Nested Class:

A class written inside another class is known as nested class, and the class that contains the inner class is called the outer class.

Nested class are of two types Static class and  Non-static inner class. And non-static nested class are known as Inner class.

Syntax of Nested class:

    class OuterClass{  
     //code .... 
     class InnerClass{  
      //code ....  
     }  
    }  

Inner Class:

A class that is written inside a class but outside a method is known as inner class. Inner class can be private but it cannot be accessed from an object outside that class.

Example:

class OuterClass{
   int num;
   //inner class
   private class InnerClass{{
      public void print(){	   
      System.out.println("This is an inner class");
      }
   }
   //Accessing he inner class from the method within
   void displayInner(){
      InnerClass inner = new InnerClass();
      inner.print();
   }
}
   
public class Iclass{
   public static void main(String args[]){
      //Instantiating the outer class 
      OuterClass out=new OuterClass();
      //Accessing the displayInner() method.
      out.displayInner();
   }

}

It will print output :

This is an inner class