Advanced technology has taken a prominent place in everyone's life. We can't live without technology, be it for day-to-day tasks or at the office. Design Pattern is one such technology developers use. Design patterns represent the best practices used by experienced Object-oriented software developers and professionals who work day and night to identify the code, decode it as per the needs and wants, identify the problems, and bring in solutions. 

For these software developers, Java plays a pertinent role daily. But be it any coding language, we all face specific problems that require a quick solution. Hence, Java Design Patterns come into play. These Design patterns offer a quick solution that can help solve varied technical issues. Feel like exploring it more and pursuing a career in the same? How about we take a quick look at some interesting facts on java design patterns and go through the tips related to this career choice. We have enlisted, in this article, a few java design patterns interview questions to crack a job interview?

About Java Design Patterns

Design patterns are the design-level solutions for software engineers who face recurring problems daily. In contrast, some might confuse design patterns with code. However, it is more like a description that shares how to tackle a problem and further help with designing the solution.

It is an effective method to evade repeating problems. This method is tried and tested, which usually leads to higher readability of the final code. The design patterns are curated and used by OOP languages like Java. Let's explore this topic further and identify the advantages behind using this Pattern.

Advantages of Using Design Patterns

  1. It can be reused for multiple projects.
  2. It brings transparency to the design of an application.
  3. Created with the help of expert software developers, this Pattern provides effective and testified solutions.
  4. It helps design a better structure and suggests excellent solutions to improve the system architecture.

What's the Right Time to Use Design Patterns?

Design Patterns are used in the research and analysis phase of the Software Development Life Cycle. It's essential to use it at this stage as it helps provide professional guidance, which further aids in easing down the research and analysis process.

How Do We Categorize Design Patterns?

Design Patterns are categorized into two parts-

  • Core Java Design Patterns
  • JEE Design Patterns

Core Java Design Patterns

Core Java Design Patterns are further categorized into three categories- 

  • Creational Design patterns 
  • Structural Design patterns 
  • Behavioral Design patterns

To deep dive into these patterns ahead, here are the patterns that are categorized under the respective Pattern-

  • Creational Design Pattern further includes Factory Pattern, Abstract Factory Pattern, Singleton Pattern, Prototype Pattern, and Builder Pattern.
  • Structural Design Pattern includes Adapter Pattern, Bridge Pattern, Composite Pattern, Decorator Pattern, Facade Pattern, Flyweight Pattern, and Proxy Pattern.
  • Behavioural Design is classified as Chain of Responsibility Pattern, Command Pattern, Interpreter Pattern, Iterator Pattern, Mediator Pattern, Memento Pattern, Observer Pattern, State Pattern, Strategy Pattern, Template Pattern, and Visitor Pattern.

J2EE Patterns

  • MVC Pattern
  • Data Access Object Pattern
  • Front Controller Pattern
  • Intercepting Filter Pattern 
  • Transfer Object Pattern

Learning Road Map and Tools-

Patterns are much more than just words or formulas. With regular practice, one can accomplish this thing perfectly.

Here's a simple and quick guide on how you can achieve Java Design Pattern-

  1. Try your hand at C++, Java, or Python.
  2. Get your hands on GoF Design Pattern Book.
  3. Keep experimenting with new codes as per the tutorials or guidebook.
  4. Keep working on Array, Stacks, Enums, etc.

Required Skills

To become a Java Developer, you should have these significant skills-

  • Basic knowledge of Coding
  • Must be aware of Java
  • Object-Oriented Programming
  • Understanding of System Design and Architecture
  • Java Build Tools
  • Code Version Control
  • Web Frameworks

Some of the recent trends are-

  1. DevOps- It is the union of Software development and Information Technology. They have complete knowledge of the lifecycle of the application.
  2. Big Data- This helps to align more complicated and heavy data.
  3. Serverless Architecture- In this trend, one doesn't require someone to control and manage the infrastructure of a physical server.
  4. Spring Framework- It is considered one of the most influential frameworks. It is lightweight and easy to deploy in Java technology.

Opportunities and Salaries

After learning this skill, one can become an influential software designer. It can help get the best IT job out there, and one can expect an average salary of Rs. 70,000 per month in the starting stage. Software Engineer who knows Design Pattern earn an average of ₹18.8lakhs, mostly ranging from ₹15.0 lakhs to ₹33.8lakhs

100 Java Design Pattern Interview Questions and Answers-

Here are 100 Java Design Pattern interview questions that can help you crack your interview and make a career in this field.

