Objectoriented Programming in Java Session 11 Design Patterns
Object-oriented Programming in Java Session: 11 Design Patterns
Objectives u u u Describe polymorphism Describe the procedure to override methods of the Object class Explain design patterns Describe the Singleton, Data Access Object (DAO), and Factory and Observer design patterns Describe delegation Explain composition and aggregation © Aptech Ltd. Design Patterns/Session 11 2
Introduction u u The concept of polymorphism can be applied to Java. In Java, a subclass can have its own unique behavior even while sharing certain common functionalities with the parent class. © Aptech Ltd. Design Patterns/Session 11 3
![Implementing Polymorphism [1 -4] u u A super class named Car has been created](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-4.jpg "Implementing Polymorphism [1 -4] u u A super class named Car has been created")
Implementing Polymorphism [1 -4] u u A super class named Car has been created having two methods, accelerate() and print. Description(). A sub class named Luxury. Car is created based on Car and overrides the methods of the Car class. Code Snippet class Luxury. Car extends Car { // Luxury. Car defines an additional feature named perks public String perks; public Luxury. Car(int mileage, String color, String make, String perks) { super(mileage, color, make); this. perks = perks; } © Aptech Ltd. Design Patterns/Session 11 4
![Implementing Polymorphism [2 -4] public void accelerate() { System. out. println(“Luxury Car is Accelerating”);](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-5.jpg "Implementing Polymorphism [2 -4] public void accelerate() { System. out. println(“Luxury Car is Accelerating”);")
Implementing Polymorphism [2 -4] public void accelerate() { System. out. println(“Luxury Car is Accelerating”); } public void print. Description() { super. print. Description(); System. out. println(“The “ + “Luxury car is a: “ + this. perks + “. ”); } } © Aptech Ltd. Design Patterns/Session 11 5
![Implementing Polymorphism [3 -4] Code Snippet 2 creates two instances of type Car, instantiates](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-6.jpg "Implementing Polymorphism [3 -4] Code Snippet 2 creates two instances of type Car, instantiates")
Implementing Polymorphism [3 -4] Code Snippet 2 creates two instances of type Car, instantiates them, and invokes the accelerate() and print. Description() methods on each instance respectively. Code Snippet public class Polymorphism. Test { /** * @param args the command line arguments */ public static void main(String[] args) { Car obj. Car, obj. Luxury. Car; obj. Car = new Car(80, “Red”, “BMW”); obj. Luxury. Car = new Luxury. Car(120, “Yellow”, “Ferrari”, “Sports Car”); © Aptech Ltd. Design Patterns/Session 11 6
![Implementing Polymorphism [4 -4] obj. Car. accelerate(); obj. Car. print. Description(); //System. out. println(“Now](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-7.jpg "Implementing Polymorphism [4 -4] obj. Car. accelerate(); obj. Car. print. Description(); //System. out. println(“Now")
Implementing Polymorphism [4 -4] obj. Car. accelerate(); obj. Car. print. Description(); //System. out. println(“Now inside Luxury. Car”); obj. Luxury. Car. accelerate(); obj. Luxury. Car. print. Description(); } } © Aptech Ltd. Design Patterns/Session 11 7
![Overriding the Methods of Object Class [1 -12] u u u Object is the](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-8.jpg "Overriding the Methods of Object Class [1 -12] u u u Object is the")
Overriding the Methods of Object Class [1 -12] u u u Object is the root class. Its methods can be overridden by any class (unless the methods are marked as final). Following are the methods that can be overridden with a different functionality as compared to the root class: ² ² ² u u The equals() method compares two objects to determine if they are equal. There are two different types of equality. They are: ² ² u u public boolean equals(Object obj) public int hash. Code() public String to. String() Reference equality Logical equality Reference equality is when the physical memory locations of the two strings are same. Logical equality is when data in the objects are the same. © Aptech Ltd. Design Patterns/Session 11 8
![Overriding the Methods of Object Class [2 -12] Code Snippet public class Equality. Test](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-9.jpg "Overriding the Methods of Object Class [2 -12] Code Snippet public class Equality. Test")
Overriding the Methods of Object Class [2 -12] Code Snippet public class Equality. Test { /** * @param args the command line arguments */ public static void main(String[] args) { String str. AObj = new String(“JOHN”); String str. BObj = new String(“JOHN”); String str. CObj = new String(“ANNA”); String str. EObj = str. AObj; System. out. println(str. AObj == str. BObj); System. out. println(str. AObj == str. CObj); System. out. println(str. AObj == str. EObj); } } © Aptech Ltd. Design Patterns/Session 11 9
![Overriding the Methods of Object Class [3 -12] u u u The equality operator](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-10.jpg "Overriding the Methods of Object Class [3 -12] u u u The equality operator")
Overriding the Methods of Object Class [3 -12] u u u The equality operator (==) compares the memory addresses of the two strings. When str. AObj is compared to str. BObj, the result is false, although their value is same, which is JOHN. A comparison between str. AObj and str. CObj returns false because the references of the two different String objects are different addresses. When str. AObj is compared to str. EObj, the result is true because they point to the same memory location. The Code Snippet displays the following output: © Aptech Ltd. Design Patterns/Session 11 10
![Overriding the Methods of Object Class [4 -12] Code Snippet public class Logical. Equality.](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-11.jpg "Overriding the Methods of Object Class [4 -12] Code Snippet public class Logical. Equality.")
