List file structure within folder or hard drive

This code example lists the files and folders and also the content in all subfolders.
With recursive calls the file/directory tree can be listed with
a relatively small amount of code.
The purpose of the getTabs method and the variable tabCounter is only to
make the output more viewable with indenting for each level.
　
　
import java.io.File;
public class FileStructure {
int tabCounter = 0;
public void listFilesAndFolders(String folder) {
File file = new File(folder);
if (!file.exists() !file.isDirectory()) {
System.out.println("Parameter is not a directory");
System.exit(1);
}
File[] fileArray = file.listFiles();
for (int i = 0; i < fileArray.length; i++) {
if (fileArray[i].isDirectory()) {
System.out.println(getTabs() + "- " + fileArray[i].getName());
tabCounter++;
listFilesAndFolders(fileArray[i].getAbsolutePath());
}
else {
System.out.println(getTabs() + fileArray[i].getName());
}
}
tabCounter--;
}
private String getTabs() {
StringBuffer buffer = new StringBuffer();
for (int i = 0; i < tabCounter; i++)
buffer.append("\t");
return buffer.toString();
}
public static void main(String[] args) {
FileStructure fileStructure = new FileStructure();
fileStructure.listFilesAndFolders("C:\\temp");
}
}