Comments can be used to explain Java code, and to make it more readable. It can also be used to prevent execution when testing alternative code.
Single-line comments start with two forward slashes (//).
Any text between // and the end of the line is ignored by Java (will not be executed). Continue reading Java Comments
You can also use the println() method to print numbers.
However, unlike text, we don’t put numbers inside double quotes:
System.out.println(3);
System.out.println(358);
System.out.println(50000);
You learned from the previous chapter that you can use the println() method to output values or print text in Java:
System.out.println("Hello World!");
In the previous chapter, we created a Java file called Main.java, and we used the following code to print “Hello World” to the screen:
Main.java
public class Main {
public static void main(String[] args) {
System.out.println("Hello World");
}
}
Some PCs might have Java already installed.
To check if you have Java installed on a Windows PC, search in the start bar for Java or type the following in Command Prompt (cmd.exe):
C:\Users\Your Name>java -version
If Java is installed, you will see something like this (depending on version):
java version "22.0.0" 2024-08-21 LTS Java(TM) SE Runtime Environment 22.9 (build 22.0.0+13-LTS) Java HotSpot(TM) 64-Bit Server VM 22.9 (build 22.0.0+13-LTS, mixed mode)
If you do not have Java installed on your computer, you can download it for free at oracle.com. Continue reading Java Getting Started
Java is a popular programming language, created in 1995.
It is owned by Oracle, and more than 3 billion devices run Java.
It is used for:
To limit the result in MongoDB, we use the limit() method.
The limit() method takes one parameter, a number defining how many documents to return.
Consider you have a “customers” collection: Continue reading Python MongoDB Limit
You can update a record, or document as it is called in MongoDB, by using the update_one() method.
The first parameter of the update_one() method is a query object defining which document to update.
Note: If the query finds more than one record, only the first occurrence is updated.
The second parameter is an object defining the new values of the document. Continue reading Python MongoDB Update
You can delete a table, or collection as it is called in MongoDB, by using the drop() method.
Delete the “customers” collection:
import pymongo
myclient = pymongo.MongoClient("mongodb://localhost:27017/")
mydb = myclient["mydatabase"]
mycol = mydb["customers"]
mycol.drop()
The drop() method returns true if the collection was dropped successfully, and false if the collection does not exist. Continue reading Python MongoDB Drop Collection
To delete one document, we use the delete_one() method.
The first parameter of the delete_one() method is a query object defining which document to delete.
Note: If the query finds more than one document, only the first occurrence is deleted.