What is .NET equivalent in Java?
                                
                                    NET platforms. Java has its own virtual machine, the Java Virtual Machine (JVM) which is similar to . NET CLR. Java's execution engine (the JVM) and a Java compiler with a set of libraries constitute the Java Platform.
                                 
                                                            What is .NET similar to?
                                
                                    ASP.NET, Java, Python, PHP, and JavaScript are the most popular alternatives and competitors to . NET.
                                 
                                                            Can we use Java with .NET framework?
                                
                                    While we can write and execute applications entirely in Java and the . NET Framework independently. Programmers use the JNI to write native methods to handle those situations when an application cannot be written in Java and . NET independently.
                                 
                                                     
                        
                    
.NET --> Java
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WCF ~= JAX-WS (as WS) and/or JMS (for MQ).
 
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WPF ~= Swing (as UI), Java 2D (for 2D), Java 3D (for 3D) and/or RMI (for remoting).
 
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Silverlight ~= JavaFX
 
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WF ~= not sure? Some say that it's CAPS.
 
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Generics is already available since Java 5.0. Major difference is that it's compiletime (not Reified).
 
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Lambda expressions is yet to be come in Java 8.0 as "Closures"
 
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Linq ~= Jaque and jpropel-light
 
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TPL ~= 
java.util.concurrent (guide here and tutorial here) 
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F# ~= Scala or Clojure
 
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IronPython ~= Jython
 
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IronRuby ~= JRuby
 
Java --> .NET
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EJB ~= MTS/COM+
 
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WebSphere AS, GlassFish, JBoss AS are all concrete Java EE API implementations. The .NET equivalent would be IIS with at least MTS/COM+ support (is there by the way competition for IIS?).
 
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Tomcat is a webcontainer aka servletcontainer, it only implements the Web Component part of the huge Java EE API (basically only the 
javax.el and javax.servlet parts, the JSP/EL and Servlet API). The .NET equivalent would be still IIS, but then without support for MTS/COM+, mail, message queue, persistence and more. I.e. only a simple web server for pure "Classic ASP". 
Here is a list from my own research and follow up on BalusC's, Rafa's (et al.) answers:
(Slowly updating this list. Will also provide links back to .NET technologies for Java folks who may be interested.)
- WCF
 
- WPF
 
- 
Silverlight = JavaFx
 
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WF = jBMP (Java Business Process Management)
 
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Generics = Java Generics
 
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Lambda expressions = lambdaJ project or Closures
 
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Linq (not Linq-to-SQL) = jaque or Quaere
 
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TPL ~= java.concurrent package
 
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F# = Scala
 
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IronPython = JPython
 
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IronRuby = JRuby
 
- Hibernate = NHibernate
 
- JUnit = NUnit
 
- Spring = Spring.NET
 
- .Net Remoting ~= RMI
 
- MEF/System.AddIn ~= OSGi/Jigsaw
 
- ~= EJB
 
- ~= WebSphere
 
- ~= GlassFish
 
- ~= JBoss App Server
 
- ~= Tomcat?
 
- ~= GWT
 
- ~= Maven2/Nexus/Sonatype
 
- ~= JMX
 
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ClickOnce ~= Java Web Start
 
JavaFX is the rough equivalent of Silverlight.  That's all I know from that list...
    
The main technologies are already covered, so a few peripheral technologies:
- TPL ~= java.concurrent package
 
- F# ~= Scala
 
- IronPython/IronRuby ~= Jython/JRuby
 
- .Net Remoting ~= RMI
 
- MEF/System.AddIn ~= OSGi/Jigsaw
 
To the growing list I submit:
- 
ClickOnce ≅ Java Web Start