GENERICS A generic type is a generic class or interface that is - - PowerPoint PPT Presentation

GENERICS

A generic type is a generic class or interface that is parameterized

• ver types.

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We’ve already seen examples of generic classes

ArrayList<T>; HashMap<K, V>;

Where T is being used to represent the type of each item in the ArrayList, and K and V are being used to represent the type of each key and value element in the HashMap.

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We can dene our own generic class too. A generic class is dened with the following format: The type parameter section, delimited by angle brackets (<>), follows the class name. It species the type parameters (also called type variables) T1, T2, ..., and Tn.

class name<T1, T2, ..., Tn> { /* ... */ }

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To make a class generic, we add <variable> into the class denition, like so:

public class Stack<T> { T[] contents; // the contents of this Stack int size; // number of items in this Stack public Stack() { // Note: We can't construct a generic T array by saying "new T[MAX_SIZE]". // But we can cast to a T[]. contents = (T[]) new Object[MAX_SIZE]; size = 0; } public void push(T value) { contents[size++] = value; } public T pop() { return contents[--size]; } }

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USING A GENERIC CLASS

When you actually create a Stack object with a specic datatype, this replaces T with this concrete type. Instead of passing an argument to a method, this line involves are passing a type argument — Integer in this case — to the Stack class itself. See more examples here:

Stack<Integer> integerStack;

https://docs.oracle.com/javase/tutorial/java/generics/types.html

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NAMING CONVENTIONS

The Java Language Specication recommends these conventions for the names of type variables:

Very short, preferably a single character, but evocative All uppercase to distinguish them from class and interface names

The most commonly used type parameter names are:

K - Key N - Number T - Type V - Value S,U,V etc - 2nd, 3rd, 4th types

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