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AIMA-Java Core Algorithms from the book Artificial Intelligence a Modern Approach 3rd Ed.

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package aima.core.search.nondeterministic;

import java.util.LinkedList;

import aima.core.agent.Action;

/**
 * Represents a solution plan for an AND-OR search; according to page 135
 * AIMA3e, the plan must be "a subtree that (1) has a goal node at every leaf,
 * (2) specifies one Object at each of its OR nodes, and (3) includes every
 * outcome branch at each of its AND nodes." As demonstrated on page 136, this
 * subtree is implemented as a linked list where every OR node is an Object--
 * satisfying (2)--and every AND node is an if-state-then-plan-else
 * chain--satisfying (3).
 * 
 * @author Andrew Brown
 */
public class Plan extends LinkedList {

	private static final long serialVersionUID = 1L;

	/**
	 * Each step is either an IfStateThenPlan, a Plan, or an Action.
	 */
	LinkedList steps = new LinkedList();

	/**
	 * Empty constructor
	 */
	public Plan() {
	}

	/**
	 * Construct a plan based on a sequence of steps (IfStateThenPlan or a
	 * Plan).
	 * 
	 * @param steps
	 */
	public Plan(Object... steps) {
		for (int i = 0; i < steps.length; i++) {
			add(steps[i]);
		}
	}

	/**
	 * Prepend an action to the plan and return itself.
	 * 
	 * @param action
	 *            the action to be prepended to this plan.
	 * @return this plan with action prepended to it.
	 */
	public Plan prepend(Action action) {
		this.offerFirst(action);
		return this;
	}

	/**
	 * Returns the string representation of this plan
	 * 
	 * @return a string representation of this plan.
	 */
	@Override
	public String toString() {
		StringBuilder s = new StringBuilder();
		s.append("[");
		int count = 0;
		int size = this.size();
		for (Object step : this) {
			s.append(step);
			if (count < size - 1) {
				s.append(", ");
			}
			count++;
		}
		s.append("]");
		return s.toString();
	}
}
 















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