Tag: #startingcoding

SQL Cheat Sheet

March 31st, 2023
When working on something I don’t work on a lot and I need a reference source I write a cheat sheet.

Here’s a simple SQL query language cheat sheet:

SELECT:

The SELECT statement is used to retrieve data from one or more tables.

Example:
```
SELECT column1, column2 FROM table_name;
```
FROM:

The FROM clause is used to specify the table(s) from which data is to be retrieved.

Example:
```
SELECT column1, column2 FROM table_name WHERE condition;
```
WHERE:

The WHERE clause is used to filter the results of a query based on a specified condition.

Example:
```
SELECT column1, column2 FROM table_name WHERE column3 = 'value';
```
ORDER BY:

The ORDER BY clause is used to sort the results of a query based on one or more columns.

Example:
```
SELECT column1, column2 FROM table_name ORDER BY column1 ASC;
```
GROUP BY:

The GROUP BY clause is used to group the results of a query by one or more columns.

Example:
```
SELECT column1, COUNT(*) FROM table_name GROUP BY column1;
```
HAVING:

The HAVING clause is used to filter the results of a GROUP BY query based on a specified condition.

Example:
```
SELECT column1, COUNT(*) FROM table_name GROUP BY column1 HAVING COUNT(*) > 1;
```
JOIN:

The JOIN clause is used to combine data from two or more tables based on a common column.

Example:
```
SELECT column1, column2 FROM table1 JOIN table2 ON table1.column3 = table2.column4;
```
INNER JOIN:

The INNER JOIN clause is used to combine data from two or more tables based on a common column, returning only the rows that have a match in both tables.

Example:
```
SELECT column1, column2 FROM table1 INNER JOIN table2 ON table1.column3 = table2.column4;
```
LEFT JOIN:

The LEFT JOIN clause is used to combine data from two or more tables based on a common column, returning all rows from the left table and matching rows from the right table.

Example:
```
SELECT column1, column2 FROM table1 LEFT JOIN table2 ON table1.column3 = table2.column4;
```
RIGHT JOIN:

The RIGHT JOIN clause is used to combine data from two or more tables based on a common column, returning all rows from the right table and matching rows from the left table.

Example:
```
SELECT column1, column2 FROM table1 RIGHT JOIN table2 ON table1.column3 = table2.column4;
```
UNION:

The UNION clause is used to combine the results of two or more SELECT statements into a single result set.

Example:
```
SELECT column1 FROM table1 UNION SELECT column1 FROM table2;
```
LIKE:

The LIKE operator is used to search for a specified pattern in a column.

Example:
```
SELECT column1 FROM table_name WHERE column2 LIKE '%value%';
```
IN:

The IN operator is used to match a value against a list of values.

Example:
```
SELECT column1 FROM table_name WHERE column2 IN ('value1', 'value2', 'value3');
```
BETWEEN:

The BETWEEN operator is used to match a value against a range of values.

Example:
```
SELECT column1 FROM table_name WHERE column2 BETWEEN 'value1' AND 'value2';
```
DISTINCT:

The DISTINCT keyword is used to return only unique values in a column.

Example:
```
SELECT DISTINCT column1 FROM table_name;
```
These are some of the most commonly used SQL query language statements and operators. There are many more advanced features and functions available, but this cheat sheet

COUNT:

The COUNT function is used to count the number of rows in a table that meet a specified condition.

Example:
```
SELECT COUNT(*) FROM table_name WHERE column1 = 'value';
```
AVG:

The AVG function is used to calculate the average value of a column.

Example:
```
SELECT AVG(column1) FROM table_name;
```
SUM:

The SUM function is used to calculate the sum of a column.

Example:
```
SELECT SUM(column1) FROM table_name;
```
MAX:

The MAX function is used to find the maximum value in a column.

Example:
```
SELECT MAX(column1) FROM table_name;
```
MIN:

The MIN function is used to find the minimum value in a column.

Example:
```
SELECT MIN(column1) FROM table_name;
```
NULL:

The NULL value represents an unknown or missing value in a column.

Example:
```
SELECT column1 FROM table_name WHERE column2 IS NULL;
```
NOT NULL:

The NOT NULL constraint is used to specify that a column must not contain NULL values.

Example:
```
CREATE TABLE table_name (

    column1 INT NOT NULL,

    column2 VARCHAR(255) NOT NULL

);
```
PRIMARY KEY:

The PRIMARY KEY constraint is used to specify a column or set of columns as the primary key for a table.

Example:
```
CREATE TABLE table_name (

    column1 INT PRIMARY KEY,

    column2 VARCHAR(255)

);
```
FOREIGN KEY:

The FOREIGN KEY constraint is used to specify a relationship between two tables, based on a key column in each table.

