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java lang Object Class

java lang Object Class

java.lang.Object Class

Object Class in Java

Java Object class is the root of the class hierarchy. Every class has Object as a super class. All objects, including arrays, implement the methods of this class.

What is java.lang.Object in Java ?

The java.lang.Object is a class in Java . This is the root of the class hierarchy . Object class is present in java.lang package . Every class in Java is directly or indirectly derived from the java.lang.Object class . If a Class does not extend any other class then it is direct child class of Object . the Object class methods are available to all Java classes . Hence Object class acts as a root of inheritance hierarchy in any Java Program .

What is a class object in Java ?

An object is the instance of the class , which helps programmers to use variables and methods from inside the class . A class is used to bind data as well as methods together as a single unit . object acts as a variable of the class . Classes have logical existence. Objects have a physical existence .

How do you create a class object in Java ?

In Java , the new keyword is used to create new objects .

  1. Declaration − A variable declaration with a variable name with an object type .
  2. Instantiation − The 'new' keyword is used to create the object .
  3. Initialization − The 'new' keyword is followed by a call to a constructor .

What is object type in Java ?

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 , known as up casting .

What are the common behaviors of all the objects in Java ?

The Object class provides some common behaviors to all the objects such as object can be compared , object can be cloned , object can be notified etc .

What is Java object hashCode ?

Returns a hash code value for the object . Whenever it is invoked on the same object more than once during an execution of a Java application , the hashCode method must consistently return the same integer , provided no information used in equals comparisons on the object is modified .

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

What is getClass () in Java ?

The java.lang.Object.getClass() method returns the runtime class of an object. That Class object is the object that is locked by static synchronized methods of the represented class.

How do you compare objects in Java ?

In Java equals() method is used to compare equality of two Objects . The equality can be compared in two ways: Shallow comparison: The default implementation of equals method is defined in java.lang.Object class which simply checks if two Object references (say x and y) refer to the same Object .

Why object class is superclass of all classes in Java ?

All classes in Java by default extend the Object class , that's why Object is superclass of every class in Java . Class Object is the root of the class hierarchy . All objects , including arrays , implement the methods of this class .

How do you clone an object in Java ?

The clone() method of Object class is used to clone an object . The java.lang.Cloneable interface must be implemented by the class whose object clone we want to create . If we don't implement Cloneable interface , clone() method generates CloneNotSupportedException . The clone() method is defined in the Object class .

What is the Difference Between Class and Object ?

Class and Object are the essential part of Object Oriented Programming ( OOP ) . A class can be considered as a construct which encapsulates a group of variables and methods . An object acts as a member or instance of that class .

What are the Differences Between Class and Object in Java ?

Following are the differences between Class and Object in Java .

Class Object
A class is a blueprint from which you can create the instance, i.e. objects . An object is the instance of the class , which helps programmers to use variables and methods from inside the class .
A class is used to bind data as well as methods together as a single unit . object acts as a variable of the class .
Classes have logical existence . Objects have a physical existence .
A class doesn't take any memory spaces when a programmer creates one . An object takes memory when a programmer creates one .
The class has to be declared only once . Objects can be declared several times depending on the requirement .

What are the java.lang.Object class methods in Java ?

The java.lang.Object provides a number of methods that are common to all objects . The toString() is the most common such method . Since the default toString() method only produces the name of the class . java.lang.Object Class methods helps to perform the various operations like clone objects , compare objects , get the class name of the object . Following are the List of java.lang.Object Class Methods or functions .

Modifier and Type Method Description
protected Object java.lang.Object.clone() Creates and returns a copy of this object .
boolean java.lang.Object.equals(Object obj) Indicates whether some other object is "equal to" this one .
protected void java.lang.Object.finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object .
Class<?> java.lang.Object.getClass() Returns the runtime class of this Object .
int java.lang.Object.hashCode() Returns a hash code value for the object . For every object , JVM generates a unique number which is hashcode . It returns distinct integers for distinct objects . Override of hashCode() method needs to be done such that for every object we generate a unique number .
void java.lang.Object.notify() Wakes up a single thread that is waiting on this object's monitor .
void java.lang.Object.notifyAll() Wakes up all threads that are waiting on this object's monitor .
String java.lang.Object.toString() Returns a string representation of the object . Whenever we try to print any Object reference , then internally toString() method is called .
void java.lang.Object.wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object .
void java.lang.Object.wait(long timeout) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object , or a specified amount of time has elapsed .
void java.lang.Object.wait(long timeout, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object , or some other thread interrupts the current thread , or a certain amount of real time has elapsed .

Following Java Object class example you can learn how to use Java Object class.

java.lang.Object Class Example

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/*  Java Object class example
    Save with file name ObjectExample1.java */
  
public class ObjectExample1
{
  public static void main(String args[])
  {
    //Java Object CLASS DECLARATION
    Object obj;
    //CREATE INSTANCE FOR Java Object CLASS
    obj = new Object();
    //Java Object CLASS OUTPUT
    //NOTHING TO WORRRY THERE IS NO VALUE
    //IT PRINTS SOME CODE
    System.out.println("Object value : " + obj);
  }
}

java.lang.Object Class Example 2

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/*  Java Object Class Example with String Class
    Save with file name ObjectExample2.java */
  
public class ObjectExample2
{
  public static void main(String args[])
  {
    //String CLASS DECLARATION
    String s;
    //CREATE INSTANCE FOR String CLASS
    s = new String("Huda Tutorials");
    //Java Object CLASS DECLARATION
    Object obj;
    //TYPECAST String CLASS INSTANCE TO
    //Java Object CLASS INSTANCE
    obj = (Object) s;
    //Java Object CLASS OUTPUT
    System.out.println("Object value : " + obj);
    //IT RETURNS RUNTIME CLASS OF THIS OBJECT
    //java.lang.String
    System.out.println("Object Class : " + obj.getClass());
  }
}
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