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

1. 'Why can't we create an object for abstract class?' Abstract class do not have any physical existence: Animal - Abstract super class Cat, Dog, Cow - Subclass of 'Animal' You can see Cat, Dog, Cow are roaming around physically but not Animal that way. 2. Why wait, notify, notifyall methods were in object class but not in thread class? If they would be there in the Thread class then in cases where you would create thread using Runnable instance (using object having 'Runnable' implementation) those wait, notify, notifyall methods would not be available - you had to write your own. Since they are defined in the Object class, we could use them in the above scenario today. read less

Everybody says, we can't able to create instance for abstract class because it has one or more abstract methods and incomplete detail of particular functionality. I agree that such functionality don't have complete details so we make those as abstract method and that contained class is abstract. Let's now assume that you not in java world, now think that everything is possible, abstract class can also be instantiated now [ object can be created ]. Take example of Car, which has non-abstract method engine() and brake(), and accelrate() same for all cars and some of abstract methods getCarNo(), getColor() are unique for each car, so we declaring these two class es as abstract class. abstract class Car { private Engine engine; private Break _break; private Accelrater accel; public Engine getEngin() { return this.engine; } public void setEngine(Engine engine) { this.engine = engine; } public Break getBreak() { return this._break; } public void setBreak(Break _break) { this._break = _break; } public Accelrater getAccelrate() { return this.accel; } public void setAccelrate(Accelrater accel) { this.accel = accel; } abstract public void getColor(); abstract public void getCarNo(); } if you now try like these Car car = new Car(); // assume it happens car.setEngine(new Engine() ); // fine ok, car.getEngine(); // fine ok, both can executed because both have body same case with other non-abstract method if you this car.getColor(); car.getCarNo(); // its like you are asking something to car class which that doesn't have When you try to access abstract method using abstract class object, it have only declaration but not definition. For this reason they don't allowed creation of object for abstract class, because some persons like me may try to access such methods if they allowed such things.... Lets take, we can't create object for abstract class but we can hold reference of child class.... why this is allowed, let give some work to mind read less

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

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

Abstract classes are not complete. It does not have complete body i.e. class status is not clear so we cant create object. Compiler prevents the instantiation of such incomplete objects. This class doesn't have an implementation for one or more methods. It means that the jvm doesn't have any direction of what to do in case if someone calls the method which is abstract. Hence, it may be crashed. read less