Java Generics - Classes

A generic class declaration looks like a non-generic class declaration, except that the class name is followed by a type parameter section.

The type parameter section of a generic class can have one or more type parameters separated by commas. These classes are known as parameterized classes or parameterized types because they accept one or more parameters.

Syntax

public class Box<T> {
   private T t;
}

Where

• Box − Box is a generic class.

• T − The generic type parameter passed to generic class. It can take any Object.

• t − Instance of generic type T.

Description

The T is a type parameter passed to the generic class Box and should be passed when a Box object is created.

Example

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

GenericsTester.java

package com.howcodex;

public class GenericsTester {
   public static void main(String[] args) {
      Box<Integer> integerBox = new Box<Integer>();
      Box<String> stringBox = new Box<String>();

      integerBox.add(new Integer(10));
      stringBox.add(new String("Hello World"));

      System.out.printf("Integer Value :%d\n", integerBox.get());
      System.out.printf("String Value :%s\n", stringBox.get());
   }
}

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.

Output

Integer Value :10
String Value :Hello World