Saturday, April 20, 2019

Java 8 - Optional


Java 8 - Optional

In this blog, I’ll discuss about Optional class which was introduced in JDK8 under java.util.package. Optional class is used to represent a value is present or absent.

With Optional class, developers have to less worry about NullPointerException and can work on neat and clean code. It contains at most one value.


Advantages:
· No need to check for null
· No more NullPointerException at runtime

Public final class Optional<T> extends Object {
}
Let’s understand all its usage with the help of example

1. Optional.empty()

To create an empty Optional object we simply need to write

// How to create empty Optional
             Optional<String> optional = Optional.empty();
             System.out.println("1. Optional: " + optional);
    Output:
            1. Optional: Optional.empty


2. isPresent()

You can also check whether any value present in Optional or not
          System.out.println("2. Optional: " + optional.isPresent());
Output:
          2. Optional: false

3. Of() method

We can also use Static Of method to create an Optional Object.
      //Can create Optional using Static Of method
      Optional<String> name = Optional.of("WaheedTechblog.com");
      System.out.println("3. Name: " + name.toString());
Output:
       3. Name: Optional[WaheedTechblog.com]

Note: Make sure you are not passing any null value to Of() method else it would throw a NullPointer Exception.

Optional<String> nullValue = Optional.of(null);
             System.out.println("4. Name: " + nullValue.toString());
Output:
             Exception in thread "main" java.lang.NullPointerException
       at java.base/java.util.Objects.requireNonNull(Objects.java:221)
       at java.base/java.util.Optional.<init>(Optional.java:107)
       at java.base/java.util.Optional.of(Optional.java:120)
       at com.waheedtechblog.optional.OptionalExample.main(OptionalExample.java:20)

4. OfNullable()

If you are not sure about the object you must use OfNullable API.

       //Can accept NUll value as well
       Optional<String> isNull = Optional.ofNullable("WaheedTechblog.com");
       System.out.println("5. Name: " + isNull.toString());
Output:
       5. Name: Optional[WaheedTechblog.com]

If we pass a null reference, it does not throw an exception but returns an empty Optional object.


5. isPresent()

We can use isPresent() method to check whether the Optional object is empty or contains some value.

Optional<String> isNull = Optional.ofNullable("WaheedTechblog.com");
       //check isNull object contains some value
       if(isNull.isPresent()) {
                    System.out.println("6. Optional object contains some value: " + isNull.toString());
             }
Output:
       6. Optional object contains some value: Optional[WaheedTechblog.com]


6. isEmpty()

Similarly , we can use isEmpty method to check whether the Optional object is empty or not

//Check whether object is empty or not
             Optional<String> nullValue = Optional.ofNullable(null);
             if (nullValue.isEmpty()) {System.out.println("7. Is Optional empty? " + nullValue.toString());
       }
Output:
7. Optional object contains some value: Optional.empty


7. ifPresent()
It enables us to run some code if Optional Object is not empty. Most of the time, we normally do something like this in our application.
 If(user != null) {
       String name = user.getName();
}
Over here, we are performing some operation based on if condition. This approach is lengthy and there are chances to miss such null checks which can result in a NullPointerException at runtime.

ifPresent() accepts Consumer functional Interface.

//Execute if Optional object exist.
             Optional<String> name = Optional.of("WaheedTechblog.com");
             name.ifPresent(value -> System.out.println("8. Length of name: " + value.length()));
Output:
8. Length of name: 18


8. orElse()

We can use orElse() method to set some default value incase if Optional object is Empty.

      //Set Default value if Object is empty
             String nullString = null;
             String testOrElse = Optional.ofNullable(nullString).orElse("This is default value");
             System.out.println("9. Print testorElse value: " + testOrElse);
Output:
9. Print testorElse value: This is default value


9. orElseGet()

This API is very similar to orElse() method except that instead of taking default value, you can pass Supplier functional interface which returns response based on some operation.

//Invoke Functional Interface if Optional Object is empty
String testOrElseGet = Optional.ofNullable(nullString).orElseGet(() -> "waheedtechblog");
             System.out.println("10. Print orElseGet value: " + testOrElseGet);
Output:
            10. Print orElseGet value: waheedtechblog

Note: At the very first glance, it looks like orElse and orElseGet method are very similar and either one of them can be used to get the default value but this is not very true. There is a subtle but very important difference between the two.

Let’s understand this with Example
       private String getDbConnection() {
             System.out.println("13. Invoking Default fucntion");
             return "Create db Connection";
       }

// Checking the diff between orElse Vs orElseGet
String testOrElseDiff = Optional.ofNullable("waheedtechblog").orElse(optionalExample.getDbConnection());
             System.out.println("11. Print testorElse value: " + testOrElseDiff);

String testOrElseGetDiff = Optional.ofNullable("waheedtechblog").orElseGet(optionalExample::getDbConnection);
System.out.println("12. Print orElseGet value: " + testOrElseGetDiff);

Output:
13. Invoking Default fucntion
11. Print testorElse value: waheedtechblog
12. Print orElseGet value: waheedtechblog


If you observe the output, you will realize that orElse() method is invoking getDBConnection() when the object is already present whereas orElseGet() method is not invoking the DB call.

So, I would suggest choose orElseGet over orElse as database query or any rest API call can cost to your application performance when there was no need of that.

10. orElseThrow()

Instead of calling any default method in case of Optional value not present, it throws an exception.

