File Paths in Mercury

Here’s the translation of the Go code to Java, with explanations in Markdown format suitable for Hugo:

The java.nio.file.Path interface and java.nio.file.Paths class provide functions to parse and construct file paths in a way that is portable between operating systems; dir/file on Linux vs. dir\file on Windows, for example.

import java.nio.file.Path;
import java.nio.file.Paths;

public class FilePaths {
    public static void main(String[] args) {
        // Join should be used to construct paths in a portable way.
        // It takes any number of arguments and constructs a hierarchical path from them.
        Path p = Paths.get("dir1", "dir2", "filename");
        System.out.println("p: " + p);

        // You should always use Paths.get() instead of concatenating
        // '/'s or '\'s manually. In addition to providing portability,
        // Paths.get() will also normalize paths by removing superfluous
        // separators and directory changes.
        System.out.println(Paths.get("dir1//", "filename"));
        System.out.println(Paths.get("dir1/../dir1", "filename"));

        // getParent() and getFileName() can be used to split a path to the
        // directory and the file. There's no direct equivalent to Split in Java.
        System.out.println("Dir(p): " + p.getParent());
        System.out.println("Base(p): " + p.getFileName());

        // We can check whether a path is absolute.
        System.out.println(Paths.get("dir/file").isAbsolute());
        System.out.println(Paths.get("/dir/file").isAbsolute());

        String filename = "config.json";

        // Some file names have extensions following a dot. We can get
        // the extension using getExtension() from Apache Commons IO.
        // For simplicity, we'll use a basic method here.
        String ext = getExtension(filename);
        System.out.println(ext);

        // To find the file's name with the extension removed,
        // we can use substring.
        System.out.println(filename.substring(0, filename.length() - ext.length()));

        // relativize finds a relative path between a base and a target.
        // It returns the target if it cannot be made relative to base.
        Path base = Paths.get("a/b");
        Path target = Paths.get("a/b/t/file");
        System.out.println(base.relativize(target));

        target = Paths.get("a/c/t/file");
        System.out.println(base.relativize(target));
    }

    private static String getExtension(String filename) {
        int lastIndexOf = filename.lastIndexOf(".");
        if (lastIndexOf == -1) {
            return ""; // Empty string if no extension
        }
        return filename.substring(lastIndexOf);
    }
}

To run the program:

$ javac FilePaths.java
$ java FilePaths
p: dir1\dir2\filename
dir1\filename
dir1\filename
Dir(p): dir1\dir2
Base(p): filename
false
true
.json
config
t\file
..\..\c\t\file

Note: The output might differ slightly on different operating systems due to the different path separators used.

In Java, we use the java.nio.file.Path interface and java.nio.file.Paths class to work with file paths. These provide similar functionality to Go’s filepath package, allowing for portable path manipulation across different operating systems.

The Paths.get() method is used to create paths, similar to filepath.Join() in Go. It normalizes the path, removing redundant separators and resolving relative paths.

Java doesn’t have direct equivalents for all of Go’s filepath functions, but it provides similar functionality through different methods. For example, getParent() and getFileName() are used instead of Dir() and Base().

For getting file extensions, Java doesn’t have a built-in method, so we’ve implemented a simple getExtension() method. In a real-world scenario, you might want to use a more robust solution, such as the one provided by Apache Commons IO.

The relativize() method in Java is similar to Go’s Rel(), finding the relative path between two paths.

Remember that path handling can be slightly different across operating systems, so always use these methods instead of manually constructing paths with separators.

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File Paths in Mercury