Example:
```
CREATE TABLE table1 (

    column1 INT PRIMARY KEY,

    column2 VARCHAR(255)

);

CREATE TABLE table2 (

    column3 INT PRIMARY KEY,

    column4 VARCHAR(255),

    column5 INT,

    FOREIGN KEY (column5) REFERENCES table1(column1)

);
```
INDEX:

The INDEX statement is used to create an index on one or more columns in a table, to improve query performance.

Example:
```
CREATE INDEX index_name ON table_name (column1);
```
These are some of the most commonly used SQL statements and keywords. With this cheat sheet, you should be able to write basic SQL queries and understand the results. However, SQL is a vast and powerful language with many advanced features and functions. I encourage you to continue exploring and learning more about SQL as you work with databases.
Java Collections Framework

March 29th, 2023

Java Collections is a framework that provides a set of interfaces and classes to manage and manipulate groups of objects. Collections are used to store, retrieve, manipulate, and transmit data efficiently. In this blog, we will explore the Java Collections framework in depth and explain the different types of collections and their uses.

Java Collections Framework Hierarchy:

The Java Collections Framework consists of the following main interfaces:

Collection: The Collection interface is the root interface of the Java Collections Framework. It defines the basic operations that are common to all collection types, such as adding, removing, and querying elements.

List: The List interface extends the Collection interface and defines an ordered collection of elements. Elements can be accessed by their index position in the list.

Set: The Set interface extends the Collection interface and defines an unordered collection of unique elements. Duplicate elements are not allowed in a set.

Queue: The Queue interface extends the Collection interface and defines a collection that maintains the order in which elements are added. The Queue interface provides methods for adding, removing, and querying elements.

Map: The Map interface is used to store key-value pairs. Each key in a map is associated with a unique value. The Map interface provides methods for adding, removing, and querying key-value pairs.

Java Collections Framework Implementations:

The Java Collections Framework provides several implementations of the above interfaces:

ArrayList: ArrayList is a class that implements the List interface. It provides an ordered collection of elements that can be accessed by their index position in the list. ArrayList is implemented as a resizable array and is similar to the arrays in C or C++.

LinkedList: LinkedList is another class that implements the List interface. It provides a linked list data structure that allows efficient insertion and removal of elements at any position in the list.

HashSet: HashSet is a class that implements the Set interface. It provides an unordered collection of unique elements. Duplicate elements are not allowed in a HashSet.

TreeSet: TreeSet is another class that implements the Set interface. It provides an ordered collection of unique elements. The elements in a TreeSet are stored in a sorted order.

PriorityQueue: PriorityQueue is a class that implements the Queue interface. It provides a priority queue data structure that maintains the order in which elements are added.

HashMap: HashMap is a class that implements the Map interface. It provides a hash table data structure that stores key-value pairs. HashMap provides fast retrieval of key-value pairs.

TreeMap: TreeMap is another class that implements the Map interface. It provides a sorted map data structure that stores key-value pairs in a sorted order.

In conclusion, Java Collections is a powerful framework that provides a set of interfaces and classes to manage and manipulate groups of objects. The Java Collections Framework is used extensively in Java applications to store, retrieve, manipulate, and transmit data efficiently. By understanding the different types of collections and their uses, you can use the Java Collections Framework to write more efficient and effective Java code.

Here is a visual representation of the Java Collections Framework hierarchy and some of its implementations:

simple example (updating soon)

Iterable (interface)

|

Collection (interface)

/ | \

List (interface) Set (interface) Queue (interface)

/ \ / \ / \

ArrayList LinkedList HashSet Deque (interface) PriorityQueue

|_ ArrayDeque

Map (interface)

|

TreeMap

|

HashMap

This diagram shows that Collection is the root interface of the Java Collections Framework, and it has three sub-interfaces: List, Set, and Queue. Each of these interfaces has several implementations, such as ArrayList and LinkedList for List, HashSet and TreeSet for Set, and PriorityQueue for Queue.

The diagram also shows that Map is another interface of the Java Collections Framework, which has two implementations: TreeMap and HashMap. TreeMap provides a sorted map data structure that stores key-value pairs in a sorted order, while HashMap provides a hash table data structure that stores key-value pairs and provides fast retrieval.

Overall, this visual representation helps to show the relationships between the different interfaces and implementations of the Java Collections Framework.
The Class in Java

March 28th, 2023
Object-oriented programming (OOP) is a programming paradigm that uses objects to represent real-world entities and their interactions. In Java, a class is a blueprint or a template that defines the properties and behavior of an object. In this blog post, we’ll discuss the OOP class in Java in detail, including its syntax, properties, and methods, with examples.

