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.


Create the following java program using any editor of your choice.


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>();
      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) {

   public E getItem(int index) {
      return list.get(index);

This will produce the following result.


Integer Value :10
String Value :Hello World
(Pair)Integer Value :10
(CustomList)Integer Value :10