Advanced Multi Threading in Java [ Latch ]

CountDown latch is one of the kinds of synchronizer which wait for another thread before performing the tasks or This is used to synchronize one or more tasks by enabling them to wait for the tasks completed by other tasks.  It was introduced in Java 5 along with other CyclicBarrier, Semaphore, CuncurrentHashMap and BlockingQueue. Its somehow like the wait and notify but in the more simpler form and will much less code.

It basically works in the latch principle. Or let us suppose we have a seller who is going to sell 10 (No. of operations) apples. The number of customers may be anything but what the seller is concerned about is the number of apples because when it reaches to 0 he can go home. The seller(Main Thread) will wait for the customers (awaits()). Let's say there are 10 customers(Threads) now who are in the line to buy Apple. When one customer buys that Apple then the number of apple decrease by 1 (countdown()) and another customer will get a chance to buy that apple so on the number of apples goes on decreases and finally become 0. After no apples left in the bucket, the seller can stop selling and go home happily. 

Note:: In CountDown Latch the countdown cannot be reset. 

Let's have a look at Java code::

package com.latch;

import java.util.Random;

import java.util.concurrent.CountDownLatch;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

/**

 * Created by yubraj on 1/16/17.

 */

public class latch {

 public static void main(String[] args) {

  ExecutorService executorService = Executors.newSingleThreadExecutor();

  CountDownLatch countDownLatch = new CountDownLatch(5);

  for (int i = 0; i < 5; i++)

   executorService.execute(new Worker(i, countDownLatch));

  try {

   countDownLatch.await();

  } catch (InterruptedException e) {

   e.printStackTrace();

  }

  System.out.println("All the prerequities are done now the application is ready to run yuppy!!!");

  executorService.shutdown();

 }

}

class Worker implements Runnable {

 private int id;

 private CountDownLatch countDownLatch;

 private Random random;

 public Worker(int id, CountDownLatch countDownLatch) {

  this.id = id;

  this.countDownLatch = countDownLatch;

 }

 @Override

 public void run() {

  dowork();

  countDownLatch.countDown();

 }

 private void dowork() {

  System.out.println("Thread with id " + this.id + " is Running .....");

  try {

   Thread.sleep(1000);

  } catch (InterruptedException e) {

   e.printStackTrace();

  }

 }

}

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Simple use of glide library for display images on android

We know all that memory to store images on mobile is limited, if we have display images using through the bitmap images, it will take lots of memory, which is followed by ultimately memory performance and finally application will be slow.

Yes, we have new image display library call glide. Glide is the perfect and best one to use compared to Picasso and Fresco.

Reasons of using Glide:

1. Recommended by Google and has been used in many Google open source projects.
2. Picasso loads the full-size image (1920x1080 pixels) into the memory and let GPU does the real-time resizing when drawn. While Glide loads the exact ImageView-size (768x432 pixels) into the memory which is a best practice.
3. Glide cache both the full-size image and the resized one. Picasso will cache only single size of image, the full-size one. Glide acts differently, caches separate file for each size of ImageView.
4. GIF (animated image) support.
5. In addition, it also helps preventing an app from popular OutOfMemoryError.

Fresco has huge size of library and cache also. Moreover, app freezes while loading big images from internet into ListView.

While Glide has small size of both library and cache.(Source: Quora)

Here is the pictorial difference between Glide vs Picasso vs Fresco.

Now, How to use Glide to display images on Android, Here is the simple steps,

First you have to introduces dependencies on gradle.

compile 'com.github.bumptech.glide:glide:3.5.2'

and 

On your imageview, please provide this code for display images.

image is image view , depend you requirement, 

In kotlin:

val image = currentView.findViewById(R.id.image) as ImageView

In Java

ImageView image= (ImageView) findViewById(R.id.image)

Now, render the image url on our imageview.

Glide.with(context)

.load(currentVolume.imageUrl)

.into(image)

#HappyCoding #ILoveKotlin

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Different way of creating objects in Java or android

We know ,a class provides the blueprint for objects, so create an object from a class. Here are the some way of creating objects in java or android.

