利用递归查找目录中的最小和最大文件（包括子目录），代码如下：

package file;

import java.io.File;

public class TestFile5 {

    private static File minFile, maxFile;

    public static void main(String[] args) {
        File root = new File("d:/test");
        findMinAndMax(root);
    }

    public static void findMinAndMax(File rootDirectory) {
        File[] fs = rootDirectory.listFiles();
        for (File f : fs) {
            if (f.isDirectory())
                findMinAndMax(f);
            else {
                if (minFile == null) {
                    minFile = maxFile = f;
                }
                if (f.length() != 0) {
                    if (f.length() < minFile.length())
                        minFile = f;
                    if (f.length() > maxFile.length())
                        maxFile = f;
                }
            }
        }
    }
}