1. What are the different types of Proxies?

Some of the different proxies are-

  • Protection Proxy- It helps to control access to the real subject.
  • Virtual Proxy- It is used to instantiate the expensive object.
  • Caching Proxy- It is used to cache expensive calls to the real subject.
  • Remote Proxy- It is used in distributed object communication.
  • Smart Proxy- It is used to log calls to the underlying object's members.

2. Can we write Thread-Safe Singleton in Java?

Thread-Safe Singleton in Java can be written in many ways-

  • It can be written by writing Singleton using double-checked locking
  • Using Static Singleton Instance initialized during class loading
  • By using Java Enum; this is considered to be the most straightforward way

3. What is Gang of Four (GoF)?

A book titled Design Patterns Elements of Reusable Object-Oriented Software was published in 1994. The names of the authors were Erich Gamma, Ralph Johnson, Richard Helm, and John Vlissides. The book was based on establishing knowledge related to Design Patterns in Software Development. The four authors of this book are known as the Gang of Four (GoF).

4. What are Creational Patterns?

Creational Design Patterns resemble the way of creating Objects. This design pattern provides solutions to instantiate an Object in the best way possible to share solutions.

5. Define Singleton Pattern?

This Pattern restricts the instantiation of a class and ensures, among several instances, that only one example of the class exists in the Java Virtual Machine. While it's a one-time solution, the implementation process is complex.

6. What is Factory Pattern?

Factory Design Pattern is required when we have multiple subclasses in a superclass and need to return to one of the sub-class based on the input. This Pattern helps to take out the responsibility of instantiating a class from the client program to the factory class.

7. What is Abstract Factory Pattern?

Known as the factory of factories, Abstract Factory Pattern is required to eliminate the 'if-else' block and align the factory class for every sub-class. After this, we have an Abstract Factory Class that will aid in returning the sub-class based on the input factory class.

8. What is Builder Pattern?

This Pattern works in support of Factory and Abstract Factory design patterns. It is usually used when the Object contains a lot of attributes. It works by opting for many optional parameters and helps build the Object by proposing a step-by-step process. It also offers a method that will help return the final Object.

9. What is a Prototype Pattern?

Suppose you have an Object creation in mind. However, it turns out that it is costly and drains plenty of your time and resources. But if you have a similar existing Object, Prototype Pattern can help you copy the original Object to a new Object. One can also modify it according to the needs. Java cloning is used by Prototype Pattern to copy the Object.

10. What are Structural Design Patterns?

To create varied class structures, Structural Patterns are used. It helps in providing different ways to curate class structure by using inheritance and composition. 

11. What is Adapter Pattern?

The Adapter Design Pattern comes under the Structural design pattern category. It focuses on amalgamating two unrelated interfaces to work together efficiently.

12. What is a Composite Pattern?

If we need to create a structure where Objects in the structure are to be treated the same, a composite design pattern is preferred. Categorized under Structural Design Patterns, it represents a part-whole hierarchy.

13. What is Proxy Pattern?

As the meaning suggests, the proxy is an alternative or placeholder for another Object to control access to it. It comes under Structural Design Pattern and is used to control the access that has to be provided for functionality. 

14. What is a Flyweight Pattern?

This Design Pattern reduces the load on memory by sharing Objects. Every Object consumes sufficient memory space, which can be challenging for low-memory devices like mobile or embedded systems. Hence, we use the Flyweight Design Pattern to reduce and evade the load on memory. The best example to portray this is - String Pool Implementation.

15. Explain Facade Pattern?

A Facade Pattern makes the workflow more efficient and smooth for the client. Daily, we might use different interfaces to acquire different types of databases and generate reports. However, with an increase in workload comes complexity, leading to difficulty in work management. Hence, Facade Pattern comes to the rescue and provides a wrapper interface on top of the existing interface for better workflow.

16. What is the Bridge Pattern?

It comes under Structural Design Patterns. The Bridge Design Pattern is used to segregate the interfaces from implementation. It is done to hide the implementation details from the client programs. Bridge Design Pattern is mainly required when we have interface hierarchies in both interfaces and implementations.

17. What is a Decorator Pattern?

The Decorator Design Pattern helps modify the functionality of an Object while it's in runtime. It ensures that other instances resembling the same class are not affected, and the individual Object gets the modified behavior. This is structured under Structural Design Patterns.

18. What are Behavioural Design Patterns?

The main aim of Behavioural Patterns is to provide loose coupling and flexibility to extend the functionality easily. It aids in providing solutions for better interaction between Objects.