Overriding the Methods of Object Class [4 -12] Code Snippet public class Logical. Equality. Test { /** * @param args the command line arguments */ public static void main(String[] args) { // TODO code application logic here String str. AObj = new String(“JOHN”); String str. BObj = new String(“JOHN”); String str. CObj = new String(“ANNA”); // Create a String reference and assign an existing // String’s reference // to it so that both references point to the same // String object in memory. String str. EObj = str. AObj; © Aptech Ltd. Design Patterns/Session 11 11
![Overriding the Methods of Object Class [5 -12] // Print the results of the](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-12.jpg "Overriding the Methods of Object Class [5 -12] // Print the results of the")
Overriding the Methods of Object Class [5 -12] // Print the results of the equality checks System. out. println(“===============”); System. out. println(“Logical or Value Equality”); System. out. println(“===============”); //Tests logical or value equality System. out. println(str. AObj. equals(str. BObj)); System. out. println(str. AObj. equals(str. CObj)); System. out. println(str. AObj. equals(str. EObj)); } } © Aptech Ltd. Design Patterns/Session 11 12
![Overriding the Methods of Object Class [6 -12] u u The equals() method is](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-13.jpg "Overriding the Methods of Object Class [6 -12] u u The equals() method is")
Overriding the Methods of Object Class [6 -12] u u The equals() method is used to check for logical equality. Note that the equals() method is implicitly inherited from the Object class. The String class overrides the equals() method and compares the two String objects character by character. The Code Snippet displays the following output: © Aptech Ltd. Design Patterns/Session 11 13
![Overriding the Methods of Object Class [7 -12] u u u The hash. Code()](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-14.jpg "Overriding the Methods of Object Class [7 -12] u u u The hash. Code()")
Overriding the Methods of Object Class [7 -12] u u u The hash. Code() method of Object class returns the object’s memory address in hexadecimal format. It is used along with the equals() method in hash-based collections such as Hashtable. If two objects are equal, their hash code should also be equal. Code Snippet public class Student { private int ID; public int get. ID() { Scanner sc = new Scanner(System. in); System. out. println(“Enter values”); int ID = Integer. parse. Int(sc. next. Line()); return ID; } © Aptech Ltd. Design Patterns/Session 11 14
![Overriding the Methods of Object Class [8 -12] public boolean equals(Object obj) { if](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-15.jpg "Overriding the Methods of Object Class [8 -12] public boolean equals(Object obj) { if")
Overriding the Methods of Object Class [8 -12] public boolean equals(Object obj) { if (get. ID() == ((Student)obj). get. ID()) return true; else return false; } public int hash. Code() { return ID; } /** * @param args the command line arguments */ © Aptech Ltd. Design Patterns/Session 11 15
![Overriding the Methods of Object Class [9 -12] public static void main(String[] args) {](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-16.jpg "Overriding the Methods of Object Class [9 -12] public static void main(String[] args) {")
Overriding the Methods of Object Class [9 -12] public static void main(String[] args) { Student s 1 = new Student(); Student s 2 = new Student(); if (s 1. equals(s 2)) System. out. println(“The two ID values are equal”); else System. out. println(“The two ID values are not equal”); } } © Aptech Ltd. Design Patterns/Session 11 16
![Overriding the Methods of Object Class [10 -12] u u u u The Student](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-17.jpg "Overriding the Methods of Object Class [10 -12] u u u u The Student")
Overriding the Methods of Object Class [10 -12] u u u u The Student class defines three methods in addition to main() method. The get. ID() method accepts an ID value from the standard input. The overridden equals() method accepts a parameter of type Object. It compares the ID value of this object with the ID value of the current object. The overridden hash. Code() method returns the ID value. In the main() method, two objects of Student class, namely, s 1 and s 2 are created. The equals() method is invoked on s 1 and the object s 2 is passed as a parameter. Depending on the user input, the output will be displayed accordingly. © Aptech Ltd. Design Patterns/Session 11 17
![Overriding the Methods of Object Class [11 -12] u u The to. String() method](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-18.jpg "Overriding the Methods of Object Class [11 -12] u u The to. String() method")
Overriding the Methods of Object Class [11 -12] u u The to. String() method of Object class returns a string representation of the object. It is typically used for debugging. Code Snippet public class Exponent { private double num, exp; public Exponent(double num, double exp) { this. num = num; this. exp = exp; } /* Returns the string representation of this number. The format of string is “Number + e Value” where Number is the number value and e Value is the exponent part. © Aptech Ltd. Design Patterns/Session 11 18
