Help with objects, classes, etc...

Question

Im having a little trouble grasping the concept of all of these names. I know that every Java program is a class. Now, is a method what we call in C++ a function? It seems as though this is what it is while reading this book but just want to clarify it. And also, what is a good defninition for an object. I know that parseInt() is an object but does that mean that is is some kind of function/method that was declared or made in a class?

Answer 1

lol ... ok; it's easy to get caught up in the jargon...
A class is a "type" of thing, complete with values which describe the thing and operations that the thing can perform. For instance, a "dog" can be described in terms of its breed, size, markings, and things that it does (eat, do tricks, bark, etc).
An object is a dinstinct instance of a class. So, if you are talking about one particular dog, let's say Lassie, you can describe it as a collie, of a certain size, etc, etc.
Object oriented programming makes use of this jargon. The act of creating an object from a class description is known as "instantiation".
You mentioned C++. In C++, you can have functions which stand alone, or functions which are part of classes. C++ functions which are part of class definitions are known as "member functions"; Java methods are like C++ member functions.
now, on to parseInt(). remember how we said that a class definition can define operations (like "eat", for a dog)? well, although we can define the eat operation, only a instance of dog (e.g., Lassie) can actually perform the operation. so, if you have Lassie and RinTinTin in front of you, and you say, "Lassie, bark!", only Lassie will perform that operation.
in object oriented programming, a method which makes sense for one object (that is, one particular instance of a class) to perform is known as an instance method. there's another abstraction, though... you can define variables and methods which belong to all instances of a class (as a group), rather than any one particular object. These are known as class variables and class methods, and Java uses the keyword "static" to identify them.
So, if I had the class dog, it might look a little like:
public class Dog {
    private float weight;  // each dog object will have its own weight variable
    static private int count;  // this is shared by all instantiated dog objects!
    public void bark() {
        // instance method.  call this with respect to a particular dog object
        System.out.println ("Woof.");
    public static int getCount() {
        // this method is shared by all instantiated dog objects.  It's called using the syntax
        // Dog.getCount(), rather than by instantiating a dog object and using the object to call
        // the method
        return count;
// etc...
}Does that make sense? some variables belong to each particular instantiated object, while others don't need an object in order to refer to them.
one more thing: in Java, there are objects and there are primitives. the primitives are data types such as int, float, boolean, etc. Java also provides wrappers for these primitives, so you can refer to them in object contexts; for example, Integer, Boolean, etc.
OK... now back to your question. parseInt() is a static method of class Integer. (therefore, you don't need an instance of Integer in order to call parseInt().
the parseInt() method returns an int.
make sense?