• Proficiency in Java, with a good understanding of its ecosystems
• Sound knowledge of Object-Oriented Programming (OOP) Patterns and Concepts
• Familiarity with different design and architectural patterns
• Skill for writing reusable Java libraries 
• Knowhow of Java concurrency patterns
• Basic Understanding of the concepts of MVC (Model-View-Controller) Pattern, JDBC (Java Database Connectivity), and RESTful web services
• Experience in working with popular web application frameworks like Play and Spark
• Relevant Knowledge of Java GUI frameworks like Swing, SWT, AWT according to project requirements
• Ability to write clean, readable Java code
• Basic knowhow of class loading mechanism in Java
• Experience in handling external and embedded databases
• Understanding basic design principles behind a scalable application
• Skilled at creating database schemas that characterize and support business processes
• Basic knowledge of JVM (Java Virtual Machine), its drawbacks, weaknesses, and workarounds
• Implementing automated testing platforms and unit tests 
• In-depth knowledge of code versioning tools, for instance, Git
• Understanding of building tools like Ant, Maven, Gradle, etc
• Expertise in continuous integration

Other required skills of java developer include the basic knowledge of:

• JavaServer pages (JSP) and servlets
• Web frameworks like Struts and Spring
• Service-oriented architecture 
• Web Technologies like HTML, JavaScript, CSS, JQuery
• Markup Languages such as XML, JSON
• Abstract classes and interfaces
• Constructors, lists, maps, sets
• File IO and serialization
• Exceptions
• Generics
• Java Keywords like static, volatile, synchronized, transient, etc
• Multithreading and Synchronization