DSL to build a tree or "hierarchy" in a visually elegant way --> when you want the hierarchy to be easily readable in the source file

TreeBuilder.java

package rubber.duck;

import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.Lists;
import org.apache.commons.lang.NotImplementedException;

import java.util.List;

// TODO: generate the tree from the list of temporary element holders
// fail fast if an user calls methods in the wrong order
public class TreeBuilder<T> {

    private final List<TemporaryElementHolder<T>> temporaryElementHolders = Lists.newArrayList();


    public TreeBuilder<T> ____(T element) {
        return addElementAtLevel(element, 1);
    }

    public TreeBuilder<T> ________(T element) {
        return addElementAtLevel(element, 2);
    }

    public TreeBuilder<T> ____________(T element) {
        return addElementAtLevel(element, 3);
    }

    public TreeBuilder<T> ________________(T element) {
        return addElementAtLevel(element, 4);
    }

    public TreeBuilder<T> ____________________(T element) {
        return addElementAtLevel(element, 5);
    }

    /**
     * Use this method when your tree is too deep to use the "____" methods.
     */
    public TreeBuilder<T> addElementAtLevel(T element, int level) {
        temporaryElementHolders.add(new TemporaryElementHolder<T>(element, level));
        return this;
    }

    public ImmutableMultimap<T, T> build() {
        throw new NotImplementedException("TODO");
    }

    private static class TemporaryElementHolder<T> {
        final T element;
        final int level;

        private TemporaryElementHolder(T element, int level) {
            this.element = element;
            this.level = level;
        }
    }

}

TreeBuilderDemo.java

package rubber.duck;

import com.google.common.collect.ImmutableMultimap;

public class TreeBuilderDemo {

    public void demo() {

        ImmutableMultimap<String, String> tree = new TreeBuilder<String>()
                .____("a")
                .________("b")
                .____________("c")
                .____________("d")
                .________________("e")
                .____________("f")
                .________("g")
                .____________("h")
                .____("i")
                .build();
    }
}