abstract & Object Class

abstract class

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Object class

Java defines one special class called Object that is an implicit superclass of all other classes.

NOTE

A reference variable of type Object can refer to an object of any other class. Object var;

Object defines the following methods, which means that they are available in every object:

Object clone( )  
//Creates a new object that is the same as the object being cloned.


boolean equals(Object object)
//Determines whether one object is equal to another.


void finalize( )
//Called before an unused object is recycled. (Deprecated by JDK 9.)


int hashCode( )
// Returns the hash code associated with the invoking object.


Class<?> getClass( ) 
// Obtains the class of an object at run time.


void notify( )
// Resumes execution of a thread waiting on the invoking object.


void notifyAll( )
// Resumes execution of all threads waiting on the invoking object.


String toString( )
// Returns a string that describes the object.


void wait( ) 
void wait(long milliseconds)
void wait(long milliseconds, int nanoseconds)
// Waits on another thread of execution.

The methods getClass( ), notify( ), notifyAll( ), and wait( ) are declared as final. You can override the others.

equals( ) method compares two objects. It returns true if the objects are equal, and false otherwise.

toString( ) method returns a string that contains a description of the object on which it is called. Also, this method is automatically called when an object is output using println( ).

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