19. What is the Template Method?

The Template Method is structured under Behavioral Design Pattern. The primary purpose is to curate a method stub and suspend some of the implementation steps for the subclasses. It also offers a default implementation that might be common for some or all the subclasses.

20. What is the Mediator Design Pattern?

As the name suggests, Mediator Design Pattern acts as the mid-point between different Objects in the system. This application turns out to be very helpful when varied Objects interact with each other. It steps in the process, leading to higher costs and more complexity. Instead of making Objects interact directly, leading to tightly coupled system components- the mediator aids in implementing loose coupling between Objects.

21. What is the Chain of Responsibility Pattern?

Structured under Behavioural Design Patterns, the Chain of Responsibility Pattern aids in acquiring loose coupling in software design. In this process, a request from the client is passed to a chain of Objects to help in the efficient processing of the same. Later the Object in the chain decides who will be processing the request. Sometimes, it is also determined whether the request should be sent to the next Object or not.

22. What is the Observer Pattern?

Observer Design Pattern is categorized under Behavioral Design Pattern. This process is helpful for those who are interested in understanding the state of an Object and want to stay updated on further changes. In this process, the Object that keeps an eye on the state of another Object is called an observer, and the Object which is watched is called the Subject.

23. What is the Strategy Pattern?

Also known as Policy Pattern, a Strategy Pattern is used when multiple algorithms for a specific task and actual implementation are used at runtime as per the clients' decision.

24. What is the Command Pattern?

Command Pattern is recognized under Behavioral Design Patterns. It is used to implement loose coupling under the request-response model. In this process, the request is sent to the invoker, and the invoker further passes it to the command Object. In the next step, the command Object passes the request to the apt method of the receiver. The receiver additionally performs the specific action.

25. What is the State Pattern?

The State Pattern is used to offer a loosely coupled and effective way to perform different actions based on the state. It is usually used when the Object changes its behavior considering the internal state. To execute this process- if it is required to change the behavior of an Object, then with the help of State Variable and acquiring an if-else condition block, one can perform different actions.

26. What is a Visitor Pattern?

The Visitor Pattern works when the focus is on operating on a group of similar kinds of Objects. This Pattern helps move the operational logic from familiar Objects to another class.

27. What is Interpreter Pattern?

The Interpreter Pattern is used as a grammatical representation of a language. It shares an interpreter that helps deal with this grammar.

28. What is the Iterator Pattern?

It is one of the Behavioral Patterns used to aid with a standard way to traverse through a group of Objects. Used in Java Collection Framework, this Iterator Pattern provides varied methods for traversing through a collection. Not only that, but one can also provide different kinds of iterators as per the requirement. 

29. What is a Memento Pattern?

The Memento Design Pattern offers to save the state of an Object so that we can focus on keeping it later. This Pattern is implemented with two Objects- Originator and Caretaker. The Originator is the Object which needs to be saved and restored. It requires an inner class to save the state of an Object. This internal state is private, which other Objects can use further.

30. What is the DAO Design pattern?

DAO stands for Data Access Object, a design pattern used to decouple the data persistence logic to a completely separate layer. The main idea is to separate the service layer from the Data Access Layer. 

31. What is the Dependency Injection Pattern?

Dependency Injection Pattern helps transform our application from a complex one to a loosely coupled one. It allows for removing hard-coded dependencies. It ensures that the application is extendable and maintainable. Dependency Injection Pattern can be injected in Java to shift the dependency resolution from compile-time to runtime.

32. What is the MVC Pattern?

MVC is known as Model-View-Controller. It is known as the oldest architectural Pattern to curate web applications.

33. What are the critical characteristics of Singleton Design Pattern?

  • It is used for caching, logging, and thread pool.
  • It is used in varied design patterns like Abstract Factory, Facade, Builder, etc.
  • Singleton Design Pattern restricts the instantiation of a class and ensures that only one class exists in the Java Virtual Machine.

34. What are the standard concepts of Java Singleton Pattern Implementation?

  • The Private constructor restricts the instantiation of the class from other classes.
  • The only class instance is the Private Static Variable of the same class.

35. What is Eager Initialization?

Eager Initialization refers to the implementation process of Singleton Pattern. In this stage, the instance of Singleton Class is curated at the time of class loading. It is also the easiest way to curate a singleton class; it comes with a drawback: it is created even when the client's application might not be using it.

36. What is Static Block Initialization?

Like Eager initialization, Static Block Initialization stands out while curating the instance of the class developed in the static book. It also provides an option for exception handling.

