org.eclipse.rdf4j.federated.evaluation.join

## Class HashJoin

- java.lang.Object
- - org.eclipse.rdf4j.common.iteration.AbstractCloseableIteration<E,X>
  - - org.eclipse.rdf4j.common.iteration.LookAheadIteration<T,QueryEvaluationException>
    - - org.eclipse.rdf4j.federated.evaluation.concurrent.ParallelExecutorBase<T>
      - - org.eclipse.rdf4j.federated.evaluation.join.JoinExecutorBase<BindingSet>
        - - org.eclipse.rdf4j.federated.evaluation.join.HashJoin

- All Implemented Interfaces:
    AutoCloseable, Runnable, CloseableIteration<BindingSet,QueryEvaluationException>, Iteration<BindingSet,QueryEvaluationException>, ParallelExecutor<BindingSet>

      public class HashJoin
      extends JoinExecutorBase<BindingSet>

  Operator for a hash join of tuple expressions.
  Since:
    6.0
  Author:
    Andreas Schwarte

- - ### Field Summary

    - ### Fields inherited from class org.eclipse.rdf4j.federated.evaluation.join.JoinExecutorBase

      `bindings, joinVars, leftIter, rightArg`

    - ### Fields inherited from class org.eclipse.rdf4j.federated.evaluation.concurrent.ParallelExecutorBase

      `evaluationThread, executorId, finished, log, NEXT_EXECUTOR_ID, queryInfo, rightIter, rightQueue, strategy`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `HashJoin(FederationEvalStrategy strategy, CloseableIteration<BindingSet,QueryEvaluationException> leftIter, TupleExpr rightArg, Set<String> joinVars, BindingSet bindings, QueryInfo queryInfo)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `handleBindings()` Implementations must implement this method to handle bindings.
    `protected void` | `performJoin(Collection<BindingSet> leftBlock, Collection<BindingSet> rightBlock, Set<String> joinVariables, Collection<String> freeVariablesRight)` Perform the join and add the result to this cursor.

    - ### Methods inherited from class org.eclipse.rdf4j.federated.evaluation.join.JoinExecutorBase

      `getExecutorType, getJoinVars, handleClose, performExecution, setJoinVars`

    - ### Methods inherited from class org.eclipse.rdf4j.federated.evaluation.concurrent.ParallelExecutorBase

      `addResult, checkTimeout, done, getDisplayId, getId, getNextElement, getQueryInfo, isFinished, run, toss, toString`

    - ### Methods inherited from class org.eclipse.rdf4j.common.iteration.LookAheadIteration

      `hasNext, next, remove`

    - ### Methods inherited from class org.eclipse.rdf4j.common.iteration.AbstractCloseableIteration

      `close, isClosed`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface org.eclipse.rdf4j.common.iteration.Iteration

      `stream`

- - ### Constructor Detail

    - #### HashJoin

          public HashJoin(FederationEvalStrategy strategy,
                          CloseableIteration<BindingSet,QueryEvaluationException> leftIter,
                          TupleExpr rightArg,
                          Set<String> joinVars,
                          BindingSet bindings,
                          QueryInfo queryInfo)
                   throws QueryEvaluationException

      Throws:
        `QueryEvaluationException`

  - ### Method Detail

    - #### handleBindings

          protected void handleBindings()
                                 throws Exception

      Description copied from class: `JoinExecutorBase`
      Implementations must implement this method to handle bindings. Use the following as a template `while (!closed && leftIter.hasNext()) { // your code }` and add results to rightQueue. Note that addResult() is implemented synchronized and thus thread safe. In case you can guarantee sequential access, it is also possible to directly access rightQueue Note that the implementation must block until the entire join is executed.
      Specified by:
        `handleBindings` in class `JoinExecutorBase<BindingSet>`
      Throws:
        `Exception`

    - #### performJoin

          protected void performJoin(Collection<BindingSet> leftBlock,
                                     Collection<BindingSet> rightBlock,
                                     Set<String> joinVariables,
                                     Collection<String> freeVariablesRight)

      Perform the join and add the result to this cursor.

      See `join(Collection, Collection, Set, Collection)` and `ParallelExecutorBase.addResult(CloseableIteration)`.

      Parameters:
        `leftBlock` -
        `rightBlock` -
        `joinVariables` -
        `freeVariablesRight` -

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