What is ObjectInspector functionality ?

      Hive uses ObjectInspector to analyze the internal structure of the row object and also the structure of the individual columns. 

     ObjectInspector provides a uniform way to access complex objects that can be stored in multiple formats in the memory, including: 

1. Instance of a Java class (Thrift or native Java) 
2. A standard Java object (we use java.util.List to represent Struct and Array, and use java.util.Map to represent Map) 
3. A lazily-initialized object (For example, a Struct of string fields stored in a single Java string object with starting offset for each field) 

     A complex object can be represented by a pair of ObjectInspector and Java Object. The ObjectInspector not only tells us the structure of the Object, but also gives us ways to access the internal fields inside the Object.