37. What are the advantages of Factory Design Pattern?

  • The priority of Factory Design Pattern is to create an approach to code for interface instead of implementation.
  • This Pattern aids in removing the instantiation of actual implementation classes from client code. 
  • The focus of this Pattern is to make code more robust, easy to extend, and less coupled.
  • It helps to provide abstraction via inheritance between implementation and client classes.

38. What are the examples of Abstract Factory Design Pattern?

  • javax.xml.parsers.DocumentBuilderFactory#newInstance()
  • javax.xml.transform.TransformerFactory#newInstance()
  • javax.xml.xpath.XPathFactory#newInstance()

39. What are the advantages of Abstract Factory Design Pattern?

  • It focuses on providing code for interface instead of implementation.
  • As one can easily add more products, Abstract Factory Design Pattern is also known as "Factory of Factories".
  • It avoids the conditional logic of the Factory pattern.

40. What are the three significant issues with Factory and Abstract Factory design patterns when the Object holds a lot of attributes?

  • Several times the arguments received from the client are the same. 
  • Some of the parameters can be optional, but sending all the parameters as NULL in the Factory Pattern is compulsory.
  • Due to heavy Objects and complex creation, the Factory class has to go through all the complexity, which can be confusing.

41. How can you build a Builder Design Pattern in Java?

Step 1- Create a static nested class and copy-paste all the arguments to Builder Class from Outer Class.

Step2- Make sure that the name convention is correct. E.g., If the class name is 'Computer', the Builder class should be named 'ComputerBuilder'.

Step3- The Builder Class should include a public constructor with the required attributes as parameters.

Step4- It should include methods to set the optional parameters and carry back the same Builder Object once the optional attribute is set.

Step5- The last includes the build() method. This will help return the Object needed by the client program.

42. What are the examples of Builder Design Pattern in Java?

Here are two examples of Builder Design Pattern in Java-

  • java.lang.StringBuilder#append() (unsynchronized)
  • java.lang.StringBuffer#append() (synchronized)

43. What is an example of a Prototype Design Pattern?

Suppose we have an Object that loads from the database that needs to be modified several times in the program. Instead of creating the Object using a new keyword and loading the data again, it's recommended to copy the data and make specific changes. With Prototype Design Pattern, one can copy the Object features as it makes it compulsory. Hence, it makes the data accessible.

44. What is a Two Way Adapter Pattern?

 The adapter pattern consists of two approaches- Class Adapter and Object Adapter. 

  • Class Adapter uses Java Inheritance and helps extend the source interface.
  • Object Adapter consists of the source Object and uses Java Composition.

45. Highlight the Adapter Design Pattern Class Diagram.


46. Example of Adapter Design Pattern in JDK.

  • java.util.Arrays#asList()
  • (returns a Reader)
  • (returns a Writer)

47. What are the different Objects of Composite Design Pattern?

The different Objects of the Composite Design Pattern are Base Component, Leaf and Composite.

  • Base Composite is the interface used for all Objects in the composition. The client program prefers this component to work with the Objects in the composition.
  • Leaf helps define the behavior of the elements in the composition. Ths Object doesn't come with any reference to other components. It aids in a building block for the composition and implements base components.
  • Composite carries leaf elements and implements the operation in the base component.

48. Share some essential points to keep in mind while implementing Composite Design Pattern.

  1. This Pattern can be used to curate tree-like structures. 
  2. This should be applied only when the group of Objects behave as a single Object.

49. Give one example of a Composite Design Pattern?

One of the best examples of Composite Design Pattern is- java.awt.Container#add(Component) 

50. What are some factors to consider before applying Flyweight Design Pattern?

  • The Object curation can be a time-consuming and heavy load on memory.
  • The attributes can be divided into intrinsic and extrinsic properties.
  • The client program should clarify the extrinsic properties of the Object.
  • The number of Objects created by the application should be huge.

51. What is the difference between Intrinsic and Extrinsic properties?

Intrinsic properties make the Object unique, while Extrinsic properties are planned and set by the client code and used to perform different functions.

52. What are the essential points to keep in mind for Flyweight Design Pattern?

  • This design pattern can lead to complexity and considerable memory and time consumption. Hence, it is important to use it wisely.
  • This Pattern is not effective if the Object's intrinsic properties are enormous. It can lead to an increment in the complexity of the process.

53. What is an example of a Flyweight Dress Pattern in JDK?

The best example in this situation is the Java String class, String Pool Implementation.

