When should I use File.separator and when File.pathSeparator?

If you mean File.separator and File.pathSeparator then:

File.pathSeparator is used to separate individual file paths in a list of file paths. Consider on windows, the PATH environment variable. You use a ; to separate the file paths so on Windows File.pathSeparator would be ;.

File.separator is either / or \ that is used to split up the path to a specific file. For example on Windows it is \ or C:\Documents\Test

---

java.io.File class contains four static separator variables. For better understanding, Let's understand with the help of some code

separator: Platform dependent default name-separator character as String. For windows, it’s ‘\’ and for unix it’s ‘/’ separatorChar: Same as separator but it’s char pathSeparator: Platform dependent variable for path-separator. For example PATH or CLASSPATH variable list of paths separated by ‘:’ in Unix systems and ‘;’ in Windows system pathSeparatorChar: Same as pathSeparator but it’s char

Note that all of these are final variables and system dependent.

Here is the java program to print these separator variables. FileSeparator.java

import java.io.File;

public class FileSeparator {

    public static void main(String[] args) {
        System.out.println("File.separator = "+File.separator);
        System.out.println("File.separatorChar = "+File.separatorChar);
        System.out.println("File.pathSeparator = "+File.pathSeparator);
        System.out.println("File.pathSeparatorChar = "+File.pathSeparatorChar);
    }

}

Output of above program on Unix system:

File.separator = /
File.separatorChar = /
File.pathSeparator = :
File.pathSeparatorChar = :

Output of the program on Windows system:

File.separator = \
File.separatorChar = \
File.pathSeparator = ;
File.pathSeparatorChar = ;

To make our program platform independent, we should always use these separators to create file path or read any system variables like PATH, CLASSPATH.

Here is the code snippet showing how to use separators correctly.

//no platform independence, good for Unix systems
File fileUnsafe = new File("tmp/abc.txt");
//platform independent and safe to use across Unix and Windows
File fileSafe = new File("tmp"+File.separator+"abc.txt");

---

You use separator when you are building a file path. So in unix the separator is /. So if you wanted to build the unix path /var/temp you would do it like this:

String path = File.separator + "var"+ File.separator + "temp"

You use the pathSeparator when you are dealing with a list of files like in a classpath. For example, if your app took a list of jars as argument the standard way to format that list on unix is: /path/to/jar1.jar:/path/to/jar2.jar:/path/to/jar3.jar

So given a list of files you would do something like this:

String listOfFiles = ...
String[] filePaths = listOfFiles.split(File.pathSeparator);

---