Why do we need no-arg constructor?

The arguments of a constructor can only be found by type, not by name, so there is no way for the framework to reliably match properties to constructor args . Therefore, they require a no-arg constructor to create the object, then can use the setter methods to initialise the data.

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What is parameterized in Java?

A parameterized type is an instantiation of a generic type with actual type arguments . A generic type is a reference type that has one or more type parameters. These type parameters are later replaced by type arguments when the generic type is instantiated (or declared ).

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