ColumnInterpreter (Apache HBase

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

直接已知子类:

BigDecimalColumnInterpreter, DoubleColumnInterpreter, LongColumnInterpreter
```
@InterfaceAudience.LimitedPrivate(value="Coprocesssor")
 @InterfaceStability.Evolving
public abstract class ColumnInterpreter<T,S,P extends Message,Q extends Message,R extends 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.

构造器概要

构造器
构造器和说明

ColumnInterpreter()

构造器
构造器和说明
`ColumnInterpreter()`

方法概要

所有方法实例方法抽象方法
限定符和类型	方法和说明
`abstract S`	`add(S l1, S l2)`
`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. returns 0 if they are equal or both are null; > 0 if l1 > l2 or l1 is not null and l2 is 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)`
`abstract S`	`increment(S o)`
`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)`

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 构造器详细资料
  - ColumnInterpreter
```
public ColumnInterpreter()
```
- 方法详细资料
  - getValue
```
public abstract T getValue(byte[] colFamily,
                           byte[] colQualifier,
                           Cell c)
                    throws IOException
```
    参数:
    
    colFamily -
    
    colQualifier -
    
    c -
    
    返回:
    
    value of type T
    
    抛出:
    
    IOException
  - add
```
public abstract S add(S l1,
                      S l2)
```
    参数:
    
    l1 -
    
    l2 -
    
    返回:
    
    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
    
    返回:
    
    max
  - getMinValue
```
public abstract T getMinValue()
```
  - multiply
```
public abstract S multiply(S o1,
                           S o2)
```
    参数:
    
    o1 -
    
    o2 -
    
    返回:
    
    multiplication
  - increment
```
public abstract S increment(S o)
```
    参数:
    
    o -
    
    返回:
    
    increment
  - castToReturnType
```
public abstract S castToReturnType(T o)
```
    provides casting opportunity between the data types.
    
    参数:
    
    o -
    
    返回:
    
    cast
  - 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.
    
    参数:
    
    o -
    
    l -
    
    返回:
    
    Average
  - 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.
    
    返回:
    
    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).
    
    参数:
    
    msg -
  - getProtoForCellType
```
public abstract Q getProtoForCellType(T t)
```
    This method gets the PB message corresponding to the cell type
    
    参数:
    
    t -
    
    返回:
    
    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
    
    参数:
    
    q -
    
    返回:
    
    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
    
    参数:
    
    s -
    
    返回:
    
    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
    
    参数:
    
    r -
    
    返回:
    
    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)
    
    参数:
    
    response -
    
    返回:
    
    cast

类 ColumnInterpreter<T,S,P extends Message,Q extends Message,R extends Message>

构造器概要

方法概要

从类继承的方法 java.lang.Object

构造器详细资料

ColumnInterpreter

方法详细资料

getValue

add

getMaxValue

getMinValue

multiply

increment

castToReturnType

compare

divideForAvg

getRequestData

initialize

getProtoForCellType

getCellValueFromProto

getProtoForPromotedType

getPromotedValueFromProto

castToCellType