Question

How do you pass a class type as parameter?

public Configuration getConfig(Object mapper, Object format) {
    Configuration conf = new Configuration(false);
    conf.setClass("mapreduce.map.class", TestMapper.class, Mapper.class);
    conf.setClass("mapreduce.inputformat.class", DatastoreInputFormat.class, InputFormat.class);
    return conf;
}

I want to replace the value TestMapper.class and DatastoreInputFormat.class with the parameters mapper and format, respectively.

I’m not sure how to convert from Object to TestMapper.class.

Answer 1

The parameters to getConfig() should perhaps have Class type in in the first place instead of Object’s. However:

If you want the runtime class of whatever your mapper and format Objects are, just call their .getClass() methods.

 conf.setClass("mapreduce.map.class",mapper.getClass(), Mapper.class);
 conf.setClass("mapreduce.inputformat.class",format.getClass(),InputFormat.class);

So, if your mapper method parameter is actually an instance of TestMapper , mapper.getClass() will return the same object as TestMapper.class does.

If your mapper and parameter already is the .class objects, i.e. you have called the method as foo.getConfig(TestMapper.class,DatastoreInputFormat.class); you can cast your Objects back to a Class object, assuming the conf.setClass() takes Class<?> type:

conf.setClass("mapreduce.map.class",(Class<?>)mapper, Mapper.class);
conf.setClass("mapreduce.inputformat.class",(Class<?>)format,InputFormat.class);