Syntax of a Java class

The syntax of a Java class is as follows:
```
[access_modifier] class ClassName [extends SuperClassName] [implements InterfaceName]
{
  // Fields
  // Constructors
  // Methods
}
```
Access modifier specifies the level of access to the class, and it can be public, protected, or private. ClassName is the name of the class, and it should start with a capital letter. The extends keyword is used to inherit properties and behavior from a parent class or a superclass. The implements keyword is used to implement the methods of an interface.

Properties of a Java class

A Java class can have the following types of properties:
1. Instance variables: These are non-static variables that belong to an object. Each object of the class has its own set of instance variables.
2. Static variables: These are class-level variables that belong to the class rather than an object. They are shared by all objects of the class.
3. Final variables: These are constants that cannot be changed once initialized.
4. Transient variables: These are variables that are not serialized when an object is written to a file.
5. Volatile variables: These are variables that are accessed by multiple threads, and their value is always read from main memory.
Methods of a Java class

A Java class can have the following types of methods:
1. Constructors: These are special methods that are used to create objects of the class. They have the same name as the class and do not have a return type.
2. Instance methods: These are non-static methods that belong to an object. They can access instance variables and can modify their values.
3. Static methods: These are class-level methods that belong to the class rather than an object. They cannot access instance variables and can only access static variables.
4. Getter and setter methods: These are methods used to get and set the values of instance variables.
Example of a Java class

Here’s an example of a Java class that defines a Circle object:
```
public class Circle {
  private double radius;

  public Circle(double radius) {
    this.radius = radius;
  }

  public double getRadius() {
    return radius;
  }

  public void setRadius(double radius) {
    this.radius = radius;
  }

  public double getArea() {
    return Math.PI * radius * radius;
  }

  public double getCircumference() {
    return 2 * Math.PI * radius;
  }
}
```
In this example, the Circle class has one instance variable, radius, which is a double value. The class has a constructor that takes a radius parameter and initializes the radius instance variable. The class also has getter and setter methods for the radius instance variable. Finally, the class has two methods, getArea() and getCircumference(), that return the area and circumference of the circle, respectively.

In conclusion, a class in Java is a blueprint that defines the properties and behavior of an object. It can have instance variables, static variables, final variables, transient variables, and volatile variables, and it can have constructors, instance methods, static methods, getter and setter methods, and other types of methods. Understanding classes is an essential part of object-oriented programming in Java, and it’s important to use them effectively to create well-structured and maintainable code.
What is an Object in Java

March 27th, 2023
In object-oriented programming (OOP), an object is an instance of a class that represents a real-world entity and its interactions. In Java, objects are created from classes, which define their properties and behavior. In this blog post, we’ll discuss objects in Java in detail, including their creation, properties, and methods, with examples.

Creating objects in Java

To create an object in Java, you need to follow these steps:
1. Declare a variable of the class type. For example, to create an object of the Person class, you would declare a variable as follows:
```
Person person;
```
1. Allocate memory for the object using the new keyword. For example:
```
person = new Person();
```
1. Initialize the object’s properties using its constructor or setter methods. For example:
```
person.setName("John");
person.setAge(30);
```
Properties of objects in Java

An object in Java has two types of properties: instance variables and methods. Instance variables are non-static variables that belong to an object, and each object has its own set of instance variables. Methods are functions that define the behavior of the object.

Instance variables can be accessed using dot notation, as shown in the following example:
```
Person person = new Person();
person.setName("John");
System.out.println(person.getName());
```
In this example, we create a new Person object, set its name to “John,” and then print out the value of its name instance variable using the getName() method.

Methods of objects in Java

Methods are used to define the behavior of an object in Java. There are two types of methods: instance methods and static methods. Instance methods are non-static methods that belong to an object and can access its instance variables. Static methods are class-level methods that belong to the class rather than an object and cannot access instance variables.

Here’s an example of an instance method in Java:
```
public class Person {
  private String name;
  private int age;

  public void setName(String name) {
    this.name = name;
  }

  public void setAge(int age) {
    this.age = age;
  }

  public void sayHello() {
    System.out.println("Hello, my name is " + name + " and I am " + age + " years old.");
  }
}
```
In this example, we define a Person class with two instance variables, name and age, and an instance method, sayHello(), that prints out a greeting using the object’s name and age instance variables.

