java _io_面向对象风格递归获得文件夹大小

public  class test {

private  int sum; //文件夹大小
private String path;  //路径
private File f;

public static void main(String[]args) throws IOException
{	
	test t=new test("D:/d");
	System.out.println(t.getSum());
}


public test(String path)
{
	this.path=path;
	this.f=new File(path);
	N(this.f);
}
public int getSum()
{
	return this.sum;
}
//递归打印获得文件夹大小
private int N(File f)
{
	if(null!=f&&f.exists())
	{		
		if(f.isFile()) //是文件才能获得大小
		{
			sum+=f.length();
		}
		else if(f.isDirectory())
		{

			File[] ss=f.listFiles();
			for(File r:ss)
			{
				 N(r);
			}
		}
	}
	return sum;	
}

}