Object Class in Java

Last Updated : 21 Nov, 2025

Object class (in java.lang) is the root of the Java class hierarchy. Every class in Java either directly or indirectly extends Object. It provides essential methods like toString(), equals(), hashCode(), clone() and several others that support object comparison, hashing, debugging, cloning and synchronization.

Why Object Class?

Acts as the root of all Java classes
Defines essential methods shared by all objects
Provides default behavior for printing, comparing and cloning objects
Supports thread communication (wait(), notify(), notifyAll())

Using toString() and hashCode()

Java

class Person{    String n;   // Constructor  public Person(String n) {  this.n = n;  }  // Override toString() for a   // custom string representation  @Override  public String toString() {  return "Person{name:'" + n + "'}";  }  public static void main(String[] args) {    Person p = new Person("Geek");    // Custom string representation  System.out.println(p.toString());    // Default hash code value  System.out.println(p.hashCode());   } }

Output

Person{name:'Geek'} 321001045

Explanation: In the above example, we override the toString() method to provide a custom string representation of the Person class and use the hashCode() method to display the default hash code value of the object.

Object Class Methods

Object class provides multiple methods which are as follows:

1. toString() Method

toString() provides a String representation of an object and is used to convert an object to a String.

Java

class Student{    String name = "Vishnu";  int age = 21;  @Override  public String toString(){    return "Student{name='" + name + "', age=" + age + "}";  }  public static void main(String[] args) {  Student s = new Student();    // Calls overridden toString()  System.out.println(s.toString());   } }

Output

Student{name='Vishnu', age=21}

Explanation: Overridden toString() prints a custom readable string for the object

2. hashCode() Method

hashCode() method returns the hash value of an object (not its memory address). Used heavily in hash-based collections like HashMap, HashSet, etc.

Java

class Employee{    int id = 101;  @Override  public int hashCode(){    return id * 31; // Simple custom hash  }  public static void main(String[] args) {  Employee e = new Employee();  System.out.println(e.hashCode());  } }

Output

Explanation: hashCode() returns an integer value used in hashing-based collections like HashMap. If two objects are equal, they must produce the same hash code..

3. equals(Object obj) Method

equals() method compares the given object with the current object. It is recommended to override this method to define custom equality conditions.

Java

class Book{    String title;  Book(String title) {  this.title = title;  }  @Override  public boolean equals(Object obj){    Book b = (Book) obj;  return this.title.equals(b.title);  }  public static void main(String[] args) {  Book b1 = new Book("Java");  Book b2 = new Book("Java");  System.out.println(b1.equals(b2)); // true  } }

Output

true

Explanation: equals() compares objects based on content rather than reference. Must be overridden when custom comparison logic is needed.

4. getClass() method

getClass() method returns the class object of "this" object and is used to get the actual runtime class of the object.

Java

public class Geeks{    public static void main(String[] args)  {  Object o = new String("GeeksForGeeks");  Class c = o.getClass();  System.out.println("Class of Object o is: "  + c.getName());  } }

Output

Class of Object o is: java.lang.String

Explanation: The getClass() method is used to print the runtime class of the "o" object.

5. finalize() method

finalize() method is invoked by the Garbage Collector just before an object is destroyed. It runs when the object has no remaining references. You can override finalize() to release system resources and perform cleanup, but its use is discouraged in modern Java.

Java

public class Geeks {  public static void main(String[] args) {    Geeks t = new Geeks();  System.out.println(t.hashCode());  t = null;  // calling garbage collector  System.gc();  System.out.println("end");  }  @Override protected void finalize()  {  System.out.println("finalize method called");  } }

Output

1510467688 end finalize method called

Explanation: The finalize() method is called just before the object is garbage collected.

6. clone() method

clone() method creates and returns a new object that is a copy of the current object.

Java

class Student implements Cloneable{    int id = 1;  String name = "Vishnu";  @Override  public Object clone() throws CloneNotSupportedException{    return super.clone(); // shallow copy  }  public static void main(String[] args) throws Exception{    Student s1 = new Student();  Student s2 = (Student) s1.clone();  System.out.println(s1.name); // Vishnu  System.out.println(s2.name); // Vishnu  } }

Output

Vishnu Vishnu

Explanation: clone() creates a copy of the current object (shallow copy by default). Class must implement Cloneable or else it throws CloneNotSupportedException.

7. Concurrency Methods: wait(), notify() and notifyAll()

These methods are related to thread Communication in Java. They are used to make threads wait or notify others in concurrent programming.

Java

import java.io.*; public class Book implements Cloneable {  private String t; // title  private String a; // author  private int y; // year  public Book(String t, String a, int y)  {  this.t = t;  this.a = a;  this.y = y;  }  // Override the toString method  @Override public String toString()  {  return t + " by " + a + " (" + y + ")";  }  // Override the equals method  @Override public boolean equals(Object o)  {  if (o == null || !(o instanceof Book)) {  return false;  }  Book other = (Book)o;  return this.t.equals(other.getTitle())  && this.a.equals(other.getAuthor())  && this.y == other.getYear();  }  // Override the hashCode method  @Override public int hashCode()  {  int res = 17;  res = 31 * res + t.hashCode();  res = 31 * res + a.hashCode();  res = 31 * res + y;  return res;  }  // Override the clone method  @Override public Book clone()  {  try {  return (Book)super.clone();  }  catch (CloneNotSupportedException e) {  throw new AssertionError();  }  }  // Override the finalize method  @Override protected void finalize() throws Throwable  {  System.out.println("Finalizing " + this);  }  public String getTitle() { return t; }  public String getAuthor() { return a; }  public int getYear() { return y; }  public static void main(String[] args)  {  // Create a Book object and print its details  Book b1 = new Book(  "The Hitchhiker's Guide to the Galaxy",  "Douglas Adams", 1979);  System.out.println(b1);  // Create a clone of the Book object and print its  // details  Book b2 = b1.clone();  System.out.println(b2);  // Check if the two objects are equal  System.out.println("b1 equals b2: "  + b1.equals(b2));  // Get the hash code of the two objects  System.out.println("b1 hash code: "  + b1.hashCode());  System.out.println("b2 hash code: "  + b2.hashCode());  // Set book1 to null to trigger garbage collection  // and finalize method  b1 = null;  System.gc();  } }

Output

The Hitchhiker's Guide to the Galaxy by Douglas Adams (1979) The Hitchhiker's Guide to the Galaxy by Douglas Adams (1979) b1 equals b2: true b1 hash code: 1840214527 b2 hash code: 1840214527

Explanation: The above example demonstrates the use of toString(), equals(), hashCode() and clone() methods in the Book class.