To use this method, we first create a new Person object and set its name and age properties, like this:
```
Person person = new Person();
person.setName("John");
person.setAge(30);
```
Then, we can call the sayHello() method on the object, like this:
```
person.sayHello();
```
This will output the following message:
```
Hello, my name is John and I am 30 years old.
```
In conclusion, objects in Java are instances of classes that represent real-world entities and their interactions. Objects have instance variables and methods, which define their properties and behavior, respectively. To create an object in Java, you need to declare a variable of the class type, allocate memory for the object using the new keyword, and initialize its properties using its constructor or setter methods. Understanding objects is an essential part of object-oriented programming in Java, and it’s important to use them effectively to create well-structured and maintainable code.
Java 1.8 Cheat Sheet

March 24th, 2023
Lambda expressions:

Lambda expressions are a concise way to represent a single method interface using an expression. It is a shorthand syntax for implementing interfaces that have only one method.
```
(parameters) -> expression
```
Example:
```
Arrays.asList("a", "b", "c").forEach(e -> System.out.println(e));
```
Stream API:

Stream API is a new feature introduced in Java 1.8 for processing data in a more efficient and concise way. It allows for filtering, sorting, mapping, and reducing data.

Example:
```
List<String> list = Arrays.asList("apple", "banana", "orange", "pear");

long count = list.stream().filter(e -> e.contains("a")).count();
```
Optional:

Optional is a class introduced in Java 1.8 that can be used to represent null values. It forces the programmer to handle null values in a more explicit way.

Example:
```
Optional<String> optional = Optional.ofNullable(null);

String value = optional.orElse("default");
```
Default methods in interfaces:

Default methods in interfaces are methods that have an implementation in the interface itself. They were introduced in Java 1.8 to support the addition of new methods to interfaces without breaking existing code.

Example:
```
public interface MyInterface {

    default void myMethod() {

        System.out.println("MyInterface");

    }

}

public class MyClass implements MyInterface {

    // ...

}
```
Method references:

Method references are a shorthand syntax for writing lambda expressions that call a single method. They provide a way to reuse existing methods as lambda expressions.

Example:
```
List<String> list = Arrays.asList("apple", "banana", "orange", "pear");

list.forEach(System.out::println);
```
Date and Time API:

Java 1.8 introduced a new Date and Time API to replace the old java.util.Date and java.util.Calendar classes. The new API provides a more flexible and concise way to work with dates and times.

Example:
```
LocalDate date = LocalDate.now();

LocalTime time = LocalTime.now();

System.out.println(date);

System.out.println(time);
```
Base64 encoding and decoding:

Java 1.8 introduced a new class called Base64 for encoding and decoding data in Base64 format. It provides a simple way to encode and decode data in Base64 format.

Example:
```
String text = "hello world";

String encoded = Base64.getEncoder().encodeToString(text.getBytes());

String decoded = new String(Base64.getDecoder().decode(encoded));

System.out.println(encoded);

System.out.println(decoded);
```
Type annotations:

Java 1.8 introduced a new feature called type annotations that allow annotations to be applied to any type use. This includes type declarations, type casts, and instanceof expressions.

Example:
```
List<@NonNull String> list = Arrays.asList("apple", "banana", "orange", "pear");
```
CompletableFuture:

CompletableFuture is a new class introduced in Java 1.8 that provides a way to perform asynchronous computations. It allows you to chain multiple asynchronous operations together and handle errors and exceptions.

Example:
```
CompletableFuture.supplyAsync(() -> "hello")

        .thenApplyAsync(s -> s + " world")

        .thenAccept(System.out::println);
```
Parallel Streams:

Parallel Streams are a feature in Java 1.8 that allow for parallel processing of streams. They provide a way to split the stream into multiple parts and process them in parallel for improved performance.

Example:
```
List<String> list = Arrays.asList("apple", "banana", "orange", "pear");

long count = list.parallelStream().filter(e -> e.contains("a")).count();
```
11. JavaFX:

JavaFX is a Java library for building rich client applications. It provides a set of graphics and media APIs that can be used to create GUI applications.

Example:
```
import javafx.application.Application;

import javafx.scene.Scene;

import javafx.scene.control.Label;

import javafx.scene.layout.StackPane;

import javafx.stage.Stage;

public class HelloWorld extends Application {

scss

Copy code

public void start(Stage primaryStage) {

    Label label = new Label("Hello, World!");

    StackPane root = new StackPane();

    root.getChildren().add(label);

    Scene scene = new Scene(root, 300, 250);

    primaryStage.setScene(scene);

    primaryStage.show();

}

public static void main(String[] args) {

    launch(args);

}

}
```
12. Javadoc:

Javadoc is a tool that comes with the JDK for generating documentation from source code comments. It can be used to generate API documentation for classes, interfaces, and methods.

