public class FileExtension {

 /**
 * delete a specify file
 * @param filename : specify a file
 */   

public static void DeleteFile(String filename){} //这个函数的功能是删除一个指定的存在的文件

 protected static void fail(String msg) throws IllegalArgumentException{
 throw new IllegalArgumentException(msg);
 }

} 

public static void DeleteFile(String filename){
 File file = new File(filename);
 
 if(!file.exists())
  fail("Delete: no such file or directory:" + filename);
 if(!file.canWrite())
  fail("Delete: write protected: " + filename);
 
 if(file.isDirectory()){
  String[] files = file.list();
  if(files.length > 0)
  fail("Delete: directory not empty: " + filename);
 }
 
 boolean success = file.delete();
 
 if(!success)
  fail("Delete: deletion failed");
 }