What are the technologies a Java developer must know?

Every Java Developer should know the following core java concepts -

• OOPs Concepts
• Abstract Classes and Interfaces
• Constructors
• File IO and Serialization
• Collections - List , Map , Set
• Access Specifiers
• Exceptions - Checked , Unchecked
• Generics
• Java Keywords - Static , Final , volatile, synchronized , transient, this super etc.
• JVM and Memory Management
• Multithreading and Synchronization
• Design Pattern

If he wants to be a network / distributed application developer , he should know the following technologies

• Sockets
• RMI
• Interface APIs - JMS, JDBC
• ORMs - EJB ( Session Beans , Entity beans, MDB's ),  Hibernate

If he wants to be a web developer , he should know

• JSP
• Servlets / filters / Interceptors
• JNDI
• Architectures - n Tier, MVC
• Web Frameworks like Struts / Spring
• Service Oriented Architecture / Web Services ( optional for SOA developers )
• Web Technologies like HTML, CSS, Javascript and JQuery
• Markup Languages like XML and JSON.

If he wants to be a UI developer, he should know

• Applets
• Frameworks like Swing, SWT, AWT

Every Java Developer is expected to have Database Knowledge so he should know -

• Database Drivers
• Normalization / Denormalization
• SQL Queries - Inner Outer Joins, Group By , Having
• Stored Procedures
• Triggers
• Cursors