Generic Classes and Parameterized Types

Java Tutorials - Herong's Tutorial Examples

∟Generic Classes and Parameterized Types

This chapter provides tutorial notes and example codes on generic classes and parameterized types. Topics include what is a generic class; what is a type parameter; using parameterized types and subtyping; using wildcard parameterized types and subtyping.

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What Is a Generic Class

Using a Generic Class

Using a Generic Class - Example

Creating a Generic Class

Creating a Generic Class - Example

Bounded Type Parameters

Raw Type, Generic Type and Parameterized Type

Parameterized Type and Subtyping

Wildcard Parameterized Types

Wildcard Parameterized Type Test

Wildcard Parameterized Subtyping

Conclusion:

A generic class is a class that supports type parameters with different behaviors when given different types on invocation.
A generic class has a signature of ClassName<A, B, C, ...>.
Type parameters can be bounded as ClassName<T extends C & I1 & I2...> to ensure strong typing to reduce runtime type mismatches.
A parameterized type is a reference type for generic class objects with argument types provided.
Subtyping of parameterized types is based on their generic class hierarchy, like class Hashtable<K,V> extends Dictionary<K,V>.
Raw types for generic types introduced in JDK 1.5 are supported for backward compatibility.
A wildcard parameterized type is a parameterized type with argument types containing wildcards for subtyping purposes.
There 3 categories of wildcard parameterized types: unbounded, upper bounded and lower bounded.