GroupedCursor (Carbonado 1.2.3 API)

java.lang.Object
+
- com.amazon.carbonado.cursor.AbstractCursor<G>
- +
  - com.amazon.carbonado.cursor.GroupedCursor<S,G>
  +
+

+
Type Parameters:
S - source type, can be anything
G - aggregate type, can be anything
+
+
All Implemented Interfaces:
+
Cursor<G>
+
+
+
+
```
public abstract class GroupedCursor<S,G>
+extends AbstractCursor<G>
```
+
Abstract cursor for aggregation and finding distinct data. The source cursor + must be ordered in some fashion by the grouping properties. The arrangement of + properties must match, but it does not matter if they are ascending or + descending.
+
Author:
+
Brian S O'Neill
+
See Also:
SortedCursor
+

+ +

Constructor Summary

+ + + + + + + + + + + + + + +

Constructors
Modifier	Constructor and Description
`protected`	`GroupedCursor(Cursor<S> cursor, + java.lang.Class<S> type, + java.lang.String... groupProperties)` + Create a GroupedCursor using properties to define the group + comparator. +
`protected`	`GroupedCursor(Cursor<S> cursor, + java.util.Comparator<S> groupComparator)` + Create a GroupedCursor with an existing group comparator. +

+ +

+ + +

Method Summary

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Methods
Modifier and Type	Method and Description
`protected abstract void`	`addToGroup(S groupMember)` + This method is called when more entries are found for the current + group. +
`protected abstract void`	`beginGroup(S groupLeader)` + This method is called for the first entry in a group. +
`void`	`close()` + Call close to release any resources being held by this cursor. +
`java.util.Comparator<S>`	`comparator()` + Returns the comparator used to identify group boundaries. +
`protected abstract G`	`finishGroup()` + This method is called when a group is finished, and it can return an + aggregate. +
`boolean`	`hasNext()` + Returns true if this cursor has more elements. +
`G`	`next()` + Returns the next element from this cursor. +
`int`	`skipNext(int amount)` + Skips forward by the specified amount of elements, returning the actual + amount skipped. +

+ + +
Methods inherited from class com.amazon.carbonado.cursor.AbstractCursor
+copyInto, copyInto, toList, toList

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

+ +
- + + +
  Constructor Detail
  + + + +
  - +
    GroupedCursor
    +
```
protected GroupedCursor(Cursor<S> cursor,
+             java.util.Comparator<S> groupComparator)
```
    +
    Create a GroupedCursor with an existing group comparator. The comparator + defines the ordering of the source cursor, and it should be a partial + odering. If group comparator defines a total ordering, then all groups + have one member.
    +
    Parameters:
    cursor - source of elements which must be ordered properly
    groupComparator - comparator which defines ordering of source cursor
    +
  + + + +
  - +
    GroupedCursor
    +
```
protected GroupedCursor(Cursor<S> cursor,
+             java.lang.Class<S> type,
+             java.lang.String... groupProperties)
```
    +
    Create a GroupedCursor using properties to define the group + comparator. The set of properties defines the ordering of the source + cursor, and it should be a partial ordering. If properties define a + total ordering, then all groups have one member.
    +
    Parameters:
    cursor - source of elements which must be ordered properly
    type - type of storable to create cursor for
    groupProperties - list of properties to group by
    +
    Throws:
    +
    java.lang.IllegalArgumentException - if any property is null or not a member + of storable type
    +
  +
+ +
- + + +
  Method Detail
  + + + +
  - +
    comparator
    +
```
public java.util.Comparator<S> comparator()
```
    +
    Returns the comparator used to identify group boundaries.
    +
  + + + + + +
  - +
    beginGroup
    +
```
protected abstract void beginGroup(S groupLeader)
+                            throws FetchException
```
    +
    This method is called for the first entry in a group. This method is not + called again until after finishGroup is called.
    +
    Parameters:
    groupLeader - first entry in group
    +
    Throws:
    +
    FetchException
    +
  + + + + + +
  - +
    addToGroup
    +
```
protected abstract void addToGroup(S groupMember)
+                            throws FetchException
```
    +
    This method is called when more entries are found for the current + group. This method is not called until after beginGroup has been + called. It may called multiple times until finishGroup is called.
    +
    Parameters:
    groupMember - additional entry in group
    +
    Throws:
    +
    FetchException
    +
  + + + +
  - +
    finishGroup
    +
```
protected abstract G finishGroup()
+                          throws FetchException
```
    +
    This method is called when a group is finished, and it can return an + aggregate. Simply return null if aggregate should be filtered out.
    +
    Returns:
    aggregate, or null to filter it out
    +
    Throws:
    +
    FetchException
    +
  + + + +
  - +
    close
    +
```
public void close()
+           throws FetchException
```
    +
    Description copied from interface: Cursor
    +
    Call close to release any resources being held by this cursor. Further + operations on this cursor will behave as if there are no results.
    +
    Throws:
    +
    FetchException
    +
  + + + +
  - +
    hasNext
    +
```
public boolean hasNext()
+                throws FetchException
```
    +
    Description copied from interface: Cursor
    +
    Returns true if this cursor has more elements. In other words, returns + true if next would return an element rather than throwing + an exception.
    +
    Throws:
    +
    FetchException - if storage layer throws an exception
    +
  + + + +
  - +
    next
    +
```
public G next()
+       throws FetchException
```
    +
    Description copied from interface: Cursor
    +
    Returns the next element from this cursor. This method may be called + repeatedly to iterate through the results.
    +
    Throws:
    +
    FetchException - if storage layer throws an exception
    +
  + + + +
  - +
    skipNext
    +
```
public int skipNext(int amount)
+             throws FetchException
```
    +
    Description copied from interface: Cursor
    +
    Skips forward by the specified amount of elements, returning the actual + amount skipped. The actual amount is less than the requested amount only + if the end of the results was reached.
    +
    +
    Specified by:
    +
    skipNext in interface Cursor<G>
    +
    Overrides:
    +
    skipNext in class AbstractCursor<G>
    +
    Parameters:
    amount - maximum amount of elements to skip
    +
    Returns:
    actual amount skipped
    +
    Throws:
    +
    FetchException - if storage layer throws an exception
    +
  +
+

Class GroupedCursor<S,G>

Constructor Summary

Method Summary

Methods inherited from class com.amazon.carbonado.cursor.AbstractCursor

Methods inherited from class java.lang.Object

Constructor Detail

GroupedCursor

GroupedCursor

Method Detail

comparator

beginGroup

addToGroup

finishGroup

close

hasNext

next

skipNext