下列代码段编译和运行的结果是：(     )

public static void main(String[] args) {
    String str = "null";
    if (str == null) {
        System.out.println("null");
    } else if(str.length() == 0) {
        System.out.println("zero");
    } else {
        System.out.println("some");
    }
}