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What is Generics in Java? | How IT Works | Scope & Skills

What is Generics in Java?

Generics in Java was introduced back in 2004 as a new function of the Java programming language and was a part of the JDK 5 release. It is most generally used along with the Java collections framework. As of in the present day it is one of the crucial outstanding and sought after function of the Java programming language.

Generic Java was discovered by four people specifically Gilad Bracha, Martin Odersky, David Stoutamire and Philip Wadler in 1998. It was an extension of the Java language that supported generic varieties. It was meant to realize two primary objectives which are:

  1. Sort safety
  2. Code reusability

Definition Of Generics in Java

Generics could be defined as a strategy to obtain code reusability by defining generic courses, interfaces, constructors and methods that can be utilized with totally different knowledge varieties and in addition achieve sort security by declaring the info sort being used in the implementation before-hand, subsequently eliminating the probabilities of a run-time error.

How are generics carried out in Java?

Generics are carried out using angular brackets “<>”. The brackets enclose the sort parameter “T” inside them. Instance,. The sort parameter “T” is a place holder which signifies that a knowledge sort will probably be assigned to it at run time. For example, a generic class might be defined as:

public class MyGenericClass

The next are the standard sort parameters:

  • T: Sort
  • E: Factor
  • N: Number
  • Okay: Key
  • V: Worth

S, U, V and so forth are used to outline second, third and fourth parameters respectively in case multi-parameter are getting used.

Understanding Generics in Java

By now you could be wondering what is sort safety and how does it work? Or how are generic courses, interfaces, constructors and methods any totally different from our common courses and strategies that make them reusable? Let’s discover out.

Java being a statically typed language requires you to declare the “type” that is the info sort of the value being held by the variable before utilizing it.

Example: String myString =”eduCBA”;

Here “String” is the info sort, “myString” is the variable that may hold a worth whose sort is String.

Now, should you try to move a Boolean value in place of a string, for example:

String myBooleanStr = true;

You will immediately get a compile-time error stating “Type mismatch: cannot convert from boolean to String”.

Generics ( compile-time error)

How can we obtain code reusability with generics?

Now, allow us to define a daily technique:

public static void welcome(String identify)
System.out.println(“welcome to ” + identify);

This technique may be invoked only by passing a string parameter. For instance:


Its output shall be “welcome to eduCBA”.

Nevertheless, you can’t invoke this technique bypassing some other knowledge varieties comparable to integer or boolean. In the event you attempt to try this, you’ll be prompted with a compile-time error stating “The method welcome(String) in the type Runner is not applicable for the arguments (boolean)”. Which means you can’t move another knowledge sort to a way which solely accepts a string as a parameter.

Generics(accepts a string as a parameter)

This also means for those who wish to invoke an analogous technique for a special knowledge sort then you will have to write a new technique that accepts the required knowledge sort as a parameter. This function of re-writing methods with parameters of various knowledge varieties is also referred to as technique overloading. The key disadvantage of this is it will increase the dimensions of your code.

Nevertheless, we might also use Generics to re-write the above technique and use it for any knowledge sort we require.

Defining a Generic technique:

public static void welcome(T t)
System.out.println(“it is ” + t);

Notice: Here “t” is an object of sort T. T might be assigned the info sort that is being used to invoke the tactic.

Now you possibly can reuse this technique by invoking it for a string when required or a boolean or an integer or another knowledge sort.

Integer Myint = 1;

The above statements will present the under output:

It is Educa
It is 1
That is true

Subsequently, through the use of generics right here we’re capable of re-use our technique for different knowledge varieties.

Generics (different data types)

How can we obtain sort safety utilizing Generics?

One of the main differences between Arrays and Collection is that Arrays can retailer solely homogeneous knowledge, whereas Collections can store heterogeneous knowledge. That is Collections can store any user-defined knowledge sort/ objects.

NOTE: Collections can solely maintain objects (user-defined knowledge sort) and never a primitive knowledge sort. So as to work with primitive knowledge, sort collections make use of wrapper courses.

Now, let us think about an ArrayList.

ArrayList myList = new ArrayList();

Let us add knowledge of sort String, Integer and Double to the ArrayList object.


On printing the ArrayList object we will see that it holds the following values: [eduCBA, 1, 5.2].

Generics in Java (e ArrayList object)

Now for those who wish to retrieve these values into variables then, you will want to typecast them.

String someStr = (String)myList.get(zero);
Integer someInt = (Integer)myList.get(1);
Double someFlt = (Double)myList.get(2);

In case you do not typecast, you’ll be prompted with a compile-time error stating “Type mismatch: cannot convert from Object to String”.

compile-time error

From this, you possibly can conclude that while retrieving the objects out of your ArrayList, you’ll want to typecast it to their respective varieties. The question that arises here is how will you realize which knowledge sort to typecast it to? In actual time your ArrayList will include hundreds of document and typecasting it to totally different knowledge varieties for each individual object won’t be an choice. You may find yourself typecasting it to the improper knowledge sort. What occurs then?

This time you will not get a compile time error however will throw a runtime error stating “Exception in thread “main” java.lang.ClassCastException: java.lang.Integer cannot be forged to java.lang.String at com.serviceClasess.Runner.primary(”.

runtime error stating

Since we will’t guarantee the kind of knowledge current inside a set (in this case ArrayList), they’re thought-about not protected to use with respect to sort. This is the place generics come into play to offer sort security.

