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Java > Learn Java > why can't we create an object for abstract class? why...
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why can't we create an object for abstract class? why wait,notify,notifyall methods were in object class but not in thread class?

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Java/J2EE Trainer

The Generalized object can be a abstract class in the sense. Consider we have three object Employee, Manager, and Engineer we can establish the relationship like Manager extends Employee , Engineer extends Employete like that. When we create polymorphic object like Employee jo hn= null; john = new...
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The Generalized object can be a abstract class in the sense. Consider we have three object Employee, Manager, and Engineer we can establish the relationship like Manager extends Employee , Engineer extends Employete like that. When we create polymorphic object like Employee jo hn= null; john = new Manager(); //later john = new Engineer(); Now I can say "john" is polymorphic object just think now. this statement Employee john = new Employee(); it is not a meaningful what we going to do with top level Employee object but I can say Employee john = new Manager() or Employee john = new Engineer.. So the better OO Principle is the generalized class or object or entity can be a abstract class. in this case Employee can be abstract class. read less
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Abstract class is having an abstract method. It is empty method, created for future requirements, therefore usage is not certain by specifying objects to it.
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Abstract by its meaning points to something not concrete or not not.defined, same with java. In java abstract means a class or a method that can be either defined or leave it abstract to be overridden by the child class..for example if we have a Car as a class with methods like brake(),accelrate() defined...
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Abstract by its meaning points to something not concrete or not not.defined, same with java. In java abstract means a class or a method that can be either defined or leave it abstract to be overridden by the child class..for example if we have a Car as a class with methods like brake(),accelrate() defined but we will have to leave getColor() as abstract because we dont know or cant define one color for all cars so that makes class Car as abstract since.some of its.details will be defined or rather better implemented by its child classe and hence instantiating a class with incomplete behavior doesnt make sense therefore abstract classes cannot be instantiated. The methods wait,notify and notifyAll work on the object on which the thread has obtained a lock on hence when the task is complete on that object it is the objects duty to notify the thread to release the lock or notify other threads about its completion.or status...hence these methods are in object and since.Object is global parent class in Java i.e. parent class.of every class by default, and therefore these methods are available in Thread class as well read less
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Assistant Professor With 2 Yrs Experience

To explain this in one sentence, "An abstract class has a protected constructor (by default) allowing only derived types to initialize it." What would happen when you call an abstract method? There would be no actual implementation of the method to invoke. So, the CLI would reject it.
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Assistant Professor With 2 Yrs Experience

To putting your query in a single statement "An abstract class has a protected constructor (by default) allowing derived types to initialize it." Without a derived type where would the data go? What would happen when you call an abstract method? There would be no actual implementation of the method to...
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JAVA J2EE trainer

We create an Abstract class in JAVA when we do not want to instantiate an Object. We do this when we are not sure of the implementation of all the methods in the class or we simply do not want to instantiate it. Most classic example is Shape and it's subclasses Rectangle, Triangle etc. Here for some...
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We create an Abstract class in JAVA when we do not want to instantiate an Object. We do this when we are not sure of the implementation of all the methods in the class or we simply do not want to instantiate it. Most classic example is Shape and it's subclasses Rectangle, Triangle etc. Here for some method area(), implementation will be different for all sub classes and for the superclass Shape we may not know it's implementaion. So we can simply mark that method abstarct and so the class is also Abstract. For exact implentation rules, you can check many tutorials available. And so it becomes comparable to an Interface. For your second question, please note the methods wait(), notify() and soforth are always applied on the state of the Object and not the Thread that is why they are present in Object class and not Thread class. read less
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Java Tutor 6 years of IT Industry Experience

Abstract classes are not complete classes, hence we cant not create an object of Abstract classes. Wait, Notify and NotifyAll methods are in Object class to serve the purpose of MultiThreading.
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Abstract class is meant for acting the class as a parent. so inorder to restrict the class being used as it is. java has set this rule. but u can still access the instance methods and variable by subclassing the class.
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1. As abstract meaning indicates, Abstract class will have an design prototypes. Ideally declaring all methods prototypes and Class need to implement those methods which are extending the Abstract class. suppose 2 classes extending the abstract class and both classes implementing all abstract methods....
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1. As abstract meaning indicates, Abstract class will have an design prototypes. Ideally declaring all methods prototypes and Class need to implement those methods which are extending the Abstract class. suppose 2 classes extending the abstract class and both classes implementing all abstract methods. if java allows to create the object of abstract class then compiler will gets ambiguity which method need to class since 2 classes extending abstract class due to this reason Java does not allow to create the object for abstract class to make the design is simple. 2. Initial basic understanding is wait, notify and notifyAll methods are used for inter-thread communication. Synchronize key is used for mutual exclusion. In multithreading environment threads will communicate each other. In order to avoid race condition we will use Synchronize keyword. Reasons for wait and notify methods are part of object class as listed below. 1. locks are made available on object instead of threads . 2. Threads will wait for lock or hold lock but we dont know which thread is waiting for lock instead it know waiting on which object. 3. Object class is the right place to keep all these methods wait, notify, any thread can communicate with another thread by using locks (waiting on object) by using wait and notify methods. read less
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Computer Software, Training, Corporate Training

Hi Jilani, Tom be very simple and short.... Any Object (not just a thread) can be the monitor for a thread. The wait and notify are called on the monitor. The running thread checks with the monitor. So the wait and notify methods are in Object and not Thread
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