”;
A type parameter cannot be used to instantiate its object inside a method.
public static <T> void add(Box<T> box) { //compiler error //Cannot instantiate the type T //T item = new T(); //box.add(item); }
To achieve such functionality, use reflection.
public static <T> void add(Box<T> box, Class<T> clazz) throws InstantiationException, IllegalAccessException{ T item = clazz.newInstance(); // OK box.add(item); System.out.println("Item added."); }
Example
package com.tutorialspoint; public class GenericsTester { public static void main(String[] args) throws InstantiationException, IllegalAccessException { Box<String> stringBox = new Box<String>(); add(stringBox, String.class); } public static <T> void add(Box<T> box) { //compiler error //Cannot instantiate the type T //T item = new T(); //box.add(item); } public static <T> void add(Box<T> box, Class<T> clazz) throws InstantiationException, IllegalAccessException{ T item = clazz.newInstance(); // OK box.add(item); System.out.println("Item added."); } } class Box<T> { private T t; public void add(T t) { this.t = t; } public T get() { return t; } }
This will produce the following result −
Item added.
Advertisements
”;