Example:
```
/**

This is a sample class that demonstrates the use of Javadoc comments.

*/

public class SampleClass {

/**

This method adds two integers and returns the result.

@param a the first integer

@param b the second integer

@return the sum of a and b

*/

public int add(int a, int b) {

return a + b;

}

}
```
This cheat sheet provides a quick overview of some of the key features introduced in Java 1.8. While there are many more features and APIs in Java, these are some of the most commonly used ones.
Object Oriented Programming (OOP) Concepts

March 23rd, 2023

Object-oriented programming (OOP) is a programming paradigm that is used to design and build software systems by creating objects that interact with each other. OOP is based on a set of fundamental concepts that help to make code more modular, flexible, and reusable. In this blog, we will cover the key OOP concepts that you need to understand to become a proficient OOP developer.

Class

A class is a blueprint or a template for creating objects. It defines the properties and methods that an object of that class will have. A class can be thought of as a user-defined data type.

Object

An object is an instance of a class. It has its own set of properties and methods, which are defined by the class. Objects are created using the “new” keyword in Java.

Inheritance

Inheritance is a mechanism that allows a class to inherit properties and methods from another class. The class that inherits from another class is called the subclass, and the class that is being inherited from is called the superclass. Inheritance is used to promote code reuse and to create a hierarchy of related classes.

Polymorphism

Polymorphism is the ability of an object to take on different forms. In Java, polymorphism is achieved through method overloading and method overriding. Method overloading allows a class to have multiple methods with the same name but with different parameters. Method overriding allows a subclass to provide its own implementation of a method that is already defined in the superclass.

Encapsulation

Encapsulation is the practice of hiding the internal details of an object from the outside world. This is done by making the data members of the object private and providing public methods to access and modify those data members. Encapsulation helps to improve code maintainability and reduces the likelihood of bugs.

Abstraction

Abstraction is the process of simplifying complex systems by breaking them down into smaller, more manageable parts. In Java, abstraction is achieved through abstract classes and interfaces. An abstract class is a class that cannot be instantiated and is used as a base class for other classes. An interface is a collection of abstract methods that are implemented by classes that implement the interface.

In conclusion, understanding OOP concepts is essential for becoming a proficient software developer. By mastering these fundamental concepts, you will be able to write more modular, flexible, and reusable code. To become proficient in OOP, it is important to practice these concepts through coding exercises and projects. By doing so, you will become more comfortable with these concepts and will be able to apply them to real-world software development projects.
Starting out as a Software Developer

March 22nd, 2023

Programming is a skill that has become increasingly important in today’s world. With the rise of technology, the demand for programmers is at an all-time high. Whether you’re interested in building apps, websites, or even working in data science, learning to code can open up a world of opportunities for you. However, the process of learning to program can be intimidating, especially for beginners. In this blog, we’ll discuss some tips and resources that can help you get started with programming.

Choose a programming language:

Before you start learning to code, you’ll need to choose a programming language. There are many programming languages out there, each with its own strengths and weaknesses. Some popular programming languages include Python, JavaScript, Java, and C++. You’ll want to choose a language that is popular in the field you’re interested in, so do your research and pick a language that will help you reach your goals.

Get familiar with the basics:

Before diving into advanced programming concepts, it’s important to understand the basics of programming. Start with learning about data types, variables, functions, and control structures. Once you have a good grasp of these fundamental concepts, you can move on to more complex topics.

Practice with simple projects:

The best way to learn programming is to start practicing. Start with simple projects that you can complete in a few hours or days. For example, you could build a calculator or a simple game. These projects will help you put your newfound programming knowledge to use and give you a sense of accomplishment.

Join a community:

Joining a community of programmers can be incredibly helpful when you’re starting out. You can find communities on platforms like Reddit, GitHub, and Stack Overflow. These communities can provide you with resources, advice, and even mentorship.

Use online resources:

There are many online resources available to help you learn to program. Websites like Codecademy, Udacity, and Coursera offer free or low-cost programming courses. You can also find tutorials, videos, and articles on programming topics on YouTube and blogs. Additionally, many programming languages have their own documentation, which can be a valuable resource when you’re trying to learn a new language.

Be patient:

Learning to program takes time and patience. It’s important to remember that you won’t become an expert programmer overnight. Keep practicing and don’t get discouraged if you don’t understand a concept right away. With time and practice, you’ll get there.

In conclusion, learning to program can be challenging, but it’s also incredibly rewarding. By following these tips and utilizing the resources available to you, you can start your programming journey with confidence. Good luck!