Is it really that important to know the core feature of a language?
Is it really that important to know/master the core features of language before moving to its sub catagories? Or is it okay if you're familiar with its core?

Let's say I am java developer where I am familiar with the Fundamentals of OOP and the core  java. like (Nested Types,Generics,Abstract,Interfaces,Inheritance,Polymorphism , I/O,Swing) with these skill set is it okay to change my learning road map to Java Web development(I'll start with Java Server Pages and JSF). or should I learn more about the other core features of java like Concurrency and Object Serialazation (I haven't grasp their concept 100%).
Is it really that important to know the core feature of a language?
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Is it really that important to know/master the core features of language before moving to its sub catagories? Or is it okay if you're familiar with its core?

Let's say I am java developer where I am familiar with the Fundamentals of OOP and the core  java. like (Nested Types,Generics,Abstract,Interfaces,Inheritance,Polymorphism , I/O,Swing) with these skill set is it okay to change my learning road map to Java Web development(I'll start with Java Server Pages and JSF). or should I learn more about the other core features of java like Concurrency and Object Serialazation (I haven't grasp their concept 100%).