Here are some different ways to create objects in java:

1. Using new keyword
This is the most common way to create an object in java. Almost 99% of objects are created in this way.

 MyObject object = new MyObject();

2. Using Class.forName()
If we know the name of the class & if it has a public default constructor we can create an object in this way.

MyObject object = (MyObject) Class.forName("com.test").newInstance();

3. Using clone()
The clone() can be used to create a copy of an existing object.

MyObject newObject = new MyObject();
MyObject object = (MyObject) newObject.clone();

4. Using object deserialization
Object deserialization is nothing but creating an object from its serialized form.

ObjectInputStream objectInputStream = new ObjectInputStream(anInputStream );
MyObject object = (MyObject) objectInputStream.readObject();

5.Using newInstance() method of Constructor class
Similar to the newInstance() method of a Class, there is one newInstance() method in the java.lang.reflect.Constructor class, which we can use to create objects.

Constructor<User> myObject = User.class.getConstructor();
Employee emplyoeeObject = myObject.newInstance();

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Java Functional Programming: Understanding Predicates

As java 8 introduces the predicate functions, but we may wonder where to use those true/false returning function in our daily programming life. The answer is we can use this in the following scenario:
1. when we have to evaluate the objects from the same class which will result in the true or false.
2. to filter the objects by using some of its variables etc.

lets hack Predicate with some examples:

A. Examining if the object is the intance of the particular class or not: 

/** * Created by yubraj on 1/26/16. */

public class MyClass {
    Predicate<MyClass> predicate1 = (MyClass myclass) -> this.equals(myclass);
    Predicate<MyClass> predicate2 =  this::equals;
    String text1 = "yubraj", text2 = "pokharel";
    public MyClass(String text1, String text2) {
        this.text1 = text1;        this.text2 = text2;    }

    @Override    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyClass myClass = (MyClass) o;
        if (!text1.equals(myClass.text1)) return false;
        return text2.equals(myClass.text2);
    }

    @Override    public int hashCode() {
        int result = text1.hashCode();    
        result = 31 * result + text2.hashCode();
        return result;    }

    public void myMethod(MyClass cl){
        System.out.println("Intance equals : " + predicate2.test(cl));    }

    public static void main(String[] args) {
        MyClass mc = new MyClass("sudhan", "pokharel");
        MyClass mc2 = new MyClass("yubraj", "pokharel");
        mc.myMethod(mc);
        System.out.println("-----------------------------------");
        mc2.myMethod(mc2);
    }

}

Output:
true
true
//because both are the intance of the similar object.



B. Filtering the objects

for male employee who are older then 21 years

lets add this in the Employee Class

public static Predicate<Employee> isAdultMale() {

    return p -> p.getAge() > 21 && p.getGender().equalsIgnoreCase("M");

}

then we can access all the employee who are Male and also more then 21 years by passing method as the variable eg:

public static void main(String[] args){

        Employee e1 = new Employee(1,23,"M","Rick","Beethovan");

        Employee e2 = new Employee(2,13,"F","Martina","Hengis");

        Employee e3 = new Employee(3,43,"M","Ricky","Martin");

        Employee e4 = new Employee(4,26,"M","Jon","Lowman");

        Employee e5 = new Employee(5,19,"F","Cristine","Maria");

        Employee e6 = new Employee(6,15,"M","David","Feezor");

        Employee e7 = new Employee(7,68,"F","Melissa","Roy");

        Employee e8 = new Employee(8,79,"M","Alex","Gussin");

        Employee e9 = new Employee(9,15,"F","Neetu","Singh");

        Employee e10 = new Employee(10,45,"M","Naveen","Jain");

         

        List<Employee> employees = new ArrayList<Employee>();

        employees.addAll(Arrays.asList(new Employee[]{e1,e2,e3,e4,e5,e6,e7,e8,e9,e10}));

                

        System.out.println(filterEmployees(employees, isAdultMale()));

}

Happy Coding :)

References: howtodoinjava, oracle

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