Introduction

• Class class in Java is part of the Reflection API and is used to represent the runtime metadata of a class or interface.
• It is present in the java.lang package and is denoted as java.lang.Class<T>.
• It allows you to get information about the class such as its fields, methods, constructors, modifiers, superclass and interfaces.
• Objects of Class type are created automatically by JVM when a class is loaded.

Different Ways to get the Class object:

• There are mainly three ways to get the Class object:
  1. Using Class.forName("fully.qualified.ClassName")
  2. Using object.getClass()
  3. Using ClassName.class

• 1. Program Using Class.forName("fully.qualified.ClassName")

  public class MainApp
  {
      public static void main(String[] args) throws Exception
      {
          // Getting Class object using Class.forName()
          Class<?> c = Class.forName("java.lang.String");
  
          System.out.println("Class Name : " + c.getName());
          System.out.println("Is Interface : " + c.isInterface());
          System.out.println("Superclass : " + c.getSuperclass());
      }
  }

  Output:

  Class Name : java.lang.String
  Is Interface : false
  Superclass : class java.lang.Object

• 2. & 3. Program Using object.getClass() and Using ClassName.class

  public class MainApp
  {
      public static void main(String[] args)
      {
          // ------ Using getClass() ------
          String str = "Hello";
          Class<?> c1 = str.getClass();
          System.out.println("Class from getClass(): " + c1.getName());
  
          // ------ Using .class ------
          Class<?> c2 = String.class;
          System.out.println("Class from .class: " + c2.getName());
      }
  }

  Output:

  Class from getClass(): java.lang.String
  Class from .class: java.lang.String

Important Methods of Class class

• Some important methods of Class class are as follows:

  S.No	Method	Use
  1	getName()	Returns the fully qualified name of the class.
  2	getSimpleName()	Returns the simple name of the class without package name.
  3	getSuperclass()	Returns the superclass of the class.
  4	getInterfaces()	Returns an array of interfaces implemented by the class.
  5	getDeclaredFields()	Returns all fields (including private) declared in the class.
  6	getDeclaredMethods()	Returns all methods (including private) declared in the class.
  7	getDeclaredConstructors()	Returns all constructors (including private) declared in the class.
  8	getModifiers()	Returns the modifiers (public, private, abstract, etc.) of the class as an int.
  9	isInterface()	Checks if the Class object represents an interface.
  10	isArray()	Checks if the Class object represents an array type.
  11	newInstance()	Creates a new instance of the class (no-arg constructor only).
  12	getPackage()	Returns the package of the class.
  13	getDeclaredAnnotations()	Returns annotations present on the class.

• Program:

  import java.lang.reflect.*;
  
  class Employee
  {
      public String name;
      private int salary;
  
      public Employee() {}
  
      public Employee(String name, int salary)
      {
          this.name = name;
          this.salary = salary;
      }
  
      public void work()
      {
          System.out.println(name + " is working");
      }
  
      private void secret()
      {
          System.out.println("Secret salary is: " + salary);
      }
  }
  
  public class MainApp3
  {
      public static void main(String[] args)
      {
          Class<?> clazz = Employee.class;
  
          // Print basic information
          System.out.println("Class Name: " + clazz.getName());
          System.out.println("Simple Name: " + clazz.getSimpleName());
          System.out.println("Superclass: " + clazz.getSuperclass().getName());
  
          // Print interfaces
          System.out.println("\n------ Interfaces ------");
          for (Class<?> i : clazz.getInterfaces())
          {
              System.out.println(i.getName());
          }
  
          // Print fields
          System.out.println("\n------ Declared Fields ------");
          for (Field f : clazz.getDeclaredFields())
          {
              System.out.println(f.getName() + " : " + f.getType().getSimpleName());
          }
  
          // Print methods
          System.out.println("\n------ Declared Methods------");
          for (Method m : clazz.getDeclaredMethods())
          {
              System.out.println(m.getName());
          }
  
          // Print constructors
          System.out.println("\n------ Declared Constructors ------");
          for (Constructor<?> c : clazz.getDeclaredConstructors())
          {
              System.out.println(c);
          }
      }
  }

  Output:

  Class Name: Employee
  Simple Name: Employee
  Superclass: java.lang.Object
  
  ------ Interfaces ------
  
  ------ Declared Fields ------
  name : String
  salary : int
  
  ------ Declared Methods------
  secret
  work
  
  ------ Declared Constructors ------
  public Employee()
  public Employee(java.lang.String,int)