![Overriding the Methods of Object Class [12 -12] @Override public String to. String() {](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-19.jpg "Overriding the Methods of Object Class [12 -12] @Override public String to. String() {")
Overriding the Methods of Object Class [12 -12] @Override public String to. String() { return String. format(num + “E+” + exp); } /** * @param args the command line arguments */ public static void main(String[] args) { Exponent c 1 = new Exponent(10, 15); System. out. println(c 1); } } © Aptech Ltd. Design Patterns/Session 11 19
![The instanceof Operator [1 -5] u The instanceof operator is used to compare an](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-20.jpg "The instanceof Operator [1 -5] u The instanceof operator is used to compare an")
The instanceof Operator [1 -5] u The instanceof operator is used to compare an object to a specified type such as instance of a class and an instance of a subclass. Code Snippet class Employee { int empcode; String name; String dept; int bonus; } class Manager extends Employee { String name; int mgrid; } © Aptech Ltd. Design Patterns/Session 11 20
![The instanceof Operator [2 -5] public class Square { /** * @param args the](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-21.jpg "The instanceof Operator [2 -5] public class Square { /** * @param args the")
The instanceof Operator [2 -5] public class Square { /** * @param args the command line arguments */ public static void main(String[] args) { Employee emp 1 = new Employee(); Scanner sc = new Scanner(System. in); System. out. println(“Enter values”); emp 1. name = sc. next. Line(); Employee m 1 = new Manager(); m 1. name = sc. next. Line(); if (emp 1 instanceof Employee) { emp 1. bonus = 7000; System. out. println(emp 1. name + “ is an employee and has bonus “+emp 1. bonus); © Aptech Ltd. Design Patterns/Session 11 21
![The instanceof Operator [3 -5] if (emp 1 instanceof Manager) { emp 1. bonus](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-22.jpg "The instanceof Operator [3 -5] if (emp 1 instanceof Manager) { emp 1. bonus")
The instanceof Operator [3 -5] if (emp 1 instanceof Manager) { emp 1. bonus = 12000; System. out. println(emp 1. name + “ is a manager and has bonus “+emp 1. bonus); } if (m 1 instanceof Employee) { m 1. bonus = 7000; System. out. println(m 1. name + “ is an employee and has bonus “+ m 1. bonus); } © Aptech Ltd. Design Patterns/Session 11 22
![The instanceof Operator [4 -5] if (m 1 instanceof Manager) { m 1. bonus](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-23.jpg "The instanceof Operator [4 -5] if (m 1 instanceof Manager) { m 1. bonus")
The instanceof Operator [4 -5] if (m 1 instanceof Manager) { m 1. bonus = 12000; System. out. println(m 1. name + “ is a manager and has bonus “+ m 1. bonus); } } } © Aptech Ltd. Design Patterns/Session 11 23
![The instanceof Operator [5 -5] u The code defines the following: ² ² u](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-24.jpg "The instanceof Operator [5 -5] u The code defines the following: ² ² u")
The instanceof Operator [5 -5] u The code defines the following: ² ² u Parent class, Employee Child class, Manager that inherits from the parent The following displays the output of the code: © Aptech Ltd. Design Patterns/Session 11 24
![Design Patterns [1 -10] u u u A design pattern is a clearly defined](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-25.jpg "Design Patterns [1 -10] u u u A design pattern is a clearly defined")
Design Patterns [1 -10] u u u A design pattern is a clearly defined solution to problems that occur frequently. Design pattern are based on the fundamental principles of object oriented design. Following are the different types of design patterns: ² ² ² u u Creational Patterns Structural Patterns Behavioral Patterns Singleton pattern is a type of creational pattern. The singleton design pattern provides complete information on such class implementations. © Aptech Ltd. Design Patterns/Session 11 25
![Design Patterns [2 -10] u Consider the following when implementing the singleton design pattern:](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-26.jpg "Design Patterns [2 -10] u Consider the following when implementing the singleton design pattern:")
Design Patterns [2 -10] u Consider the following when implementing the singleton design pattern: ² ² ² © Aptech Ltd. The reference is finalized so that it does not reference a different instance. The private modifier allows only same class access and restricts attempts to instantiate the singleton class. The factory method provides greater flexibility. It is commonly used in singleton implementations. The singleton class usually includes a private constructor that prevents a constructor to instantiate the singleton class. To avoid using the factory method, a public variable can be used at the time of using a static reference. Design Patterns/Session 11 26
