open file txt by notepad++ default java code

You can use Desktop.getDesktop().open(file), but it takes the default system application for opening the specified file.

The advantage to this API is its platform independency.

However, you really need to thoroughly think about what you're going to do if:

Additional info from WVrock

I want to point out that it is possible to use edit() instead of open() to open it with the system's default editing application instead of opening application. Note that an average user doesn't know how to change default editing application and it is usually set to notepad in windows.

Try this:

ProcessBuilder pb = new ProcessBuilder("Notepad++.exe", "myfile.txt");
pb.start();

OR

Runtime runtime = Runtime.getRuntime();
Process process = runtime.exec("C:\\path\\to\\notepad++.exe C:\\path\\to\\file.txt");

For example, if notepad++ is located at C:\Windows\notepad++.exe:

Runtime runtime = Runtime.getRuntime();
Process process = runtime.exec("C:\\Windows\\notepad++.exe C:\\test.txt");

Go to your notepad++ properties and see the path

            try {
                String cmds[] = new String[] { "cmd", "/c","C:\\Program Files (x86)\\Notepad++\\notepad++.exe " , "C:\\Test.txt" };
                Runtime.getRuntime().exec(cmds);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

Right click on that txt file and go properties and change open with to notepad++. Now run your code and you can see now that file open in notepad++.

First case your computer use notepad as default text editor and by doing above steps it will change to notepad++

{ "cmd", "/c","notepad++ C:\Test.txt" };

should work , however in case you do not have notepad++ added in PATH the command will be

{ "cmd", "/c","fullpath-to-notepad++.exe C:\Test.txt" };