Code:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class CopyFolder {
    File source, dest;

    public CopyFolder ( String sour, String dest) {
        source = new File( sour );
        this.dest = new File( dest );
        if( !(source.isDirectory() && source.exists()) )
          error();
        if( !this.dest.exists() )
          this.dest.mkdir();
        copy();
        }
    
    void copy() {
        copy( source.getPath() );
    }

    void copy( String from ) {
        File dir[] = new File( from + "/." ).listFiles();
        for( int i = 0; i < dir.length; i++ ) {
            if( dir[i].isDirectory() ) {
               new File( dest.getPath() + dir[i].getPath().substring( dest.getPath().length() ) ).mkdir();
               copy( dir[i].getPath() );
            }
            else {
                File fileFrom = new File( dir[i].getPath() );
                File fileTo = new File( dest.getPath() + dir[i].getPath().substring( dest.getPath().length() ) );
                try {
                      FileInputStream in = new FileInputStream( fileFrom );
                   FileOutputStream out = new FileOutputStream( fileTo );
                   byte data[] = new byte[(int)fileFrom.length()];
                   in.read( data );
                   out.write( data, 0, data.length );
                   in.close();
                   out.close();
                }
                catch( FileNotFoundException e ) {
                      e.printStackTrace();
                    System.exit(0);
                }
                catch( IOException e ) {
                      e.printStackTrace();
                    System.exit(0);
                }
            }
        }
    }
    
    void error() {
        System.err.println( "Neregularni parametri!\n" );
        System.exit(0);
    }
    
    public static void main( String[] arg ) {
        new CopyFolder( "/Prvi", "/Drugi" );
    }

}