两者有什么区别

final Configuration conf = getConf();
    conf.set("mapreduce.job.reduce.slowstart.completedmaps", "0.95");

以及

final Configuration conf = new Configuration(); 
    conf.set("mapreduce.job.reduce.slowstart.completedmaps", "0.95");

好像 getConf 始终返回 null 当我手动调用 main ```
MyMain myJob = new MyMain();
myJob.run(new String[]{
"my_input_dir1",
"my_input_dir2"});