Why method of java must be implemented in the class definition itself?

Answer 1

I think that the reason this question has not been answered is because nobody understands the question!!! What exactly are you asking???

So, I will try to answer the question, but only in a very general sort of way.

Let's create an example class called "Jonny."

The bear minimum of creating the class Jonny would be the following:

public class Jonny{

}

This text would, of course, need to be saved in a file named Jonny.java, and would be compiled into the Jonny class.

Now, if we are going to get into methods, lets start with a simple constructor:

public class Jonny

{

public Jonny()

{

}

}

Now, to the slightly trained eye, this statement is basically the same as the original without the constructor, because Java automatically provides you with a default empty constructor.

The great thing about constructors, however, is that we can use them to allow fast initializations of Objects (Which every object extends). So we can allow the user of our new class to create a Jonny with other parameters as well.

Let's make a Jonny extend JFrame, and then allow the user to initialize the frames name within the constructor:

public class Jonny extends JFrame{

public Jonny(String frameName)

{

this.setTitle(frameName);

}

}

Wow, that wasn't too hard was it.

I suspect that this is the method you were speaking of when asking this question, so the answer is that it is not really a "method," but is actually a CONSTRUCTOR, which creates the object itself. We can create actual methods as well within our new class, though:

public class Jonny extends JFrame{

public Jonny(String frameName)

{

this.setTitle(frameName);

}

public void showTheThingAlready()

{

this.pack();

this.setVisible(true);

}

}

So there you have it. The answer is that it is not a method, but a constructor. It is not required to explicitly have a constructor, but they can be very useful when dealing with new objects. I often allow myself to have several different constructors, allowing me different ways to create objects and initiallize them at the same time. It is a fairly common practice in Java to have many methods named the same thing as well, but with different types of input parameters.

I hope I have answered your question.

James

Answer 2

Well, where do you want to put your methods? You can still have external libraries which have static methods you can call, if you are looking to just write a function.

Answer 3

All Java methods belong to a class. This is just the way the language is designed. Besides, if any method were to be written outside of a class, you would have no way to reference it.