54. According to GoF, what's the meaning of Facade Design Pattern?

As per GoF, Facade Design Pattern means- 'Provide a unified interface to a set of interfaces in a subsystem. Facade Pattern defines a higher-level interface that makes the subsystem easier to use.'

55. What are the important points to keep in mind for the Facade Design Pattern?

  • The usage of the Facade Design pattern is entirely dependent on the client's code as it acts more like a helper. It refrains from hiding subsystem interfaces from the client.
  • This Pattern can be used at any given point in time, even when the system gets complex.
  • The main aim of Facade Design Pattern is to provide a single interface rather than multiple interfaces with similar attributes and functionality.
  • One can use Factory Pattern with Facade to offer a better interface to client systems.

56. How is the Bridge Design pattern structured?


57. According to GoF, what's the definition of a Bridge Design Pattern?

As per GoF, Bride Design Pattern stands for 'Decouple an abstraction from its implementation so that the two can vary independently.’

58. Where can Bridge Design Pattern be used?

Bridge Design Pattern can be used when abstraction and implementation have different hierarchies that vary independently. It is mainly used to hide the implementation from the client application.

59. What does Composite Pattern Base Component define?

This Component highlights the standard methods for leaf and composites. It aids in creating a class Shape with the draw (String fillColor) process to draw the shape with the given or existing color.

60. What do Composite Design Pattern Leaf Objects define?

Composite Design Pattern Leaf Objects implements the base component. These are known as the building block for the composite. We can curate multiple leaf Objects such as Triangle, Circle etc.

61. What does a Composite Object consist of?

It consists of leaf Objects. It also provides helper methods that further help add or delete leaves from the group. It can also lead to removing all the elements from the group.

62. What are the important points to keep in mind for Composite Pattern?

  • This Pattern should be applied only when the group of Objects starts behaving as a single Object.
  • It is used to curate a tree-like structure.

63. State an example of a Composite Pattern in Java?

java.awt.Container#add(Component) is the best example in JavaJava. It is also used a lot in Swing.

64. Share an example of a Decorator Design Pattern?

The Decorator Design Pattern works in the system of Hierarchy. E.g., one can create an interface car to define the overall structure. It designs the basic car, which can further be segregated into Sports and Luxury Cars.

65. What is the class diagram of the Decorator Design Pattern?


66. What are the important points to keep in mind for the Decorator Design Pattern?

  • This Pattern is easy to maintain and can be extended when the number of choices is more in number.
  • This Pattern is flexible and helpful in providing runtime modification abilities.
  • The disadvantage that this Pattern carries along is that it uses a lot of similar kinds of Objects.

67. Where is the Decorator Pattern used?

It is used in Java IO classes like FileReader, BufferReader etc.

68. How can you create a Singleton Pattern?

There are two ways of creating a Singleton Pattern- Early Instantiation and Lazy Instantiation.

  • Early Instantiation is responsible for the creation of instances at the load time.
  • Lazy Instantiation is responsible for the curation of instances as and when required.

69. What are the two helper interfaces of Facade Design Pattern?

In Facade Design Pattern, we have two helper faces: MySqlHelper and OracleHelper.

70. What is Java Enum?

Java Enum was introduced in Java 1.5. It is launched in a field that consists of a fixed set of constraints. E.g., with Java Enum, we can create fixed fields like EAST, WEST, NORTH, and SOUTH.

71. What is the strategy to describe a Design Pattern?

Here are the following things to keep in mind while describing a Design Pattern-

  • Name and Classification of Pattern
  • The Problem and Solution
  • Identification of Uses and their efficiency

72. According to GoF, what does Flyweight Design Pattern mean?

As per GoF, Flyweight Design Pattern means 'Use sharing to support large numbers of fine-grained Objects efficiently.'

73. In which category does Flyweight Design Pattern come in?

Flyweight Design Pattern comes under Structural Design Pattern like Adapter Pattern, Facade Pattern etc.

74. What is the example of a Flyweight Design Pattern in JDK?

The most suitable example is the valueOf() method which uses cached Objects showing the usage of the Flyweight Design Pattern.

75. What are the important points to keep in mind for Flyweight Design Pattern?

  1. This design pattern works entirely on the design decision of whether the client code should use flyweight pattern implementation or not.
  2. It can lead to complexity, and if the number of shared Objects is higher, it can lead to further complications.
  3. This Pattern is not helpful if the number of intrinsic properties of the Object is huge.

