/**
 * This class represents the 8-puzzle problem.
 */
public class PuzzleProblem {
    /**
     * The 8-puzzle problem constructor stores information about the problem,
     * including the current state, the final state for success checking, and
     * an explanatory introduction string.
     * @param initialState the initial state must be installed as the current
     * state of the problem
     */
    public PuzzleProblem(PuzzleState initialState) { ... }

    /**
     * Determines whether the current state of this problem is a success.
     * @return whether the current state is a success
     */
    public boolean success() { ... }

    /**
     * Gets the current state of the problem.
     * @return the current state
     */
    public PuzzleState getCurrentState() { ... }

    /**
     * Sets the current state of the problem.
     * @param currentState the current state
     */
    public void setCurrentState(PuzzleState currentState) { ... }

    /**
     * Get an explanatory introduction string for the problem.
     * @return the introduction string
     */
    public String getIntroduction() { ... }
    ...
}