Curso Java. Estructuras principales I. Vídeo 4

Introduction and Overview

In this video, the instructor introduces the Java programming language and discusses the different types of programs that can be created with it.

Types of Programs in Java

• There are three main types of programs that can be created with Java:

• Console applications

• General-purpose applications

• Applets

• Console applications are programs that run in a command window and display their output there. They are typically used for learning purposes and have limited functionality.

• General-purpose applications can be built for various purposes and cover different needs. Examples include Eclipse, a program written in Java, and JDownloader.

• Applets are Java programs that run inside a web browser as plugins. They are often used on web pages to provide interactive content or functionality.

Importance of Starting with Console Applications

• It is recommended to start learning Java by creating console applications because they are easier to program and require less code. Although they may not have visually appealing results, they serve as a good starting point for beginners to learn programming concepts.

Anatomy of a Java Program

• A simple console application is used as an example to understand the anatomy of a Java program.

• Java is case-sensitive, meaning it distinguishes between uppercase and lowercase letters. Care must be taken with syntax when writing code.

• The "public" keyword is an access modifier that determines the visibility of classes, methods, and variables. Its detailed explanation will be covered later in the course.

Conclusion

Understanding Java Programming Basics

In this section, the instructor introduces the concept of programming in Java and explains some fundamental terms and concepts.

Introduction to Java Programming

• The instructor mentions that throughout the course, there will be a lot of code involving a specific instruction that may not be fully understood at first.

• As the course progresses, the instructor assures that concepts will become clearer and more understandable.

• Patience is advised as understanding Java programming requires gradual learning and practice.

Key Concepts in Java Programming

• Every Java program must be within at least one class.

• Code blocks are delimited by keys (opening and closing braces), which define where a class, method, or loop begins and ends.

• It is important to follow the convention of properly opening and closing keys in the correct order for code readability.

• Proper indentation helps distinguish nested code blocks within each other.

Creating Your First Program in Eclipse

• The instructor transitions to creating a program using Eclipse, a popular Java programming editor.

• Opening Eclipse from the corresponding folder is demonstrated.

• Setting up the workspace location for saving code files is explained.

Starting a Java Project in Eclipse

This section explains the steps to start programming in Java using Eclipse. It covers creating a project and specifying its name and location.

Creating a Java Project

• To start programming in Java, the first step is to create a project.

• In Eclipse, go to the File menu and choose "New" > "Java Project".

• In the "Java Project" window, specify a name for the project. Avoid using special characters or spaces.

• By default, Eclipse will save the project in the workspace folder. You can change this location if needed.

• If you want to save it elsewhere, deactivate the "Use default location" option and browse for a different location.

• Click "Finish" to create the project.

Structure of a Java Project in Eclipse

This section explains the structure of a Java project created in Eclipse. It highlights important folders like "bin" and "src".

Structure of a Java Project

• After creating a project, Eclipse creates several subfolders and necessary files within it.

• The important folders within the project are:

• bin: This folder contains compiled bytecode files.

• src: This folder is where you should place your source code files.

• Other directories like metadata are necessary for Eclipse's functioning but can be ignored for now.

Naming Conventions for Projects and Classes

This section discusses naming conventions for projects and classes in Java.

Naming Conventions

• When giving names to projects or classes in Java, it is recommended to follow certain conventions:

• Avoid using special characters or spaces in project names.

• For class names composed of two words, start each word with a capital letter.

• While these conventions are commonly followed, you have the flexibility to deviate from them if desired.

Creating a Class in Eclipse

This section explains how to create a class within a Java project using Eclipse.

Creating a Class

• To create a class in Eclipse, ensure that the project is selected.

• There are multiple ways to create a class:

• From the "File" menu, choose "New" > "Class".

• Use the toolbar button with a small arrow and select "Class".

• Right-click on the src folder, choose "New" > "Class".

• In the "New Java Class" window, specify the destination package and name for the class.

• Click "Finish" to create the class.

Default Folder for Java Programs

In this section, the speaker explains that by default, all Java programs are saved in the "src" folder. However, it is possible to change this location by using packages.

Changing Program Location with Packages

• Java programs are initially saved in the "src" folder.

• To organize programs into subfolders within the "src" folder, packages can be used.

• The option to create a package appears after the "package" keyword.

• The speaker advises giving a name to the class in the "name" field without spaces or special characters.

• Class names should start with an uppercase letter and never with a number.

Creating a Class

This section focuses on creating a class and naming conventions for classes in Java.

Naming Conventions for Classes

• Class names should not contain spaces or special characters.

• Class names should start with an uppercase letter and can include numbers after the first word.

• Eclipse automatically creates classes with public access modifiers and adds opening and closing curly braces.

Package Default Warning

The speaker addresses a warning message related to the default package and explains that it is not necessary to worry about it at this stage.

Default Package Warning

• Eclipse displays a warning message stating that using the default package is discouraged.

• At this point, there is no need to be concerned about this warning as its significance will be explained later.

Writing Code Inside a Class

This section covers how to write code inside a class in Eclipse.

Writing Code Inside a Class

• After creating a class, additional code needs to be written inside it.

• Use the mouse, enter key, or arrow keys to navigate inside the class for writing code.

• The speaker introduces the "public static void main" instruction and explains that its purpose will be clarified later.

Syntax Errors and Green Vertical Line

This section discusses syntax errors in Eclipse and the significance of a green vertical line.

Syntax Errors and Green Vertical Line

• Eclipse detects syntax errors in real-time while coding.

• Unfinished code sections are marked with red underlines or other indicators.

• A green vertical line appears at the exact point where something is missing in the code.

• Pressing the tab key jumps to the location indicated by the green vertical line, allowing quick navigation.

[t=26:08] Completing the Code

In this section, the speaker explains how to complete the code by adding missing elements and fixing warnings.

Opening Curly Brace

• The next step is to open a curly brace after the parentheses.

• Eclipse automatically closes the curly brace when we press Enter, applying indentation.

Structure of the Code

• The code consists of opening and closing curly braces for the class and main method.

• Inside the main method, we write our code.

Printing a Message

• To print a message, we use System.out.println().

• We open parentheses and write our message inside double quotes.

• Pressing Tab moves the cursor to where Eclipse indicates with a green vertical line.

Semicolon Rule in Java

• All statements in Java must end with a semicolon.

• Classes and methods do not require semicolons, but statements within them do.

[t=28:40] Saving Changes and Compiling

This section covers saving changes in Eclipse, generating compiled files, and understanding their purpose.

Saving Changes in Eclipse

• To save changes in Eclipse, press Ctrl + S (Windows) or go to File > Save.

• The asterisk next to the program name indicates unsaved changes.

Generating Compiled Files

• When changes are saved, Eclipse automatically generates a .class file alongside the .java file.

• The generated file contains bytecode that can be executed on any platform.

Multiplatform Execution

• The generated .class file can be executed on different platforms (e.g., Windows, Mac, Linux).

• It is important to match the filename and extension of both .java and .class files.

[t=30:17] Interpreting Compiled Files

This section explains how compiled files are interpreted by JVM and demonstrates how to execute a Java program in Eclipse.

Opening the Console

• To open the console in Eclipse, go to Window > Show View > Console.

• The console displays the output of our Java program.

Executing a Java Program

• To execute a Java program in Eclipse, ensure that the cursor is inside the program (between opening and closing curly braces).

• Click on the play button in the toolbar or press F11.

• The console will display the output of the executed program.

Conclusion