Object class Supermost class in java inherited by all classes

Posted by Gyan Guide on April 7th, 2017

Object class in java is the super most class in java.Every class in java directly or indirectly inherit the Object class.

The Object class is the parent class of all the classes in java by default. In other words, it is the topmost class of java.

The Object class is beneficial if you want to refer any object whose type you don't know. Notice that parent class reference variable can refer the child class object, know as upcasting.

Object class is present in java.lang package. Every class in Java is directly or indirectly derived from the Object class.java course in bangalore

If a Class does not inherit any other class then it is direct child class of Object classand if inherits other class then it is an indirectly derived. Therefore the Object class methods are available to all Java classes. Hence Object class acts as a root of inheritance hierarchy in any Java Program.

Methods Of Object class:

toString(): toString() provides String representation of an Object and used to convert an object to String .toSting() is overrided by the String class.

Whenever we try to print any Object reference, then internally toString() method is called.

Example :

Employee e = new Employee();

// Below two statements are equivalent

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hashCode(): For every object, JVM generates a unique number which is hashcode. It returns distinct integers for distinct objects.It convert the internal address of object to an integer by using an algorithm. Hash code is used to search object in a collection.

equals(Object obj):This method is mainly used to compare the address of the objects. If we compare the same object it returns true and if we are comparing the different object it returns false because two objects have different address.

When equals() is override by String class then it compare the content of the object.

Integer obj1 = new Integer(2), 
Integer obj2= new Integer(4);

if (obj1.equals(obj2))
    System.out.println("objects are equal");
    System.out.println("objects are not equal");

Output : objects are not equal

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Explanation : In above obj1 and obj2 is the reference variable of two different object. Both objects are having different address so while comparing it returns false.


This method returns the runtime class of this Object.getClass()

The getclassmethod is a final method (cannot be overridden) that returns a runtime representation of the class of this object. This method returns a Class object.

We can use the class Object for a variety of information about the class, such as its name, its superclass, and the names of the interfaces that it implements. The following method gets and displays the class name of an object:

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 void displayClassName(Object obj) 
    System.out.println("The Object's class is " + obj.getClass().getName());

finalize() : This method is called just before an object is garbage collected. It is called by theGarbage Collector on an object when garbage collector determines that there are no more references to the object.

clone(): It returns a new object that is exactly the same as this object.It is used to get the copy of the object.

Notify() :This method wakes up a single thread that is waiting on object's monitor.

NotifyAll():This method wakes up all threads that are waiting on object's monitor.

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Wait() :This method causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for object.

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Gyan Guide

About the Author

Gyan Guide
Joined: February 8th, 2017
Articles Posted: 35

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