![Design Patterns [3 -10] Code Snippet class Singleton. Example { private static Singleton. Example](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-27.jpg "Design Patterns [3 -10] Code Snippet class Singleton. Example { private static Singleton. Example")
Design Patterns [3 -10] Code Snippet class Singleton. Example { private static Singleton. Example singleton. Example = null; private Singleton. Example() { } public static Singleton. Example get. Instance() { if (singleton. Example == null) { singleton. Example = new Singleton. Example(); } return singleton. Example; } public void display() { System. out. println(“Welcome to Singleton Design Pattern”); } } © Aptech Ltd. Design Patterns/Session 11 27
![Design Patterns [4 -10] u u The Singleton. Example class contains a private static](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-28.jpg "Design Patterns [4 -10] u u The Singleton. Example class contains a private static")
Design Patterns [4 -10] u u The Singleton. Example class contains a private static Singleton. Example field. There is a private constructor. The public static get. Instance() method returns the only Singleton. Example instance. There is a public say. Hello() method that can test the singleton. © Aptech Ltd. Design Patterns/Session 11 28
![Design Patterns [5 -10] Code Snippet public class Singleton. Test { /** * @param](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-29.jpg "Design Patterns [5 -10] Code Snippet public class Singleton. Test { /** * @param")
Design Patterns [5 -10] Code Snippet public class Singleton. Test { /** * @param args the command line arguments */ public static void main(String[] args) { Singleton. Example singleton. Example = Singleton. Example. get. Instance(); singleton. Example. display(); } } u u The display() method is called on the singleton class. The output of the program is “Welcome to Singleton Design Pattern”. © Aptech Ltd. Design Patterns/Session 11 29
![Design Patterns [6 -10] u u In Java, interfaces include constant fields. They can](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-30.jpg "Design Patterns [6 -10] u u In Java, interfaces include constant fields. They can")
Design Patterns [6 -10] u u In Java, interfaces include constant fields. They can be used as reference types. They are important components of many design patterns. An interface declaration includes the following: ² ² ² © Aptech Ltd. Modifiers The keyword interface The interface name A comma-separated list of parent interfaces that it can extend The interface body Design Patterns/Session 11 30
![Design Patterns [7 -10] u u u The Data Access Object (DAO) pattern is](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-31.jpg "Design Patterns [7 -10] u u u The Data Access Object (DAO) pattern is")
Design Patterns [7 -10] u u u The Data Access Object (DAO) pattern is used when an application is created that needs to persist its data. The DAO pattern involves a technique for separating the business logic from persistence logic. The DAO pattern uses the following: ² ² ² © Aptech Ltd. DAO Interface DAO Concrete Class Model Object or Value Object Design Patterns/Session 11 31
![Design Patterns [8 -10] The following figure shows the structure of a DAO design](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-32.jpg "Design Patterns [8 -10] The following figure shows the structure of a DAO design")
Design Patterns [8 -10] The following figure shows the structure of a DAO design pattern: © Aptech Ltd. Design Patterns/Session 11 32
![Design Patterns [9 -10] Factory Pattern: u It is one of the commonly used](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-33.jpg "Design Patterns [9 -10] Factory Pattern: u It is one of the commonly used")
Design Patterns [9 -10] Factory Pattern: u It is one of the commonly used design patterns in Java. u It belongs to the creational pattern category. u This pattern does not perform direct constructor calls when invoking a method. Observer Pattern: u This helps to observe the behavior of objects such as change in state or change in property. u Here, an object called the subject maintains a collection of objects called observers. u Whenever the subject changes, it notifies the observers. u Observers can be added or removed from the collection of observers in the subject. © Aptech Ltd. Design Patterns/Session 11 33
![Design Patterns [10 -10] The following figure shows the factory pattern diagram: © Aptech](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-34.jpg "Design Patterns [10 -10] The following figure shows the factory pattern diagram: © Aptech")
Design Patterns [10 -10] The following figure shows the factory pattern diagram: © Aptech Ltd. Design Patterns/Session 11 34
Delegation u u u Delegation is a relationship between objects. Here, one object forwards method calls to another object, which is called its delegate. Unlike inheritance, delegation does not create a super class. Delegation does not force to accept all the methods of the super class. Delegation supports code reusability and provides run-time flexibility. © Aptech Ltd. Design Patterns/Session 11 35
