java将文件压缩为Zip文件问题

private void zip(ZipOutputStream out, File f, String base) throws Exception {
if (f.isDirectory()) {
File[] fl = f.listFiles();
out.putNextEntry(new ZipEntry(base + "/"));
base = base.length() == 0 ? "" : base + "/";
for (int i = 0; i < fl.length; i++) {
zip(out, fl[i], base + fl[i].getName());
}
}
else {
out.putNextEntry(new ZipEntry(base));
FileInputStream in = new FileInputStream(f);
int b;
System.out.println(base);
while ( (b = in.read()) != -1) {
out.write(b);
}
in.close();
}

这段代码看了几遍，始终难以理解它的意思，谁能详细解释一下，base在这里是什么意思？ base = base.length() == 0 ? "" : base + "/";这句是干什么的？还有ZipEntry类是创建文件进入点， out.putNextEntry(new ZipEntry(base + "/"));究竟执行了什么操作？