//Throw runtime exception if Optional value is not present
      String orElseThrowTest = Optional.ofNullable(nullString).orElseThrow(RuntimeException::new);
Output:
Exception in thread "main" java.lang.RuntimeException
       at java.base/java.util.Optional.orElseThrow(Optional.java:408)
       at com.waheedtechblog.optional.OptionalExample.main(OptionalExample.java:62)

11. get()

Get returns the value of Optional Object if not null or else throws no such element exception.
Optional<String> getTest = Optional.ofNullable("waheedtechblog");
      System.out.println("15. GetTest value: " + getTest.get());
Output:
        15. GetTest value: waheedtechblog

Note: get throws NoSuchElementException if Optional object is empty


12. Filter()

The concept of filter is very similar to stream API filter. It takes Predicate as an argument and returns an Optional object.

// filteration on Optional
             Optional<String> username = Optional.of("waheedtechblog");
boolean isLengthValid = username.filter(str -> str.length() > 5).isPresent();
             System.out.println("16. is Length Valid: " + isLengthValid);
 Output:
       16. is Length Valid: true

13. map()

Using map, we can transform the Optional value.

        // map to perform operation on Optional
        Optional<String> password = Optional.of("waheedtechblog");
        String encodedPassword = password.map(str ->                                  Base64.getEncoder().encodeToString(str.getBytes())).get();
System.out.println("17. Encoded Password: " + encodedPassword);

              Output:
            17. Encoded Password: d2FoZWVkdGVjaGJsb2c=


We can also merge filter and map together to get the result.

       // first do validation and then operation on Optional object
       String validatedEncodedPassword = password.filter(ps -> ps.length()
> 15)  .map(str ->  Base64.getEncoder().encodeToString(str.getBytes())).toString();
System.out.println("18. Validated Encoded Password: " + validatedEncodedPassword);

Output:
18. Validated Encoded Password: Optional.empty

Happy Coding…!!!







Friday, April 19, 2019

Java 9 - Try with resources Improvement


Java 9  -  Try with resources Improvement



In this blog, I’ll discuss about try with resources which was introduced with JDK 7 and what enhancement has been done in JDK 9.

Try with resources is a great feature which was introduced in JDK 7 that helps in closing resources automatically after being used.

Any class can be used as resources if that class implements AutoClosable Interface.

Advantages
  • As try with resources closes all the resources file Automatically which prevents memory leaks.
  • More readable code as you don’t have to write unnecessary code. 

Let’s understand it with an example

import java.io.FileNotFoundException;
import java.io.FileOutputStream;

/**
 * This class will explain the try with resources which was introduced with
 * JDK7.
 *
 * @author AbdulWaheed18@gmail.com
 *
 */
public class ExmapleWithJava7 {

       public static void main(String[] args) throws FileNotFoundException {

             try (FileOutputStream fileStream = new FileOutputStream("App.log");) {
                    String logMessage = "[INFO] DATA NEED TO BE WRITTEN";
                    byte logMessageInBytes[] = logMessage.getBytes();
                    fileStream.write(logMessageInBytes);
                    System.out.println("Updated log files.");
             } catch (Exception e) {
                    // handle error
             }
       }
}

With JDK7, we have to declared all resources within try block but which is not possible for every resource like DB connection. To use DB connection, we have to close the resources explicitly in finally block which was an obvious bug.

With the JDK 9 enhancement, you can just pass the reference in try block without declaring within try block.

import java.io.FileNotFoundException;
import java.io.FileOutputStream;

/**
 * This class will explain enhancement of try with resources block which was
 * introduced with JDK9 .
 *
 * @author AbdulWaheed18@gmail.com
 *
 */
public class ExmapleUsingJava9 {

       public static void main(String[] args) throws FileNotFoundException {
             FileOutputStream fileStream = new FileOutputStream("App.log");
             try (fileStream) {
                    String logMessage = "[INFO] DATA NEED TO BE WRITTEN";
                    byte logMessageInBytes[] = logMessage.getBytes();
                    fileStream.write(logMessageInBytes);
                    System.out.println("Updated log files.");
             } catch (Exception e) {
                    // handle error
             }
       }
}

You can download the Source code from here.

Happy Coding…!!!





Sunday, April 7, 2019

Supplier Functional Interface - JAVA 8


Supplier Functional Interface


Supplier is an in-built functional interface introduced in Java 8 in the java.util.function package. Supplier does not expect any input but returns the output. This interface can be handy where you want to generate some data like OTP, currentTime or even GUID
The functional method of Supplier is get(T t).
Here is a simple source code of java.util.function.Supplier

@FunctionalInterface
public interface Supplier<T> {
    /**
     * Gets a result.
     * @return a result
     */
    T get();
}
Where T get () is an abstract method where T is the return type of the function.

Example 1:

import java.util.Date;
import java.util.function.Supplier;

public class SupplierExample {

       public static void main(String[] args) {

             // Calling Supplier Functional Interface without using Lambda Expression
             SystemDate date = new SystemDate();
             System.out.println("System Date: " + date.get());

             // Using Lambda Expression
             Supplier<Date> supplier = () -> new Date();
             System.out.println("Using lambda, System Date: " + supplier.get());
       }

}

class SystemDate implements Supplier<Date> {

       @Override
       public Date get() {
             return new Date();
       }
}

Output:
System Date: Sun Apr 07 17:37:49 IST 2019
Using lambda, System Date: Sun Apr 07 17:37:49 IST 2019


This interface doesn’t contains any default or static method

That’s it for Supplier Functional Interface, Will talk about other Predefined Functional Interface in my next blog.

Happy Coding…!!!