如何用记事本运行Java程序？能否运行全类型Java程序及包的使用时机

Hey there! I totally get choosing Notepad for your Java learning journey despite IDEs being available—self-teaching with a basic setup is a great way to grasp the fundamentals deeply. Let's tackle your questions one by one:

1. How to run a Java program using Notepad? #

Follow these straightforward steps (first make sure you have the JDK installed and its bin directory added to your system's PATH):

• Open Notepad and write your Java code. Critical note: If your class is marked public, the filename must exactly match the class name (e.g., a public class HelloWorld needs to be saved as HelloWorld.java).
• Save the file to a folder you can easily reach via the command line (like C:\JavaPractice on Windows or ~/JavaPractice on macOS/Linux).
• Open Command Prompt/Terminal, navigate to your saved folder using the cd command (e.g., cd C:\JavaPractice).
• Compile the code with the Java compiler:

  javac HelloWorld.java
  

  This creates a .class bytecode file in the same folder.
• Run the compiled program:

  java HelloWorld
  

  Don't include the .class extension when running the command!

2. Can you run all types of Java programs (like applets, inheritance-related code) using Notepad? #

Let’s break this down:

• Inheritance-related programs: Absolutely! Inheritance is just a core OOP concept—your code’s structure doesn’t change how you compile or run it. You can write parent/child classes in the same .java file or separate files in Notepad, compile normally, and run the main class exactly like any other program. A simple inheritance setup will work flawlessly with the javac and java commands we covered.
• Applets: Unfortunately, modern Java no longer supports applets. The JDK removed the appletviewer tool after Java 8, and all major browsers have dropped Java applet support entirely. Even if you wrote applet code in Notepad, you wouldn’t be able to run it with current Java versions—applets are effectively obsolete now.

3. When do you need to use package? #

Packages are all about organizing code and avoiding conflicts—here are key scenarios to use them:

• When your codebase grows: Once you have multiple classes that serve related purposes (e.g., a set of input-handling classes, another set for data processing), grouping them into packages keeps your code clean and easy to navigate.
• To avoid class name collisions: If you’re collaborating with others or using external libraries, packages act as unique namespaces. For example, two developers could both have a User class, but putting yours in com.keerthana.learn.users and theirs in com.john.dev.utils prevents conflicts.
• To control access permissions: Java’s access modifiers (like protected or package-private) depend on packages. If you want a method/class to only be accessible to other classes in the same package, using a package is mandatory.
• You can even use packages with Notepad: Add a package statement at the very top of your .java file (e.g., package com.keerthana.learn;). Then create a folder structure matching the package name (e.g., com/keerthana/learn), move your .java file into that folder, compile with javac -d . com/keerthana/learn/YourClass.java, and run with java com.keerthana.learn.YourClass.

内容的提问来源于stack exchange，提问作者Keerthana