Generics In Java

A generic class in Java is a class that can work with different data types while providing type safety at compile time. It allows you to define a class with type parameters (placeholders for types), which are specified when you create an object of that class/

Why use Generics?

• Type Safety: Prevents runtime ClassCastException by catching type mismatches at compile time.

• Code Reusability: Write a single class/method that works with any type.

• Readability: No need for unnecessary type casting.

Syntax of a Generic Class

​class Box<T> {   // T is a type parameter
private T value;

    public void set(T value) {
this.value = value;
}

public T get() {
return value;
}
}

​Here:

• T is a type parameter (can be replaced by any type like String, Integer, Double, etc.).

• When you create an object, you specify the type.

Example Uses:

​public class Main {
public static void main(String[] args) {
// Box for String
Box<String> stringBox = new Box<>();
stringBox.set("Hello Generics");
System.out.println(stringBox.get());

// Box for Integer
Box<Integer> intBox = new Box<>();
intBox.set(100);
System.out.println(intBox.get());
}
}

Output

​Hello Generics
100

Commonly used type parameter names:

​

T – Type

E – Element(used in collections)

K – Key

V – Value

N – Number

​

Utilities of Generic Type In Collection Framework:

Without Generic

List names =   new ArrayList()  ; /* Names without Generics
names can contain any type of data 
that cause runtime Exception during geting same type of data */

names.add(  "Deepak")  ;
names.add(  123)  ;
names.add(  123.50)  ;
names.add(  true)  ;

/* By default type of below instaces are Object 
but to get specific type developer needs to type caste as per the data */

String n1 = (String) names.get(0); 
Integer n2 = (Integer) names.get(1);
​Integer n3 = (Integer) names.get(2); // Cause Runtime ClassCaste Exception

System.  out.println(n1)  ; // Deepak
System.  out.println(n2)  ; //123

With Generic

​​ 
List<String> names = new ArrayList<>();
names.add("Deepak");
names.add(123); // Compile time Error
names.add(123.50); // Compile time Error
names.add(true); // Compile time Error

String n1 =  names.get(0); // No Cast Needed
System.out.println(n1);

​​