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The $exists is used to check whethre a filed exists, whereas $ne is for not equal condition. Let us first create a collection with documents −> db.existsDemo.insertOne({"Name":"Chris", "Age":21}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7c3916d78f205348bc650") } > db.existsDemo.insertOne({"Name":"", "Age":null}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7c39a6d78f205348bc651") } > db.existsDemo.insertOne({"Name":null, "Age":24}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7c3a66d78f205348bc652") } > db.existsDemo.insertOne({"Age":23}); { "acknowledged" : true, "insertedId" : ObjectId("5cd7c3c36d78f205348bc653") }Following is the query to display all documents from a collection with the help of find() method −> db.existsDemo.find().pretty();This will produce the following output −{ "_id" : ObjectId("5cd7c3916d78f205348bc650"), "Name" : "Chris", "Age" : 21 } { "_id" : ObjectId("5cd7c39a6d78f205348bc651"), "Name" : "", "Age" ... Read More
Removing duplicatesTo remove duplicates in an array we have many logical methods, but advanced javascript has provided some methods so that the task of removing duplicates has become very simple. Some of those methods are set() and filter(). For better understanding lets' discuss each method individually.Set()The important use of the set() method is that it only allows unique values. In other words, it will automatically remove duplicates and makes the task easy for us. The Set() method won't take any logical approach in removing duplicates.Example In the following example, the duplicates in the provided array have been removed without any ... Read More
Using loops in programming languages we can execute a set of statements repeatedly. Java provides various loops namely while loop, for loop and the do while loop.The for statement contains an initialization statement, a condition and, an increment or decrement operation.Initializing statement − The initialization determines the starting value of the loop.Condition − The condition in for loop is a statement returning a boolean value. This condition determines the exit value of the loop. It is executed before the statements of the loop.Increment and decrement − Using this the loop will be incremented or decremented to the next value.After initializing ... Read More
To select the first item in JList, use setSelectionInterval() method:String values[]= { "One", "Two", "Three", "Four", "Five", "Six"}; JList list = new JList(values); int begn = 0; int end = 0; list.setSelectionInterval(begn, end);The following is an example to select the first item in JList:Examplepackage my; import java.awt.event.*; import java.awt.*; import javax.swing.*; class SwingDemo extends JFrame { static JFrame frame; static JList list; public static void main(String[] args) { frame = new JFrame("JList Demo"); SwingDemo s = new SwingDemo(); JPanel panel = new JPanel(); String values[]= ... Read More
The Copy initialization can be done using the concept of copy constructor. As we know that the constructors are used to initialize the objects. We can create our copy constructor to make a copy of some other object, or in other words, initialize current object with the value of another object. On the other hand, the direct initialization can be done using assignment operation.The main difference between these two types of initialization is that the copy initialization creates a separate memory block for the new object. But the direct initialization does not make new memory space. It uses reference variable ... Read More
This example demonstrate about How to create a local Notifications in AndroidStep 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.Step 2 − Add the following code to res/layout/activity_main.xml. Step 3 − Add the following code to src/MainActivity.package app.tutorialspoint.com.notifyme ; import android.app.NotificationChannel ; import android.app.NotificationManager ; import android.os.Bundle ; import android.support.v4.app.NotificationCompat ; import android.support.v7.app.AppCompatActivity ; import android.view.View ; public class MainActivity extends AppCompatActivity { public static final String NOTIFICATION_CHANNEL_ID = "10001" ; private final static String default_notification_channel_id = "default" ... Read More
You can use distinct() to get the equivalent of select distinct. Let us first create a collection with documents −> db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"John", "Age":23}); { "acknowledged" : true, "insertedId" : ObjectId("5cd12759e3526dbddbbfb60b") } > db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Larry", "Age":25}); { "acknowledged" : true, "insertedId" : ObjectId("5cd12768e3526dbddbbfb60c") } > db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"David", "Age":25}); { "acknowledged" : true, "insertedId" : ObjectId("5cd12773e3526dbddbbfb60d") } > db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Carol", "Age":26}); { "acknowledged" : true, "insertedId" : ObjectId("5cd1277ee3526dbddbbfb60e") } > db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Sam", "Age":25}); { "acknowledged" : true, "insertedId" : ObjectId("5cd12793e3526dbddbbfb60f") } > db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Larry", "Age":25}); { "acknowledged" : true, "insertedId" : ObjectId("5cd127a3e3526dbddbbfb610") } > db.distinctNameAndAgeDemo.insertOne({"ClientFirstName":"Carol", "Age":26}); ... Read More
Memory cycleRegardless of the programming language, the memory cycle is almost same for any programming language. There are 3 steps in a memory life cycle1) Allocation of memory .2) use the allocated memory(reading or writing)3) Release the allocated memory when it is unnecessary.The first and last parts are directly connected in low-level languages but are indirectly connected in high-level languages such as JavaScript.1) Allocation of memory in javascriptJavaScript is called garbage collected language, that is when variables are declared, it will automatically allocate memory to them.When there are no more references for the declared variables, allocated memory will be released. ExampleIn the ... Read More
For this, create JOptionPane.QUESTION_MESSAGE and with the user action display individual messages, for example −int res = JOptionPane.showOptionDialog(new JFrame(), "Do you like Cricket?", "Hobbies", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE, null, new Object[] { "Yes", "No" }, JOptionPane.YES_OPTION); if (res == JOptionPane.YES_OPTION) { System.out.println("Selected Yes!"); }Above, we have displayed a message on console if the user will selects YES button. The following is an example to make JOptionPane to handle Yes, No and Closed buttons −Examplepackage my; import javax.swing.JFrame; import javax.swing.JOptionPane; public class SwingDemo { public static void main(String args[]) { int res = JOptionPane.showOptionDialog(new JFrame(), "Do you like ... Read More
To combine multiple rows into a comma delimited list, use the GROUP_CONCAT() method. Let us first create a table −mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Name varchar(30), Marks int ); Query OK, 0 rows affected (0.52 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(Name, Marks) values('John', 67); Query OK, 1 row affected (0.25 sec) mysql> insert into DemoTable(Name, Marks) values('Carol', 69); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable(Name, Marks) values('Sam', 69); Query OK, 1 row affected (0.12 sec) mysql> insert ... Read More