Join and CoGroup Operations

/**
 * Join with another DataSet
 * @param other the other DataSet to join with
 * @return JoinOperatorSets for key specification and join configuration
 */
public <R> JoinOperatorSets<T, R> join(DataSet<R> other);

// Inner join on key fields
DataSet<Tuple2<Long, String>> users = env.fromElements(
    new Tuple2<>(1L, "Alice"), new Tuple2<>(2L, "Bob"));
DataSet<Tuple2<Long, String>> orders = env.fromElements(
    new Tuple2<>(1L, "Order1"), new Tuple2<>(1L, "Order2"), new Tuple2<>(2L, "Order3"));

// Join users and orders on user ID
DataSet<Tuple2<Tuple2<Long, String>, Tuple2<Long, String>>> joined = users
    .join(orders)
    .where(0)  // user ID field in users
    .equalTo(0) // user ID field in orders
    .types(Tuple2.class, Tuple2.class);

// Custom join function
DataSet<String> customJoin = users
    .join(orders)
    .where(0)
    .equalTo(0)
    .with(new JoinFunction<Tuple2<Long, String>, Tuple2<Long, String>, String>() {
        @Override
        public String join(Tuple2<Long, String> user, Tuple2<Long, String> order) {
            return user.f1 + " has " + order.f1;
        }
    });

/**
 * Enum defining join types
 */
public enum JoinType {
    INNER,        // Inner join (default)
    LEFT_OUTER,   // Left outer join
    RIGHT_OUTER,  // Right outer join  
    FULL_OUTER    // Full outer join
}

/**
 * Specify the join type
 * @param joinType the type of join to perform
 * @return configured join operator
 */
public JoinOperator<T1, T2, R> with(JoinType joinType);

/**
 * Interface for join functions
 * @param <IN1> type of elements from first DataSet
 * @param <IN2> type of elements from second DataSet  
 * @param <OUT> type of result elements
 */
public interface JoinFunction<IN1, IN2, OUT> extends Function, Serializable {
    /**
     * Join function that combines two elements
     * @param first element from first DataSet
     * @param second element from second DataSet
     * @return combined result element
     */
    OUT join(IN1 first, IN2 second) throws Exception;
}

/**
 * Rich version with access to runtime context
 */
public abstract class RichJoinFunction<IN1, IN2, OUT> 
    extends AbstractRichFunction implements JoinFunction<IN1, IN2, OUT> {
}

/**
 * CoGroup with another DataSet
 * @param other the other DataSet to coGroup with
 * @return CoGroupOperatorSets for key specification and coGroup configuration
 */
public <R> CoGroupOperator.CoGroupOperatorSets<T, R> coGroup(DataSet<R> other);

// CoGroup users and orders
DataSet<String> coGroupResult = users
    .coGroup(orders)
    .where(0)
    .equalTo(0)
    .with(new CoGroupFunction<Tuple2<Long, String>, Tuple2<Long, String>, String>() {
        @Override
        public void coGroup(
            Iterable<Tuple2<Long, String>> users,
            Iterable<Tuple2<Long, String>> orders,
            Collector<String> out) {
            
            Iterator<Tuple2<Long, String>> userIter = users.iterator();
            if (userIter.hasNext()) {
                Tuple2<Long, String> user = userIter.next();
                int orderCount = 0;
                for (Tuple2<Long, String> order : orders) {
                    orderCount++;
                }
                out.collect(user.f1 + " has " + orderCount + " orders");
            }
        }
    });

/**
 * Interface for coGroup functions
 * @param <IN1> type of elements from first DataSet
 * @param <IN2> type of elements from second DataSet
 * @param <OUT> type of result elements
 */
public interface CoGroupFunction<IN1, IN2, OUT> extends Function, Serializable {
    /**
     * CoGroup function that processes groups from both sides
     * @param first iterable of elements from first DataSet
     * @param second iterable of elements from second DataSet
     * @param out collector for result elements
     */
    void coGroup(Iterable<IN1> first, Iterable<IN2> second, Collector<OUT> out) throws Exception;
}

/**
 * Rich version with access to runtime context
 */
public abstract class RichCoGroupFunction<IN1, IN2, OUT>
    extends AbstractRichFunction implements CoGroupFunction<IN1, IN2, OUT> {
}

/**
 * Cross product with another DataSet
 * @param other the other DataSet to cross with
 * @return CrossOperator for cross product configuration
 */
public <R> CrossOperator.DefaultCross<T, R> cross(DataSet<R> other);

