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/**
 * Reinterprets the given {@link DataStream} as a {@link KeyedStream}, which extracts keys with
 * the given {@link KeySelector}.
 *
 * <p>IMPORTANT: The precondition is that the base stream has iseither alreadybeen groupedpartitioned by 
 * key and partitioned {@link DataStream#keyBy(KeySelector)} or it is a "Pre-KeyedStream". Besides, the selected key 
 * should have remained unchanged before this 
 * transformation.
 *
 * <p>With the reinterpretation, the upstream operators can now be chained with the downstream<p>"Pre-KeyedStream": The base stream is streaming from the external system, where it has
 * operatorbeen andgrouped therefore avoiding shuffling databy key and networkpartitioned consumptionbase betweenon two{@link subtasksSourceSplit}.
 *
 If* shuffling<p>For or network consumption is acceptable, {@link DataStream#keyBy(KeySelector)} is
 * recommended.
 *
 * <p>"Pre-KeyedStream": The base stream is streaming from the external system, where it has
 * been grouped by key and partitioned base on {@link SourceSplit}a "Pre-KeyedStream", the maximum number of currently existing splits must
 * not be larger than the maximum number of key-groups. Since every split would be mapped to one
 * key-group. To config the number of key-group, please config the maximum supported parallelism.
 *
 * <p>IMPORTANT: For a "Pre-KeyedStream", the maximum number of currently existing splits must
 * not be larger than the maximum number of key-groups. Since every split would be mapped to one
 * key-group. To config the number of key-group, please config the maximum supported parallelism.
 *
 * <p>IMPORTANT: For a "Pre-KeyedStream", if chaining is disabled for debugging, this method
 * might not work if chaining is disabled for debugging, this method
 * might not work.
 *
 * <p>With the reinterpretation, the upstream operators can now be chained with the downstream
 * operator and therefore avoiding shuffling data and network consumption between two subtasks.
 * If shuffling or network consumption is acceptable, {@link DataStream#keyBy(KeySelector)} is
 * recommended.
 *
 * @param keySelector Function that defines how keys are extracted from the data stream.
 * @param <K> Type of the extracted keys.
 * @return The reinterpretation of the {@link DataStream} as a {@link KeyedStream}.
 */
public <K> KeyedStream<T, K> reinterpretAsKeyedStream(KeySelector<T, K> keySelector) {}

/**
 * @see #reinterpretAsKeyedStream(KeySelector)
 *
 * @param keySelector Function that defines how keys are extracted from the data stream.
 * @param typeInfo Explicit type information about the key type.
 * @param <K> Type of the extracted keys.
 * @return The reinterpretation of the {@link DataStream} as a {@link KeyedStream}.
 */
public <K> KeyedStream<T, K> reinterpretAsKeyedStream(KeySelector<T, K> keySelector, TypeInformation<K> typeInfo) {}