What Are Generics? A Simple Generics Example : Generics Basics « Generics « Java Tutorial

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2. Generics
3. Generics Basics

The term generics means parameterized types. (Java 2 V5.0 (Tiger) New Features by Herbert Schildt )

1. T is a type parameter that will be replaced by a real type.
2. T is the name of a type parameter.
3. This name is used as a placeholder for the actual type that will be passed to Gen when an object is created.

class GenericClass<T> {
  T ob;

  GenericClass(T o) {
    ob = o;
  }

  T getob() {
    return ob;
  }

  void showType() {
    System.out.println("Type of T is " + ob.getClass().getName());
  }
}

public class MainClass {
  public static void main(String args[]) {
    // Create a Gen reference for Integers.
    GenericClass<Integer> iOb = new GenericClass<Integer>(88);
    iOb.showType();

    // no cast is needed.
    int v = iOb.getob();
    System.out.println("value: " + v);

    // Create a Gen object for Strings.
    GenericClass<String> strOb = new GenericClass<String>("Generics Test");
    strOb.showType();

    String str = strOb.getob();
    System.out.println("value: " + str);
  }
}

Type of T is java.lang.Integer
value: 88
Type of T is java.lang.String
value: Generics Test