// Simple cross product
DataSet<String> colors = env.fromElements("red", "blue");
DataSet<String> sizes = env.fromElements("small", "large");

DataSet<Tuple2<String, String>> crossed = colors
    .cross(sizes)
    .types(String.class, String.class);

// Cross with custom function
DataSet<String> customCross = colors
    .cross(sizes)
    .with(new CrossFunction<String, String, String>() {
        @Override
        public String cross(String color, String size) {
            return size + " " + color + " item";
        }
    });

/**
 * Interface for cross functions
 * @param <IN1> type of elements from first DataSet
 * @param <IN2> type of elements from second DataSet
 * @param <OUT> type of result elements
 */
public interface CrossFunction<IN1, IN2, OUT> extends Function, Serializable {
    /**
     * Cross function that combines elements from both DataSets
     * @param first element from first DataSet
     * @param second element from second DataSet
     * @return combined result element
     */
    OUT cross(IN1 first, IN2 second) throws Exception;
}

/**
 * Rich version with access to runtime context
 */
public abstract class RichCrossFunction<IN1, IN2, OUT>
    extends AbstractRichFunction implements CrossFunction<IN1, IN2, OUT> {
}

/**
 * Union with another DataSet of the same type
 * @param other the other DataSet to union with
 * @return UnionOperator containing elements from both DataSets
 */
public UnionOperator<T> union(DataSet<T> other);

// Union two DataSets
DataSet<String> dataset1 = env.fromElements("a", "b", "c");
DataSet<String> dataset2 = env.fromElements("d", "e", "f");

DataSet<String> combined = dataset1.union(dataset2);
// Result contains: a, b, c, d, e, f

// Union multiple DataSets
DataSet<String> dataset3 = env.fromElements("g", "h");
DataSet<String> allCombined = dataset1.union(dataset2).union(dataset3);

/**
 * Specify key fields by position (for Tuple types)
 * @param fields the field positions to use as keys
 * @return key specification for further configuration
 */
public JoinOperatorSets.JoinOperatorSetsPredicate where(int... fields);

/**
 * Specify key fields by name (for POJO types)
 * @param fields the field names to use as keys
 * @return key specification for further configuration
 */
public JoinOperatorSets.JoinOperatorSetsPredicate where(String... fields);

/**
 * Specify key using key selector function
 * @param keyExtractor function to extract the key
 * @return key specification for further configuration
 */
public <K> JoinOperatorSets.JoinOperatorSetsPredicateWithKeySelector<K> where(KeySelector<T, K> keyExtractor);

/**
 * Specify the matching key fields in the other DataSet
 * @param fields the field positions in the other DataSet
 * @return configured join operator
 */
public JoinOperator.EquiJoin<T1, T2> equalTo(int... fields);

/**
 * Enum for join strategy hints
 */
public enum JoinHint {
    OPTIMIZER_CHOOSES,    // Let optimizer choose strategy
    BROADCAST_HASH_FIRST, // Broadcast first DataSet and use hash join
    BROADCAST_HASH_SECOND,// Broadcast second DataSet and use hash join
    REPARTITION_HASH_FIRST, // Repartition both, use first as build side
    REPARTITION_HASH_SECOND, // Repartition both, use second as build side
    REPARTITION_SORT_MERGE   // Repartition and sort-merge join
}

/**
 * Provide a hint for join execution strategy
 * @param hint the execution strategy hint
 * @return configured join operator
 */
public JoinOperator<T1, T2, R> strategy(JoinHint hint);

import org.apache.flink.api.java.operators.JoinOperator;
import org.apache.flink.api.java.operators.CoGroupOperator;
import org.apache.flink.api.java.operators.CrossOperator;
import org.apache.flink.api.java.operators.UnionOperator;
import org.apache.flink.api.java.operators.join.JoinType;
import org.apache.flink.api.java.operators.join.JoinOperatorSets;
import org.apache.flink.api.common.functions.JoinFunction;
import org.apache.flink.api.common.functions.CoGroupFunction;
import org.apache.flink.api.common.functions.CrossFunction;
import org.apache.flink.api.common.functions.RichJoinFunction;
import org.apache.flink.api.common.functions.RichCoGroupFunction;
import org.apache.flink.api.common.functions.RichCrossFunction;
import org.apache.flink.util.Collector;