What is the difference between these two talend components, as both are used to make use of Java code during transformation phase.
The tJavaRow must be inside a flow and will affect each row of a flow going throught.
The tJava can't be part of a flow : it must be connected to other components with triggers : "OnComponentOK" / "OnSubjobOK" / "If" or with an "Iterate". You can use it to initialize context variables for instance.
The tJavaFlex is a mix of both : it can be part of a flow but also disconnected from it. Its use is a bit more complex, so I would advise not using it until you are more familiar with tJava and tJavaRow.