Java Refresher Notes

📘 Step-by-step Java learning notes covering everything from fundamentals to J2EE and web apps. Includes concepts, examples, and explanations in easy-to-read Markdown format.

📂 Contents

1. Intro
2. Differences Between JDK, JRE and JVM
3. Data Types
4. Operators
5. OOPs (Object Oriented Programming)
6. Variables
7. Loops
8. Arrays
9. Functions (methods)
10. this keyword
11. Types of functions
12. Method Overloading (Compile time polymorphism)
13. var args
14. Passing object as argument
15. Passing Array of Objects to a method
16. Returning Value by a Method
17. Print an array element by element
18. Passing Objects as Arguments
19. String
20. Wrapper Class
21. Boxing, Unboxing, Autoboxing
22. String Class
23. Character Class
24. Date Class
25. String Handling
26. Typecasting
27. Java Scanner Class
28. Email Validation
29. Switch-Case Statement
30. StringBuffer Class
31. StringBuilder Class
32. Mutable string
33. Substring
34. Constructor
35. Types of Constructors
36. Access Modifiers
37. Getter and Setter Methods
38. Constructor Overloading
39. ASCII (American Standard Code for Information Interchange)
40. Inheritance
41. Polymorphism (Method Overriding – Runtime Polymorphism)
42. super keyword
43. Abstraction
44. Anonymous Class
45. Encapsulation
46. Interface
47. Abstract Class vs. Interface
48. Exception Handling
49. Inner Classes (Nested Classes)
50. File Handling
51. File class
52. Multithreading
53. Runnable Interface
54. isAlive() Method
55. Life Cycle of a Thread (Thread States controlled by JVM)
56. Synchronization
57. Inter-Thread Communication (ITC)
58. API (Application Programming Interface)
59. JDBC (Java Database Connectivity)
60. DriverManager Class
61. Connection interface
62. Statement interface
63. ResultSet interface
64. PreparedStatement Interface
65. Collections
66. List Interface
67. ArrayList Class
68. LinkedList Class
69. Difference between ArrayList and LinkedList
70. Garbage Collection
71. Finalize method
72. Serialization
73. J2EE Web application
74. Web Architecture and Network Basics
75. Servlet Fundamentals and Lifecycle
76. MVC (Model View Controller)
77. Servlet Interface and Its Functions
78. Content Types in HTTP and MIME
79. Servlet API
80. Steps to create a Servlet
81. Filters and Listeners in Servlet API
82. HttpServlet class
83. GET vs POST
84. GenericServlet Class
85. ServletRequest interface
86. CRUD in Servlet
87. Servlet Collaborations : RequestDispatcher and sendRedirect
88. ServletConfig Interface
89. ServletContext Interface
90. Attributes in Servlet
91. State Management
92. Session Tracking in Servlets
93. Servlet with Annotation
94. HTTP Session
95. Cookie Class
96. Hidden Form Field
97. Lambda Expression
98. HashMap
99. CAPTCHA
100. MD5 (Message Digest Algorithm 5)
101. JavaServer Pages (JSP)
102. JSP Implicit Objects
103. Types of JSP tags
104. EL (Expression Language)
105. JSP Lifecycle
106. JSP Elements
107. JSP Directives (page, include, taglib)
108. Include Directive vs <jsp:include> Action
109. JSP Action Tags
110. JavaBeans Architecture and <jsp:useBean>
111. JSP Error Handling
112. Custom Error Pages in JSP
113. JSTL (JavaServer Pages Standard Tag Library)
114. Core JSTL Tags (c:if, c:forEach, c:choose)
115. JSTL Functions (fn:length, fn:contains, etc.)
116. EL + JSTL vs JSP Scriptlets (Best Practices)
117. MVC Architecture using Servlet + JSP
118. JSP vs Servlet (Role in MVC Architecture)
119. Form Handling in JSP and Servlets
120. Form Validation (Client-side and Server-side)
121. Session Management in Web Applications
122. Login and Logout Flow using HTTP Sessions
123. Authentication and Authorization Basics
124. File Upload and Download in Web Applications
125. Pagination in Web Applications
126. J2EE / Jakarta EE Architecture Overview
127. WAR File Structure
128. Deployment Descriptor (web.xml)
129. Web Application Lifecycle
130. Servlet Authentication with JDBC (Login/Signup)
131. Role-Based Access Control (RBAC)
132. Servlet Filters for Authentication and Authorization
133. Session Security Best Practices
134. Cookies vs Sessions (Security Perspective)
135. CSRF and XSS Attacks
136. MVC Frameworks Introduction (Spring MVC, Jakarta MVC)
137. Database Connection Pooling (DataSource vs DriverManager)
138. DAO (Data Access Object) Pattern
139. MVC with DAO + JDBC + JSP
140. Front-End with Bootstrap in JSP Pages
141. AJAX with JSP/Servlet Backend
142. REST APIs with Java Servlets
143. JSON Handling in Servlets (Jackson / GSON)
144. WebSockets in Java
145. Deployment on Apache Tomcat (Step-by-Step)
146. Deployment on Cloud (Heroku / AWS / GCP)
147. Logging with Log4j or SLF4J + Logback
148. Unit Testing for Servlets and JSP (JUnit + MockMVC)
149. Integration Testing with Selenium + Java
150. Build Tools (Maven / Gradle) for Web Projects
151. CI/CD in Java Projects (GitHub Actions / Jenkins)