76. What is the intent of the Proxy Design Pattern as per GoF?

As per GoF, the intent of the Proxy Design Pattern is- 'Provide a surrogate or placeholder for another Object to control access to it.'

77. What is the common usage of Proxy Design Pattern?

The standard uses consist of -

  • Control access
  • Provide a wrapper implementation for better performance

78. What are the examples of Chain of Responsibility Design Pattern in JDK?

Here are the following two examples-

  • java.util.logging.Logger#log()
  • javax.servlet.Filter#doFilter()

79. What are the important points to keep in mind for the Chain Of Responsibility Design Pattern?

  • Every Object in the connected chain should have a reference to the next Object. This will help carry forward the request achieved by Java Composition.
  • One should curate an error-free chain, or it can lead to rejection in the request, which will never be forwarded to a specific processor.
  • This Pattern is considered to achieve loose coupling.
  • It comes with a lot of complexities like maintenance problems etc.

80. What is Java Composition?

Java Composition can be achieved with the help of instance variables. These instance variables refer to different Objects.

81. What is a Command Design Pattern Class Diagram?


82. What are the important factors to keep in mind for Command Design Pattern?

  • Command leads the whole Pattern; this defines the contract for implementation.
  • Command implementation is segregated from receiver implementation.
  • Invoker Class's responsibility is to forward the request from the client to the command Object.
  • This design pattern is readily extendible.

83. What is the Command Design Pattern JDK Example?

java.lang.Runnable and javax.Swing.Action uses Command Pattern.

84. Showcase Interpreter Design Pattern Class Diagram.


85. What are the important things to keep in mind for Interpreter Design Pattern?

  • This Pattern can be used to create a syntax tree for the grammar.
  • The Interpreter pattern requires excessive proofreading and error checking.

86. What are some of the patterns used in the JDK of Interpreter Design Pattern?

java.util.Pattern and java. text.Format are some of the examples of the patterns used in the JDK of Interpreter Design Pattern.

87. According to GoF, what does Iterator Design Pattern mean?

As per GoF, this Pattern means- 'Provides a way to access the elements of an aggregate Object without exposing its underlying representation.'

88. What are the important points to keep in mind for Iterator Design Pattern?

  • This Pattern helps hide the implementation logic from the client program.
  • It helps to provide a standard way to iterate over a collection.
  • The logic for iteration is embedded in the collection itself, making it easier for the client to iterate.

89. What is the implementation of the Iterator Design Pattern in JDK?

Collection framework Iterator is considered the best example. However, JavaJava.util.scanner also implements the Iterator Design Pattern.

90. What is the intent of the Mediator Design Pattern as per GoF?

The intent is - 'Allows loose coupling by encapsulating how disparate sets of Objects interact and communicate with each other. Allows for the actions of each Object set to vary independently of one another.'

91. What is the Mediator Design Pattern class diagram?


92. What is the Mediator Design Pattern example in JDK?

  • java.util.Timer class scheduleXXX() methods
  • Java Concurrency Executor execute() method.
  • java.lang.reflect.Method invoke() method.

93. What are the important points to keep in mind for the Mediator Design Pattern?

  • This Pattern is used when there are little complications in the communication logic between two Objects.
  • The mediator pattern is used by Java Message Service to publish data to other applications.
  • One should refrain from using Mediator Design Pattern to achieve loose coupling as the process can get a little complicated in the future.

94. What are the two Objects used to implement the Memento Design Pattern?

Two Objects that are used are- The originator and the Caretaker.

95. What are the important points to keep in mind for the Memento Design Pattern?

  • This Pattern should be accessible only to the Originator Object.
  • For saving and restoring the Originator stake, the Caretaker Object should be used.

96. As per GoF, what does the Observer Design Pattern mean?

As per GoF, Observer Design Pattern implements- 

'Define a one-to-many dependency between Objects so that when one Object changes state, all its dependents are notified and updated automatically.'

97. State Observer Design Pattern Class diagram.


98. What are some of the implementations of the Observer Design Pattern?

Some of the implementations are-

  • java.util.EventListener in Swing
  • javax.servlet.http.HttpSessionBindingListener
  • javax.servlet.http.HttpSessionAttributeListener

99. What are the benefits of the State Design pattern?

Some of the benefits are-

  • Fewer chances of facing errors.
  • Easier to add more states for additional behavior.
  • It is easily maintainable and flexible.

100. What is the second word for Strategy Design Pattern?

Strategy Design Pattern is also known as Policy Pattern.

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