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  1. ,
    via javacodegeeks.com by Unknown author

    Causes : The Collection is internally modified, while a thread is iterating over it. OR after the creation of an iterator, the Collection is internally modified by any method other than the iterator’s own methods for removal and addition.

  2. ,
    via oracle.com by Unknown author

    In order to avoid more than one threads accessing or modifying the same object, you can synchronize them over the object, in order to allow only one thread to manipulate it over time.

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java.util.ConcurrentModificationException: null	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:886)	at java.util.ArrayList$Itr.next(ArrayList.java:836)	at org.openrdf.model.impl.TreeModel.choose(TreeModel.java:474)	at org.openrdf.model.impl.TreeModel.matchPattern(TreeModel.java:406)	at org.openrdf.model.impl.TreeModel.contains(TreeModel.java:250)	at org.openrdf.sail.nativerdf.MemoryOverflowModel.contains(MemoryOverflowModel.java:127)	at org.openrdf.model.impl.FilteredModel.contains(FilteredModel.java:157)	at org.openrdf.model.impl.AbstractModel.isEmpty(AbstractModel.java:58)	at org.openrdf.sail.base.SailDatasetImpl.difference(SailDatasetImpl.java:286)	at org.openrdf.sail.base.SailDatasetImpl.getStatements(SailDatasetImpl.java:265)	at org.openrdf.sail.base.DelegatingSailDataset.getStatements(DelegatingSailDataset.java:79)	at org.openrdf.sail.base.DelegatingSailDataset.getStatements(DelegatingSailDataset.java:79)	at org.openrdf.sail.base.UnionSailDataset.getStatements(UnionSailDataset.java:111)	at org.openrdf.sail.base.SailSourceConnection.getStatementsInternal(SailSourceConnection.java:258)	at org.openrdf.sail.helpers.SailConnectionBase.getStatements(SailConnectionBase.java:328)	at org.openrdf.sail.lucene.LuceneTripleSource.getStatements(LuceneTripleSource.java:284)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:517)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:226)	at org.openrdf.query.algebra.evaluation.iterator.JoinIterator.(JoinIterator.java:54)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:861)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:824)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:232)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.(LeftJoinIterator.java:65)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:883)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:827)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:232)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.(LeftJoinIterator.java:65)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:883)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:827)	at org.openrdf.query.algebra.evaluation.impl.EvaluationStrategyImpl.evaluate(EvaluationStrategyImpl.java:232)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:88)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:33)	at info.aduna.iteration.LookAheadIteration.lookAhead(LookAheadIteration.java:91)	at info.aduna.iteration.LookAheadIteration.hasNext(LookAheadIteration.java:60)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:80)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:33)	at info.aduna.iteration.LookAheadIteration.lookAhead(LookAheadIteration.java:91)	at info.aduna.iteration.LookAheadIteration.hasNext(LookAheadIteration.java:60)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:80)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:33)	at info.aduna.iteration.LookAheadIteration.lookAhead(LookAheadIteration.java:91)	at info.aduna.iteration.LookAheadIteration.hasNext(LookAheadIteration.java:60)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:80)	at org.openrdf.query.algebra.evaluation.iterator.LeftJoinIterator.getNextElement(LeftJoinIterator.java:33)	at info.aduna.iteration.LookAheadIteration.lookAhead(LookAheadIteration.java:91)	at info.aduna.iteration.LookAheadIteration.hasNext(LookAheadIteration.java:60)	at info.aduna.iteration.ConvertingIteration.hasNext(ConvertingIteration.java:73)	at info.aduna.iteration.ConvertingIteration.hasNext(ConvertingIteration.java:73)	at info.aduna.iteration.IterationWrapper.hasNext(IterationWrapper.java:68)	at info.aduna.iteration.FilterIteration.findNextElement(FilterIteration.java:79)	at info.aduna.iteration.FilterIteration.hasNext(FilterIteration.java:54)	at info.aduna.iteration.IterationWrapper.hasNext(IterationWrapper.java:68)	at info.aduna.iteration.LimitIteration.hasNext(LimitIteration.java:73)	at info.aduna.iteration.IterationWrapper.hasNext(IterationWrapper.java:68)	at info.aduna.iteration.IterationWrapper.hasNext(IterationWrapper.java:68)	at org.openrdf.query.QueryResults.report(QueryResults.java:155)	at org.openrdf.http.server.repository.TupleQueryResultView.renderInternal(TupleQueryResultView.java:110)	at org.openrdf.http.server.repository.QueryResultView.render(QueryResultView.java:84)	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1228)	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1011)	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:955)	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868)	at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)	at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)	at com.github.ziplet.filter.compression.CompressingFilter.doFilter(CompressingFilter.java:300)	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)	at java.lang.Thread.run(Thread.java:745)