When to extend and when to create object

[chaitanya karthikk]

Hi everybody, I am Chaitanya, I have a doubt regarding when to extend a class and when to create object for a class and use it.

Suppose I am having a billing application and there are many input fields asking the user to enter the values such as mobile number, price, name, quantity. Like these I am having many input windows. So what I did is, I created a method for each type of input filed.

One method for validating input fields such as mobile number, quantity. One for validating mobiles, one for validating price etc.

Whenever I want to validate these fields I am simply creating object for the class.

Can anyone tell me about this, thank you all in advance.

[Seetharaman Venkatasamy]

Make all the validate method as static/utility methods .

[chaitanya karthikk]

Seetharaman Venkatasamy wrote:Make all the validate method as static/utility methods .

Hi Venkataswamy, can you please tell me somewhat detailed.

Thank you in advance.

[Nandini Bhaduri]

It will be like

public class ValidateInput {

	
	public static boolean isValidMobileNumber(String mobileNumber)
	{
		// your logic for validating mobile number
		
		return true;
	}
	
	public static void main(String[] args) {
		
		//to validate
		
		if(ValidateInput.isValidMobileNumber("09712037123"))
		{
			//.....
		}
		else
		{
			//.....
		}

	}

}

[chaitanya karthikk]

Hi @ Nandini,

I dint't ask about static methods and how to use them, I asked why should I make it static, there are many classes in my application and each class will have input fields, so I create a class(Validate.java) which consists all these methods to validate different input fields, your code only works for the class which has main function or the main class

My question is should I extend the Validate.java class or should I create an object for it?

Thank you all in advance.

[Wouter Oet]

I would not use a static approach because then you'll lose the polymorphic abilities and thus you're going to need a lot of classes. About the question "My question is should I extend the Validate.java class or should I create an object for it?" Those are 2 completely different things. Extending is adding or specializing behaviour and creating an Object is invoking an constructor which results in a new Object being created. I'm going to assume that you meant to say "create a new Class for it". I would go for extending provided that there is common ground (i.e. an Date validator should not extend a String validator). This way you can program to an interface/superclass and not specialized implementations.

[Nandini Bhaduri]

chaitanya, i just had the main method in it for testing. of course you can use it from any other class.

[chaitanya karthikk]

Hi Mr.Wouter, I understood the concept you were explaining somewhat, I will describe you a scenario where I will extend and create object depending on the situation.

Suppose that I am having a class called Validate which consists the methods for validating a mobile number, email ID, price, user name.

I will create an object for the Validate class in the classes in which input fields need to be validated.

class NewUser extends JFrame
{
Validate valid=new Validate();
...
...
...
}

class Bill extends JFrame
{
Validate valid=new Validate();
...
...
...
}

Now for suppose in one class I want to validate an email ID, but the domain names must be only gmail, yahoo, aol etc. So I can't use the validate email Id method of Validate class, so what I will do is I will create another class named ValidateExtended which extends Validate class

class ValidateExtended extends Validate
{
//override validateEmail(String email)
{
}
}

Now I ll create object for ValidateExtended class where I want to use the second type of validateEmail(String) method.

Is my approach right one?

Thank you all in advance.

[chaitanya karthikk]

Is there anyone? Is my approach right or wrong?

[Paul Clapham]

It's wrong.

I say that because you named the class "ValidateExtended". If you can't think of a good name for the class, but you just have to say that it extends some other class, then it must be the case that you didn't have a good reason for extending it. Normally the reason for extending the class would provide a suitable name for the class.

In general the answer to the question "Should I extend a class" is "It depends". Followed by a discussion of the options available in the case you had in mind. In the case you described it's quite possible that extending the Validate class might be the correct option.

[chaitanya karthikk]

Thank you Paul, seems I am going in the right direction. :thumbup: