it.fago.experiments.EderChallenge.java

import static it.fago.experiments.EderChallenge.Operation.from;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;

public class EderChallenge {

	public static void main(String[] args) {
		original();
		maybeFunctional();
	}

	private static void original() {
		String table = "table1";
		String previousTable = "tableX";
		Map<String, List<Field<?>>> childrenPerTable = new HashMap<>();
		childrenPerTable.put("table0", new ArrayList<>());

		List<Field<?>> children = childrenPerTable.get(table);

		if (children == null) {
			childrenPerTable.put(previousTable = table, children = new ArrayList<>());
		}
		
		System.out.printf("\n%s\n%s\n%s\n",table,previousTable,children);

	}

	private static void maybeFunctional() {
		
		String table = "table1";
		String previousTable = "tableX";
		Map<String, List<Field<?>>> childrenPerTable = new HashMap<>();
		childrenPerTable.put("table0", new ArrayList<>());

		Operation newChildrenOp = 
				from(table, previousTable, childrenPerTable)
		         .newChildren();
		
		System.out.printf("\n%s\n%s\n%s\n",newChildrenOp.table(),newChildrenOp.previousTable(),newChildrenOp.children());
	}
	

	///////////////////////////////////////////////////////////
	//
	//
	//
	///////////////////////////////////////////////////////////

	public static class Operation {
		private final String table;
		private final String previousTable;
		private final Map<String, List<Field<?>>> childrenTable;

		private Operation(String table, String previousTable, Map<String, List<Field<?>>> childrenTable) {
			this.table = table;
			this.previousTable = previousTable;
			this.childrenTable = childrenTable;
		}

		public final List<Field<?>> children() {
			return this.childrenTable.get(table);
		}

		public final String table() {
			return table;
		}

		public final String previousTable() {
			return previousTable;
		}

		public static final Operation from(Operation operation) {
			Map<String, List<Field<?>>> result = new HashMap<>(operation.childrenTable);
			result.put(operation.table, new ArrayList<>());
			return new Operation(operation.table, operation.table, result);
		}

		public static final Operation from(String table, String previousTable,
				Map<String, List<Field<?>>> childrenTable) {
			return new Operation(table, previousTable, childrenTable);
		}

		public final Operation newChildren() {
			return Optional
					.ofNullable(children())
					   .map(kids -> this)
					.orElseGet(() -> from(this));
		}		
	}// END

}// END