- Java Generics Tutorial
- Java Generics - Home
- Java Generics - Overview
- Java Generics - Environment Setup
- Examples - Generic Classes
- Java Generics - Generic Classes
- Type Parameter Naming Conventions
- Java Generics - Type inference
- Java Generics - Generic Methods
- Java Generics - Multiple Type
- Java Generics - Parameterized Types
- Java Generics - Raw Types
- Examples - Bounded Type
- Bounded Type Parameters
- Java Generics - Multiple Bounds
- Examples - Collections
- Java Generics - Generic List
- Java Generics - Generic Set
- Java Generics - Generic Map
- Examples - Wild Cards
- Upper Bounded Wildcards
- Generics - Unbounded Wildcards
- Lower Bounded Wildcards
- Generics - Guidelines for Wildcards
- Type Erasure
- Java Generics - Types Erasure
- Java Generics - Bound Types Erasure
- Unbounded Types Erasure
- Java Generics - Methods Erasure
- Restrictions on Generics
- Java Generics - No Primitive Types
- Java Generics - No Instance
- Java Generics - No Static field
- Java Generics - No Cast
- Java Generics - No instanceOf
- Java Generics - No Array
- Java Generics - No Exception
- Java Generics - No Overload
- Java Generics Useful Resources
- Java Generics - Quick Guide
- Java Generics - Useful Resources
- Java Generics - Discussion
Type Parameter Naming Conventions
By convention, type parameter names are named as single, uppercase letters so that a type parameter can be distinguished easily with an ordinary class or interface name. Following is the list of commonly used type parameter names −
E − Element, and is mainly used by Java Collections framework.
K − Key, and is mainly used to represent parameter type of key of a map.
V − Value, and is mainly used to represent parameter type of value of a map.
N − Number, and is mainly used to represent numbers.
T − Type, and is mainly used to represent first generic type parameter.
S − Type, and is mainly used to represent second generic type parameter.
U − Type, and is mainly used to represent third generic type parameter.
V − Type, and is mainly used to represent fourth generic type parameter.
Following example will showcase above mentioned concept.
Example
Create the following java program using any editor of your choice.
GenericsTester.java
package com.tutorialspoint; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class GenericsTester { public static void main(String[] args) { Box<Integer, String> box = new Box<Integer, String>(); box.add(Integer.valueOf(10),"Hello World"); System.out.printf("Integer Value :%d\n", box.getFirst()); System.out.printf("String Value :%s\n", box.getSecond()); Pair<String, Integer> pair = new Pair<String, Integer>(); pair.addKeyValue("1", Integer.valueOf(10)); System.out.printf("(Pair)Integer Value :%d\n", pair.getValue("1")); CustomList<Box> list = new CustomList<Box>(); list.addItem(box); System.out.printf("(CustomList)Integer Value :%d\n", list.getItem(0).getFirst()); } } class Box<T, S> { private T t; private S s; public void add(T t, S s) { this.t = t; this.s = s; } public T getFirst() { return t; } public S getSecond() { return s; } } class Pair<K,V>{ private Map<K,V> map = new HashMap<K,V>(); public void addKeyValue(K key, V value) { map.put(key, value); } public V getValue(K key) { return map.get(key); } } class CustomList<E>{ private List<E> list = new ArrayList<E>(); public void addItem(E value) { list.add(value); } public E getItem(int index) { return list.get(index); } }
This will produce the following result.
Output
Integer Value :10 String Value :Hello World (Pair)Integer Value :10 (CustomList)Integer Value :10
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