The Object class is inherently the superclass for all classes in Java, serving as the highest class in the Java hierarchy.
Utilizing the Object class can be advantageous when referencing an object of unknown type. It is important to understand that a reference variable of a parent class can point to an object of a child class, a concept known as upcasting.
Consider, for instance, a scenario where there exists a method named getObject which is designed to provide an object of varying types such as Employee or Student. In such cases, one can utilize a reference of the Object class to point to the specific object. As an illustration:
Object obj=getObject();//we don't know what object will be returned from this method
The Object class offers various shared functionalities to all objects, including the ability to compare, clone, and notify objects.
Methods of Object class
| The Object class provides many methods. They are as follows: |
|---|
| Method | Description |
|---|---|
| public final Class getClass() | returns the Class class object of this object. The Class class can further be used to get the metadata of this class. |
| public int hashCode() | returns the hashcode number for this object. |
| public boolean equals(Object obj) | compares the given object to this object. |
| protected Object clone() throws CloneNotSupportedException | creates and returns the exact copy (clone) of this object. |
| public String toString() | returns the string representation of this object. |
| public final void notify() | wakes up single thread, waiting on this object's monitor. |
| public final void notifyAll() | wakes up all the threads, waiting on this object's monitor. |
| public final void wait(long timeout)throws InterruptedException | causes the current thread to wait for the specified milliseconds, until another thread notifies (invokes notify() or notifyAll() method). |
| public final void wait(long timeout,int nanos)throws InterruptedException | causes the current thread to wait for the specified milliseconds and nanoseconds, until another thread notifies (invokes notify() or notifyAll() method). |
| public final void wait()throws InterruptedException | causes the current thread to wait, until another thread notifies (invokes notify() or notifyAll() method). |
| protected void finalize()throws Throwable | is invoked by the garbage collector before object is being garbage collected. |
We will have the detailed learning of these methods in next chapters.