OutputStreamWriter 和 FileWriter 有什么区别？

老实说用谷歌搜索。发现这个：OutputStreamWriter vs FileWriter。答案一般谈论 XXXInputStream 和 XXXOutputStream 之间的区别（虽然这很有帮助，但这不是我需要的）。
从第二个链接来看：OutputStream、BufferedWriter 和 FileWriter 的区别。我也没有找到答案。

本质上：
这是完整的类代码：

public class FileWriter extends OutputStreamWriter {
    public FileWriter(String fileName) throws IOException {
        super(new FileOutputStream(fileName));
    }

    public FileWriter(String fileName, boolean append) throws IOException {
        super(new FileOutputStream(fileName, append));
    }

    public FileWriter(File file) throws IOException {
        super(new FileOutputStream(file));
    }

    public FileWriter(File file, boolean append) throws IOException {
        super(new FileOutputStream(file, append));
    }

    public FileWriter(FileDescriptor fd) {
        super(new FileOutputStream(fd));
    }

    public FileWriter(String fileName, Charset charset) throws IOException {
        super(new FileOutputStream(fileName), charset);
    }

    public FileWriter(String fileName, Charset charset, boolean append) throws IOException {
        super(new FileOutputStream(fileName, append), charset);
    }

    public FileWriter(File file, Charset charset) throws IOException {
        super(new FileOutputStream(file), charset);
    }
    public FileWriter(File file, Charset charset, boolean append) throws IOException {
        super(new FileOutputStream(file, append), charset);
    }
}

它绝对实现了所有构造函数OutputStreamWriter。它并没有添加任何新内容。我很困惑。