ColumnInterpreter (Apache HBase

java.lang.Object
- org.apache.hadoop.hbase.coprocessor.ColumnInterpreter<T,S,P,Q,R>

Direct Known Subclasses:

BigDecimalColumnInterpreter, DoubleColumnInterpreter, LongColumnInterpreter
```
@InterfaceAudience.LimitedPrivate(value="Coprocesssor")
 @InterfaceStability.Evolving
public abstract class ColumnInterpreter<T,S,P extends com.google.protobuf.Message,Q extends com.google.protobuf.Message,R extends com.google.protobuf.Message>
extends Object
```
Defines how value for specific column is interpreted and provides utility methods like compare, add, multiply etc for them. Takes column family, column qualifier and return the cell value. Its concrete implementation should handle null case gracefully. Refer to LongColumnInterpreter for an example.
Takes two generic parameters and three Message parameters. The cell value type of the interpreter is <T>. During some computations like sum, average, the return type can be different than the cell value data type, for eg, sum of int cell values might overflow in case of a int result, we should use Long for its result. Therefore, this class mandates to use a different (promoted) data type for result of these computations <S>. All computations are performed on the promoted data type <S>. There is a conversion method castToReturnType(Object) which takes a <T> type and returns a <S> type. The AggregateIm>lementation uses PB messages to initialize the user's ColumnInterpreter implementation, and for sending the responses back to AggregationClient.
<T> Cell value data type
<S> Promoted data type
<P> PB message that is used to transport initializer specific bytes
<Q> PB message that is used to transport Cell (<T>) instance
<R> PB message that is used to transport Promoted (<S>) instance

Constructor Summary

Constructors
Constructor and Description

ColumnInterpreter()

Constructors
Constructor and Description
`ColumnInterpreter()`

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`abstract S`	`add(S l1, S l2)` Returns sum or non null value among (if either of them is null); otherwise returns a null.
`abstract T`	`castToCellType(S response)` The response message comes as type S.
`abstract S`	`castToReturnType(T o)` provides casting opportunity between the data types.
`abstract int`	`compare(T l1, T l2)` This takes care if either of arguments are null.
`abstract double`	`divideForAvg(S o, Long l)` used for computing average of <S> data values.
`abstract T`	`getCellValueFromProto(Q q)` This method gets the PB message corresponding to the cell type
`abstract T`	`getMaxValue()` returns the maximum value for this type T
`abstract T`	`getMinValue()`
`abstract S`	`getPromotedValueFromProto(R r)` This method gets the promoted type from the proto message
`abstract Q`	`getProtoForCellType(T t)` This method gets the PB message corresponding to the cell type
`abstract R`	`getProtoForPromotedType(S s)` This method gets the PB message corresponding to the promoted type
`abstract P`	`getRequestData()` This method should return any additional data that is needed on the server side to construct the ColumnInterpreter.
`abstract T`	`getValue(byte[] colFamily, byte[] colQualifier, Cell c)` Returns value of type T
`abstract S`	`increment(S o)` Returns increment
`abstract void`	`initialize(P msg)` This method should initialize any field(s) of the ColumnInterpreter with a parsing of the passed message bytes (used on the server side).
`abstract S`	`multiply(S o1, S o2)` Returns multiplication

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - ColumnInterpreter
```
public ColumnInterpreter()
```
- Method Detail
  - getValue
```
public abstract T getValue(byte[] colFamily,
                           byte[] colQualifier,
                           Cell c)
                    throws IOException
```
    Returns value of type T
    
    Throws:
    
    IOException
  - add
```
public abstract S add(S l1,
                      S l2)
```
    Returns sum or non null value among (if either of them is null); otherwise returns a null.
  - getMaxValue
```
public abstract T getMaxValue()
```
    returns the maximum value for this type T
  - getMinValue
```
public abstract T getMinValue()
```
  - multiply
```
public abstract S multiply(S o1,
                           S o2)
```
    Returns multiplication
  - increment
```
public abstract S increment(S o)
```
    Returns increment
  - castToReturnType
```
public abstract S castToReturnType(T o)
```
    provides casting opportunity between the data types.
  - compare
```
public abstract int compare(T l1,
                            T l2)
```
    This takes care if either of arguments are null. returns 0 if they are equal or both are null;
    - > 0 if l1 > l2 or l1 is not null and l2 is null.
    - < 0 if l1 < l2 or l1 is null and l2 is not null.
  - divideForAvg
```
public abstract double divideForAvg(S o,
                                    Long l)
```
    used for computing average of <S> data values. Not providing the divide method that takes two <S> values as it is not needed as of now.
  - getRequestData
```
public abstract P getRequestData()
```
    This method should return any additional data that is needed on the server side to construct the ColumnInterpreter. The server will pass this to the initialize(P) method. If there is no ColumnInterpreter specific data (for e.g., LongColumnInterpreter) then null should be returned.
    
    Returns:
    
    the PB message
  - initialize
```
public abstract void initialize(P msg)
```
    This method should initialize any field(s) of the ColumnInterpreter with a parsing of the passed message bytes (used on the server side).
  - getProtoForCellType
```
public abstract Q getProtoForCellType(T t)
```
    This method gets the PB message corresponding to the cell type
    
    Returns:
    
    the PB message for the cell-type instance
  - getCellValueFromProto
```
public abstract T getCellValueFromProto(Q q)
```
    This method gets the PB message corresponding to the cell type
    
    Returns:
    
    the cell-type instance from the PB message
  - getProtoForPromotedType
```
public abstract R getProtoForPromotedType(S s)
```
    This method gets the PB message corresponding to the promoted type
    
    Returns:
    
    the PB message for the promoted-type instance
  - getPromotedValueFromProto
```
public abstract S getPromotedValueFromProto(R r)
```
    This method gets the promoted type from the proto message
    
    Returns:
    
    the promoted-type instance from the PB message
  - castToCellType
```
public abstract T castToCellType(S response)
```
    The response message comes as type S. This will convert/cast it to T. In some sense, performs the opposite of castToReturnType(Object)

Class ColumnInterpreter<T,S,P extends com.google.protobuf.Message,Q extends com.google.protobuf.Message,R extends com.google.protobuf.Message>

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

ColumnInterpreter

Method Detail

getValue

add

getMaxValue

getMinValue

multiply

increment

castToReturnType

compare

divideForAvg

getRequestData

initialize

getProtoForCellType

getCellValueFromProto

getProtoForPromotedType

getPromotedValueFromProto

castToCellType