Lambda Expression : Replacement of Anonymous Inner Class

Lambda Expression:

·       A new feature of java8s

·       Main intension is replacement of anonymous inner class.

·       Lambda expression is nothing but an anonymous method(method without name)

The general form is :

(para-list)->

{

   //method body

};

Let's see an example for better clarity using normal interface approach, then using anonymous inner class approach, then lambda expression approach:

Approach-1:

package java8s;

interface Transaction

{

   public void withDraw(int amt);

}

class A implements Transaction

{

   public void withDraw(int amt)

   {

       System.out.println("amount withdrawn is"+amt);

   }

}

public class LambdaExpressionExample {

   public static void main(String[] args) {

      

       A ob1=new A();  

      

       ob1.withDraw(15000);

      

   }

}

Approach-2:

package java8s;

interface Transaction

{

   public void withDraw(int amt);

}

public class LambdaExpressionExample {

   public static void main(String[] args) {

      

       Transaction ob1=new Transaction()   //Anonymous Inner Class

       {

          public void withDraw(int amt)

          {

              System.out.println("amount withdrawn is"+amt);

          }

       };

      

       ob1.withDraw(15000);

      

   }

}

Approach-3:

package java8s;

interface Transaction

{

   public void withDraw(int amt);

}

public class LambdaExpressionExample {

   public static void main(String[] args) {

       Transaction ob1=(int amt)->

          {

              System.out.println("amount withdrawn is"+amt);

          };

ob1.withDraw(1500);

       

   }

}

Output:

amount withdrawn is1500

Sorting Collections with Java Lambdas

In Java, the Comparator class is used for sorting collections. In the following examples, we will sort a list of players based on name, surname, name length and last name letter. We will first sort them as we did before, using anonymous inner classes, and then reduce our code using lambda expressions.

In the first example, we will sort our list by name. Using the old way, this looks like this:

String[] players = {"Avijit", "Chintu", "Akshay", "Santosh", "Ritesh", "Avisek", "Krushna", "Surya", "Rudra", "Biswajit"};

// Sort players by name using anonymous innerclass

Arrays.sort(players, new Comparator<String>() {

       @Override

       public int compare(String s1, String s2) {

              return (s1.compareTo(s2));

       }

});

With lambdas, the same thing can be achieved like this:

// Sort players by name using lambda expression

Comparator<String> sortByName = (String s1, String s2) -> (s1.compareTo(s2));

Arrays.sort(players, sortByName);

// or this

Arrays.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));

Java - Why are interface variables static and final by default?

Interface variables are static because Java interfaces cannot be instantiated in their own right; the value of the variable must be assigned in a static context in which no instance exists. The final modifier ensures the value assigned to the interface variable is a true constant that cannot be re-assigned by program code.

public: for the accessibility across all the classes, just like the methods present in the interface

static: as interface cannot have an object, the interfaceName.variableName can be used to reference it or directly the variableName in the class implementing it.

final: to make them constants. If 2 classes implement the same interface and you give both of them the right to change the value, conflict will occur in the current value of the var, which is why only one time initialization is permitted.

Also all these modifiers are implicit for an interface, you dont really need to specify any of them.

Can we define variables in interface in Java?

In Java , interface doesn't allow you to declare any instance variables. Using a variable declared in an interface as an instance variable will return a compile time error. You can declare a constant variable, using static final which is different from an instance variable.

How Java Lambdas Expressions affect the code in simple way

Let us start with some basic examples. Here, we will see how lambda expressions affect the code in a simple way. Having a list of players, the “for loop”, as programmers often refers to the for statement, can be translated in Java SE 8 as below:

String[] s1 = {"Anant", "Nilan", "Dolagobinda", "Babu", "Rupeli", "Sanjay", "Akshay", "Santosh"};

List<String> players =  Arrays.asList(s1);

      

// Old looping

for (String player : players) {

     System.out.print(player + "; ");

}

      

// Using lambda expression and functional operations

players.forEach((player) -> System.out.print(player + "; "));

// Using double colon operator in Java 8

players.forEach(System.out::println);

What is JAVA Lambda Expression???

Java Lambda expressions are a new and important feature included in Java SE 8. A lambda expression provides a way to represent one method interface using an expression. A lambda expression is like a method, it provides a list of formal parameters and a body (which can be an expression or a block of code) expressed in terms of those parameters.

Lambda expressions also improve the Collection libraries. Java SE 8 added two packages related to bulk data operations for Collections, the java.util.function package, and the java.util.stream. A stream is like an iterator, but with a lot of extra functionality. Taken together, lambda expressions and streams are the biggest change to Java programming since the generics and annotations were added to the language. 

How to sort ArrayList in JAVA

CollectionSort.java package java8s; import java.util.*; public class CollectionSort {           public static void main(String... args)           {                        List l = new ArrayList();                        l.add("Bhubaneswar");                        l.add("Cuttack");                        l.add("Paradeep");                        l.add("Jagatsinghpur");                        l.add("Kujanga");                        Collections.sort(l);                                                     System.out.println("Location : "+l);                                        } }

Output

Location : [Bhubaneswar, Cuttack, Jagatsinghpur, Kujanga, Paradeep]

How to avoid duplicate values from JAVA List / ArrayList

Hiii frnds, this is a nice question in interview forum, so let's see how to remove duplicate objects from List / ArrayList

ArrayListExample.java

package java8s;

import java.util.*;

public class ArrayListExample {

     public static void main(String[] args) {

          ArrayList al=new ArrayList();

          al.add("first");

          al.add("second");

          al.add("third");

          al.add("first");

          al.add("first");

         

          ArrayList al1=new ArrayList(new LinkedHashSet(al));

         

          Iterator it=al1.iterator();

          while(it.hasNext())

          {

              System.out.println(it.next());

          }

     }

}

Output

first

second

third

GET vs. POST in Servlet

	GET	POST
1.	It is used for getting information from the server side	It is used to post the information to the server.
2.	It performs read-only operation	It performs update/write operation.
3.	Whatever the request can be sent that is append with URL	Whatever request send to the server that is not exposed in the URL
4.	Only text or character type of data can be sent	Any type of data can be send
5.	Limited amount of data can be send (up to 2KB)	No length limit of data that we can send
6.	It provides less security because the user’s request is directly exposed in URL bar. Hence, sensitive  information is not recommended to be send.	It provides high security
7.	Bookmarking is possible which is the advantage	Bookmarking is not possible
8.	Caching is also possible which is also another advantage of get method	Caching is not possible