Java generics examples -- parameterized class

Not only can Java generics be used in fields and methods, it can also be used in class definitions to produce parameterized classes. Since JDK 1.5, many built-in Java classes have been retrofitted to parameterized forms. An example is java.lang.Class, which is declared to be public final class Class<T>, the parameter type <T> represents the actual type modeled by this Class object. One benefit is that some of its methods can take or return specific types, avoiding casting while enforcing type-check.

It's also easy to write your own parameterized class. The following is a Member class whose Id field can be parameterized to String, Integer, etc:

package javahowto;
public class Member<T> {
 private T id;
 public Member(T id) {
   this.id = id;
 }
 public T getId() {
   return id;
 }
 public void setId(T id) {
   this.id = id;
 }
 public static void main(String[] args) {
   Member<String> mString = new Member<String>("id1");
   mString.setId("id2");
   System.out.printf("id after setting id: %s%n", mString.getId());
   //output:  id after setting id: id2

   Member<Integer> mInteger = new Member<Integer>(1);
   mInteger.setId(2);
   System.out.printf("id after setting id: %d%n", mInteger.getId());
   //output:  id after setting id: 2
 }