This question already has answers here:
The difference between Classes, Objects, and Instances
(16 answers)
Closed 4 years ago.
What is the definition of a Class , Object and an Instance and what is the difference between an Instance and an Object.
I would like my answer in Simple English
Class is collection of various objects, variables, functions etc.
class DemoClass {
void method(){
......
}
}
When you want to create a new instance of a class you need to create a new object of that class.
DemoClass dc = new DemoClass();
You can then access this instance (methods etc. of this instance) from the object you created.
dc.method();
Related
This question already has answers here:
what is the Class object (java.lang.Class)?
(7 answers)
Closed 2 years ago.
Recently I was learning annotations in java and came across Reflection API and a part of its code was:
Meta obj = new Meta();
//Get a Class object
CLass<?> c = obj.getClass();
The thing that I am not able to understand is that what is the difference between object obj and object c since both of them are just class objects.
You could treat Class object as metadata of normal object. Moreover, when you get obj.getClass() e.g. for different Integer objects, you'll get the smae Class object.
This question already has answers here:
What is a StackOverflowError?
(16 answers)
Closed 4 years ago.
I have designed a GUI which has a jTextArea. I can append text to this very easily in this class. But I would also like to append text to this from methods of other classes.
For this I make the jTextArea public and create an object of that class in the other class. Now I can write to the jTextArea while executing methods in the other classes.
But it turns out that I need a method of the class I created an object in within my GUI class as well. As I do that, StackOverflowError happens. What should I do?
Instead of initializing the BTDBattlesBot object with a new keyword in AutomatedActions class, you can add a parameterized constructor which takes BTDBattlesBot object as parameters and initialize the object in this constructor. Something like below
public class AutomatedActions {
...............
private final BTDBattlesBot botWindow = null;
// Below is the parametrized constructor
public AutomatedActions(BTDBattlesBot botWindow) {
botWindow = this.botWindow;
}
..........
}
Then in the BTDBattlesBot class, while creating the object of AutomatedActions class, instead of calling the default constructor, call the newly created parametrized constructor and pass the current object of BTDBattlesBot class using this keyword. By doing this you should be able to achieve what you want
class BTDBattlesBot {
......
AutomatedActions action = new AutomatedActions(this);
......
}
This question already has answers here:
Difference between object and instance
(15 answers)
What exactly is an instance in Java?
(12 answers)
Closed 8 years ago.
In Java, what is the difference between instance of a class and Object of a class.
For a class A, Take a look :
line 1 : A a; // Declaring a reference variable of class A
Line 2 : a = new A();// Instantiating an object of class A ( An object/instance is created
on Right hand side of the equation)
So....can the line 2 also be : // Instantiating an instance of class A
which mean Instance and Object are absolutely the same thing ?
Please give an objective answer than subjective.
.So an instance and object is same ? No difference at all. An object is an instance of the class .... or an Instance is an object of a class....both are same ?
For all intents and purposes, object and instance can be used interchangeably, but the accepted answer at this link will give you a good understanding of how you should use the two:
Difference between object and instance
Yes, I'd agree that "instance" and Object are the same thing.
1 : A a; // Declaring a reference variable of class A
2 : a = new A();// Instantiating an object of class A
3 : Object o = a; // a is also an object
All instances in Java are also Objects, so they're the same thing. That's an is-a relationship. You can say that any instance in Java is-a Object. Objects are a type (class), and you can make instances of just type Object alone if you want.
Object x = new Object();
Classes are also objects.
4 : Class<A> atype = a.getClass();
5 : Object otype = atype;
So objects (instances) have-a Class, and classes are objects too. I think this is why things are so murky, all these words bear a very close relationship. Note all the things on the left hand side are also called reference types.
This question already has answers here:
The difference between Classes, Objects, and Instances
(16 answers)
Closed 8 years ago.
There can only be one instance of class and can have many objects...? If not then can you please explain me difference between Instance and Object of the class
Instance and object of class are same things.
Theoratically Instance represents certain object at one time.
Example: Suppose you have Employee Class(Structure) with firstName and lastName
your instance or object(Value) represent Employee with firstname "Sanjay" and lastname "Rabari"
This question already has answers here:
Use of TypeLiteral in java
(5 answers)
Closed 9 years ago.
There is an ASTNode subclass called TypeLiteral.
The description of this type of code says that it looks like
( Type | void ) . class
I don't believe I have ever seen anything like this.
Can anyone provide an example of a TypeLiteral, and perhaps additionally of it being used in a Java program?
There is a class called Class that represents the class of an object. It contains various useful methods for introspection on that class and objects of that class. One way to get a class object is to use the Object method getClass(). But if you want to refer to a Class by name of its class, you use a class literal.
Some examples:
class Foo {
void method(Object b) {
if(b.getClass() == Foo.class) {
Foo f = Foo.class.cast(b);
}
Foo.class.getResourceAsStream(...);
Foo.class.getMethod("method", Object.class);
}
}