What is the instanceof operator used for in Java?

class Simple{  
  public static void main(String args[]){  
  String str1 = "Educative!";
  
  if (str1 instanceof String) 
    System.out.println("str1 is instance of String"); 
  else
    System.out.println("str1 is NOT instance of String"); 
 }  
} 

class Animal { } 
class Mammal extends Animal { } 
class instanceofTest { 
	public static void main(String[] args) { 
		Mammal mobj = new Mammal();
    Animal aobj = new Animal();
    // Is `child` class instance of `child` class?
		if (mobj instanceof Mammal) 
		  System.out.println("mobj is instance of Mammal"); 
		else
		  System.out.println("mobj is NOT instance of Mammal"); 
    // Is `child` class instance of `parent` class?
		if (mobj instanceof Animal) 
		  System.out.println("mobj is instance of Animal"); 
		else
		  System.out.println("mobj is NOT instance of Animal");	
    
    // Is `parent` class instance of `child` class?
    if (aobj instanceof Mammal) 
		  System.out.println("mobj is instance of Animal"); 
		else
		  System.out.println("mobj is NOT instance of Animal");
	} 
} 

class Animal { 
	String name = "Animal";
} 
class Mammal extends Animal { 
	String name = "Mammal";
} 
class ApplicationTest { 
	public static void main(String[] args) { 
		Animal child = new Mammal(); 
		Animal parent = child; 
		// using instance of to check validity before
    // typecasting
		if(parent instanceof Mammal) { 
			System.out.println("Name of accessed class is: " 
                         + ((Mammal)parent).name); 
		} 
	} 
}