Using ArrayList with Generics:

ArrayList myList = new ArrayList();

Discover that inside angular brackets “<>”, String sort is specified which suggests this specific implementation of ArrayList can solely maintain String sort knowledge. In the event you attempt to add another knowledge sort to it, it should merely throw compile time error. Right here you might have made your ArrayList type-safe by eliminating its probability of adding a unique knowledge sort aside from “String”.

angular brackets

Now that you’ve specified the info sort that is allowed to be added to your collection with the help of generics, you not have to typecast it while retrieving your knowledge. That is you possibly can simply retrieve your knowledge by writing:

String someStr = myList.get(zero);

    data by writing

How does Generics in Java make working so easy?

It helps make your collections sort protected thus ensuring your code doesn’t fail at a later level on account of a run time exception. It also saves the coder from having to typecast every object in the collection making the code improvement quicker and simpler. By making use of generic courses and methods one also can reuse the code as per ones required knowledge sort during implementation.

What else are you able to do with Generics in Java?

Up to now we’ve got seen how we will achieve sort security and code reusability with generics. Now allow us to take a look at the other options generics provide. They’re:

  1. Bounded & a number of bounded varieties
  2. Sort wildcards

Bounded Sort: In case of a bounded sort the info sort of a parameter is bounded to a specific vary. This is achieved with the assistance of the “extends” keyword.

For Instance, allow us to contemplate a generic class with a bounded sort parameter that extends Runnable interface:

class myGenericClass

Now, whereas creating its object in another class:

myGenericClass myGen = new myGenericClass();

The above statement will execute completely with none errors. That is in case of the bounded sort you’ll be able to cross the identical class sort or its youngster class sort. Also, you possibly can bind the parameter sort to an interface and cross its implementations when invoking it, as in the case of our instance above.

What happens in case you attempt to use another sort of parameter?

myGenericClass myGen = new myGenericClass();

In the above case, you’ll get a compile-time error stating “Bound mismatch: The type Integer is not a valid substitute for the typecast of the type myGenericClass”.

bounded type 9

Multiple bounded varieties: In case of multiple bounded varieties we will bind the parameter knowledge sort to multiple sort. For example,

Class myGeneric

On this case, you’ll be able to move any sort which extends Number class and implements Runnable interface. Nevertheless, when using multiple bounded varieties few things ought to be noted:

  1. We can’t prolong multiple class at a time.
  2. We will prolong any variety of interfaces at a time that is there is no limit for interfaces.
  3. The class identify should all the time come first adopted by the interface identify if not it’ll end result in a compile-time error.

Sort Wildcards: They’re represented by “?” – question mark image.  It makes use of two important key phrases:

extends (to outline higher sure) and tremendous (to define decrease bounds).

For example,

ArrayList al

This ArrayList object “al” will hold any knowledge of sort T and all its subclasses.

ArrayList al

This ArrayList object “al” will hold any knowledge of sort T and all its superclasses.

Benefits of Generics in Java

1. Flexibility: Generics offers our code with the pliability to accommodate totally different knowledge varieties with the help of generic courses and methods.

2. Code Maintenance and Reusability: As a result of generic courses and methods one needn’t re-write the code, in case of a change in requirements at a later stage making the code easier to take care of and reuse.

three. Sort safety: Supplies sort security to the gathering framework by defining the info sort the collection can maintain beforehand and eliminating any probabilities of failure at run time as a result of ClassCastException.

4. Eliminating the need to typecast: Because the knowledge varieties being held by the collections are already determined one need not typecast it at the time of retrieval. This reduces the size of the code and in addition reduces a coder’s effort.

Generics in Java expertise

As a way to work with Generics, you have to be properly versed with the basics of Java. You must understand how sort checking and sort casting works. Thorough information of other concepts comparable to technique overloading, the relationship between dad or mum and youngster courses, interfaces and their implementations are crucial. Also understanding the distinction between primitive knowledge varieties (system outlined knowledge sort) and objects (user-defined knowledge sort) is essential on the subject of working with the collection framework.

Why should we use Generics in Java?

Utilizing generics makes our code more maintainable because it reduces the need to rewrite knowledge sort particular code every time there is a change in requirement. Through the use of generics bounded sort you possibly can prohibit the info sort and at the similar time provide flexibility to your code by defining its vary. Your code is less more likely to fail at a later point as it offers sort security making your code much less error-prone.

Scope for Generics in Java

Generics scope is restricted to compile time. Meaning generics concept is relevant only at compile time however not at run time. For Example,

ArrayList myList = new ArrayList();

ArrayList myList = new ArrayList();

ArrayList myList = new ArrayList();

ArrayList myList = new ArrayList();

Right here all of the above four statements are one and the same. They may permit the addition of any sort of knowledge to the listing object.


Generics makes coding straightforward for a coder. It diminishes the probabilities of encountering ClassCastException at run time by offering robust type-checking. Utterly eliminates the need for sort casting which suggests less code must be written. Offers us with the feasibility to develop generic algorithms which might be unbiased of the info sort they’re working with.

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