Generic Types

Java Generic methods and generic classes enable programmers to specify, with a single method declaration, a set of related methods, or with a single class declaration, a set of related types, respectively.Generic in java is similar to templates in C++. It allows the user to parameterized the types in classes, or interface. The user have to <> to specify parameter types in generic class creation.

Generic Methods

public <T> methodName()
{
    ...
}

Generic class

public class ClassName<T>
{
    ...
}

Generic variable

T variableName;

Lets see a code sample to easily understand the generic types.

//This a Generic class declaration
class Generic<T> // This class accepts any data type
{
    // Generic variable declaration
    T variable;
    public Generic(T variable) // constructor  for generic class
    {
        this.variable = variable;
    }

    //generic method declaration
    public <T> getVariable() // method to get the variable of generic type
    {
        return variable;
    }
}

This the main class where the object for generic class is created here.

class Main
{
    public static void main(String args[])
    {
    // Here the object is created for Generic class of type Integer.
    Generic<Integer> intvar = new Generic<Integer>(20);
    System.out.println(intvar.getVariable());

    // Here the object is created for Generic class of type String.
    Generic<String> strvar = new Generic<String>("I love Java");
    System.out.println(strvar.getVariable());
    }

}

OUTPUT

20

I love Java

The code shows you that the class constructor while object creation can accept any data type.

Exercise

Create a Generic class which accepts String and Integer datatype at a time. Create a object for the same. Pass in 30 and "I love Generic types" as parameters. Print both in the next line.