![Composition and Aggregation [1 -6] u u u Composition refers to the process of](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-36.jpg "Composition and Aggregation [1 -6] u u u Composition refers to the process of")
Composition and Aggregation [1 -6] u u u Composition refers to the process of composing a class from references to other objects. Composition forms the building blocks for data structures. Programmers can use object composition to create more complex objects. In aggregation, one class owns another class. In composition, when the owning object is destroyed, so are the objects within it but in aggregation, this is not true. Composition and aggregation are design concepts and not actual patterns. © Aptech Ltd. Design Patterns/Session 11 36
![Composition and Aggregation [2 -6] Code Snippet // Composition class House { // House](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-37.jpg "Composition and Aggregation [2 -6] Code Snippet // Composition class House { // House")
Composition and Aggregation [2 -6] Code Snippet // Composition class House { // House has door. // Door is built when House is built, // it is destroyed when House is destroyed. private Door dr; }; To implement object composition, perform the following steps: ² ² © Aptech Ltd. Create a class with reference to other classes. Add the same signature methods that forward to the referenced object. Design Patterns/Session 11 37
![Composition and Aggregation [3 -6] u Consider an example of a student attending a](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-38.jpg "Composition and Aggregation [3 -6] u Consider an example of a student attending a")
Composition and Aggregation [3 -6] u Consider an example of a student attending a course. ² ² The student ‘has a’ course. The composition for the Student and Course classes is depicted in the following Code Snippet: Code Snippet package composition; public class Course { private String title; private long score; private int id; public String get. Title() { return title; } © Aptech Ltd. Design Patterns/Session 11 38
![Composition and Aggregation [4 -6] public void set. Title(String title) { this. title =](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-39.jpg "Composition and Aggregation [4 -6] public void set. Title(String title) { this. title =")
Composition and Aggregation [4 -6] public void set. Title(String title) { this. title = title; } public long get. Score() { return score; } public void set. Score(long score) { this. score = score; } public int get. Id() { return id; } public void set. Id(int id) { this. id = id; } } © Aptech Ltd. Design Patterns/Session 11 39
![Composition and Aggregation [5 -6] package composition; public class Student { //composition has-a relationship](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-40.jpg "Composition and Aggregation [5 -6] package composition; public class Student { //composition has-a relationship")
Composition and Aggregation [5 -6] package composition; public class Student { //composition has-a relationship private Course course; public Student(){ this. course=new Course(); course. set. Score(1000); } public long get. Score() { return course. get. Score(); } /** * @param args the command line arguments */ © Aptech Ltd. Design Patterns/Session 11 40
![Composition and Aggregation [6 -6] public static void main(String[] args) { Student p =](http://slidetodoc.com/presentation_image_h/25b2dab0871d5eddc217b8a44f602195/image-41.jpg "Composition and Aggregation [6 -6] public static void main(String[] args) { Student p =")
Composition and Aggregation [6 -6] public static void main(String[] args) { Student p = new Student(); System. out. println(p. get. Score()); } } © Aptech Ltd. Design Patterns/Session 11 41
Summary u u u u The development of application software is performed using a programming language that enforces a particular style of programming, also referred to as programming paradigm. In structured programming paradigm, the application development is decomposed into a hierarchy of subprograms. In object-oriented programming paradigm, applications are designed around data, rather than focusing only on the functionalities. The main building blocks of an OOP language are classes and objects. An object represents a real-world entity and a class is a conceptual model. Java is an OOP language as well a platform used for developing applications that can be executed on different platforms. Java platform is a software-only platform that runs on top of the other hardware-based platforms. The editions of Java platform are Java SE, Java EE, and Java ME. The components of Java SE platform are JDK and JRE provides JVM and Java libraries that are used to run a Java program. JDK includes the necessary development tools, runtime environment, and APIs for creating Java programs. © Aptech Ltd. Design Patterns/Session 11 42
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