Contents
- 1 What are the restrictions in using generic type that is declared in a class declaration?
- 2 How do I find the instance of a generic type?
- 3 How do you restrict a generic class?
- 4 What does it mean to have generic class in Java?
- 5 How are type parameters used in generic classes?
- 6 When do generic classes inherit from open constructed types?
What are the restrictions in using generic type that is declared in a class declaration?
Restrictions on Generics
- Cannot Instantiate Generic Types with Primitive Types.
- Cannot Create Instances of Type Parameters.
- Cannot Declare Static Fields Whose Types are Type Parameters.
- Cannot Use Casts or instanceof With Parameterized Types.
- Cannot Create Arrays of Parameterized Types.
How do I find the instance of a generic type?
To construct an instance of a generic type
- Get a Type object that represents the generic type.
- Construct an array of type arguments to substitute for the type parameters.
- Call the MakeGenericType method to bind the type arguments to the type parameters and construct the type.
How do you restrict a generic class?
Whenever you want to restrict the type parameter to subtypes of a particular class you can use the bounded type parameter. If you just specify a type (class) as bounded parameter, only sub types of that particular class are accepted by the current generic class.
Can you give an example of how generics make a program more flexible?
Can you give an example of how Generics make a program more flexible? MyList can be used to store a list of Strings only. This is problem that Generics solve. Instead of hard-coding String class as the only type the class can work with, we make the class type a parameter to the class.
How do you restrict a generic type parameter to use only a specific class?
What does it mean to have generic class in Java?
A Generic class simply means that the items or functions in that class can be generalized with the parameter(example T) to specify that we can add any type as a parameter in place of T like Integer, Character, String, Double or any other user-defined type.
How are type parameters used in generic classes?
Generic types can use multiple type parameters and constraints, as follows: Open constructed and closed constructed types can be used as method parameters: If a generic class implements an interface, all instances of that class can be cast to that interface. Generic classes are invariant.
When do generic classes inherit from open constructed types?
Generic classes that inherit from open constructed types must supply type arguments for any base class type parameters that are not shared by the inheriting class, as demonstrated in the following code:
Is there a static method in a generic class?
The answer I used was to put the generic in the method, not in the class definition. public class QuickSortArray { public static void quickSort (T [] array, int bottom, int top) { //do it } } Of course, after reading the answers above I realized that this would be an acceptable alternative without using a generic class: