1. Java简介
**1. Introduction to Java**
Java是一种广泛使用的高级编程语言，由Sun Microsystems（现为Oracle Corporation）于1995年发布。Java具有以下特点：
Java is a widely used high-level programming language, released by Sun Microsystems (now Oracle Corporation) in 1995. Java has the following characteristics:
- **跨平台性**：Java程序可以在任何支持Java虚拟机（JVM）的平台上运行。
**Platform Independence**: Java programs can run on any platform that supports the Java Virtual Machine (JVM).
- **面向对象**：Java是一种面向对象的编程语言，支持封装、继承和多态等特性。
**Object-Oriented**: Java is an object-oriented programming language that supports features such as encapsulation, inheritance, and polymorphism.
- **简单易学**：Java的语法相对简单，适合初学者学习。
**Easy to Learn**: Java's syntax is relatively simple, making it suitable for beginners.
---
#### 2. 开发环境搭建
**2. Setting Up the Development Environment**
要开始编写和运行Java程序，你需要安装以下工具：
To start writing and running Java programs, you need to install the following tools:
- **Java Development Kit (JDK)**：JDK包含了编译和运行Java程序所需的工具。
**Java Development Kit (JDK)**: The JDK contains the tools needed to compile and run Java programs.
- **集成开发环境 (IDE)**：推荐使用IntelliJ IDEA、Eclipse或NetBeans等IDE来编写和调试Java代码。
**Integrated Development Environment (IDE)**: It is recommended to use IDEs such as IntelliJ IDEA, Eclipse, or NetBeans to write and debug Java code.
##### 安装步骤：
**Installation Steps:**
1. **下载并安装JDK**：
**Download and Install JDK:**
- 访问[Oracle官网](
https://www.oracle.com/java/technologies/javase-downloads.html)下载适合你操作系统的JDK版本。
Visit the [Oracle website](https://www.oracle.com/java/technologies/javase-downloads.html) to download the JDK version suitable for your operating system.
- 按照安装向导完成安装。
Follow the installation wizard to complete the installation.
2. **设置环境变量**：
**Set Environment Variables:**
- 在Windows系统中，右键点击“此电脑” -> “属性” -> “高级系统设置” -> “环境变量”。
In Windows, right-click on "This PC" -> "Properties" -> "Advanced System Settings" -> "Environment Variables".
- 在“系统变量”中找到`Path`，点击“编辑”，然后添加JDK的`bin`目录路径（例如：`C:\Program Files\Java\jdk-版本号\bin`）。
Find `Path` in "System Variables", click "Edit", and add the JDK's `bin` directory path (e.g., `C:\Program Files\Java\jdk-version\bin`).
- 在macOS或Linux系统中，编辑`~/.bash_profile`或`~/.bashrc`文件，添加以下行：
On macOS or Linux, edit the `~/.bash_profile` or `~/.bashrc` file and add the following lines:
```bash
export JAVA_HOME=
/Library/Java/JavaVirtualMachines/jdk-版本号.jdk/Contents/Home
export PATH=$JAVA_HOME/bin:$PATH
```
- 保存文件并执行`source ~/.bash_profile`或`source ~/.bashrc`使更改生效。
Save the file and execute `source ~/.bash_profile` or `source ~/.bashrc` to apply the changes.
3. **验证安装**：
**Verify Installation:**
- 打开终端或命令提示符，输入`java -version`和`javac -version`，如果显示版本信息，则说明安装成功。
Open the terminal or command prompt, type `java -version` and `javac -version`. If the version information is displayed, the installation is successful.
4. **安装IDE**：
**Install IDE:**
- 下载并安装你选择的IDE（如IntelliJ IDEA）。
Download and install your chosen IDE (e.g., IntelliJ IDEA).
- 启动IDE并创建一个新的Java项目。
Launch the IDE and create a new Java project.
---
#### 3. 第一个Java程序
**3. Your First Java Program**
让我们编写并运行一个简单的Java程序。
Let's write and run a simple Java program.
##### 步骤：
**Steps:**
1. 打开你的IDE，创建一个新的Java项目。
Open your IDE and create a new Java project.
2. 在项目中创建一个新的Java类文件，命名为`HelloWorld.java`。
Create a new Java class file in the project and name it `HelloWorld.java`.
3. 在`HelloWorld.java`文件中输入以下代码：
Enter the following code in the `HelloWorld.java` file:
```java
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
```
4. 保存文件并运行程序。你应该会在控制台看到输出：
Save the file and run the program. You should see the following output in the console:
```
Hello, World!
```
---
#### 4. 代码解释
**4. Code Explanation**
- `public class HelloWorld`：定义了一个名为`HelloWorld`的公共类。类名必须与文件名相同。
`public class HelloWorld`: Defines a public class named `HelloWorld`. The class name must match the file name.
- `public static void main(String[] args)`：这是Java程序的入口点。`main`方法是程序开始执行的地方。
`public static void main(String[] args)`: This is the entry point of a Java program. The `main` method is where the program starts execution.
- `System.out.println("Hello, World!");`：这行代码用于在控制台输出文本。
`System.out.println("Hello, World!");`: This line of code is used to print text to the console.
---
### 作业
**Homework**
1. 确保你已经成功安装JDK并设置好环境变量。
Make sure you have successfully installed the JDK and set up the environment variables.
2. 在你的IDE中创建一个新的Java项目，并编写并运行`HelloWorld`程序。
Create a new Java project in your IDE, write, and run the `HelloWorld` program.
3. 尝试修改`HelloWorld`程序，使其输出不同的文本。
Try modifying the `HelloWorld` program to output different text.
如果你有任何问题或遇到困难，请随时向我提问。下一课我们将深入学习Java的基本语法和数据类型。祝你学习愉快！
If you have any questions or encounter difficulties, feel free to ask me. In the next lesson, we will dive deeper into Java's basic syntax and data types. Happy learning!