArrayList<String>(); Removing element from starting of arraylist is very slow? list.remove(0); if u remove first element, java internally copy all the element (shift by one) Adding element at middle in ArrayList is very inefficient… 162 [email protected]
- 163. Performance ArrayList vs LinkedList !!! 163 [email protected]
- 164. HashMap Key ---->Value declaring an hashmap HashMap<Integer, String> map = new HashMap<Integer, String>(); populating values map.put(5, "Five"); map.put(8, "Eight"); map.put(6, "Six"); map.put(4, "Four"); map.put(2, "Two"); getting value String text = map.get(6); System.out.println(text); 164 [email protected]
- 165. Looping through HashMap for(Integer key: map.keySet()) { String value = map.get(key); System.out.println(key + ": " + value); } 165 [email protected]
- 166. LinkedHashMap aka dll key and value are in same order in which u hv inserted....... TreeMap sort keys in natural order(what is natural order?) for int 1,2,3.......... for string "a","b"............. For user define key Define sorting order using Comparable /Comparator 166 [email protected]
- 167. set Don’t allow duplicate element 167 [email protected]
- 169. User define key in HashMap If you are using user define key in hashmap don’t forget to override hashcode for that class… otherwise you may not find that content again… Demo 169 [email protected]
- 170. HashMap vs Hashtable Hashtable is threadsafe, slow as compared to HashMap Better to use HashMap Some more intresting difference Hashtable give runtime exception if key is “null” while HashMap don’t 170 [email protected]
- 171. Session-2 Java 5 Language Features II Generics Annotations 171 [email protected]
- 172. Generics Before Java 1.5 List list=new ArrayList(); Can add anything in that list Problem while retrieving Now Java 1.5 onward List<String> list=new ArrayList<String>(); list.add(“foo”);//ok list.add(22);// compile time error Generics provide type safety Generics is compile time phenomena… 172 [email protected]
- 173. Issues with Generics Try not to mix non Generics code and Generics code…we can have strange behaviour. 173 [email protected]
- 179. Annotation @ magic !!! Annotations in Java is all about adding meta-data facility to the Java Elements. Like Classes, Interfaces or Enums, Annotations define a type in Java and they can be applied to several Java Elements. Tools which will read and interpret the Annotations will implement a lot of functionalities from the meta-information obtained. For example, they can ensure the consistency between classes, can check the validity of the paramters passed by the clients at run-time and can generate lot of base code for a project. 179 [email protected]
- 180. Built-in Annotations in Java There are some pre-defined annotations available in the Java Programming language. They are, Override Deprecated SuppressWarnings Demo user define annotation and its need… 180 [email protected]
- 181. References:- Head first java SCJP katthy Google Stackoverflow.com ….. ….. 181 [email protected]