Prog_1/Tries/Node.java

/**
 * Provides methods to manipulate single Nodes.<br />
 * A Node represents a char in the Trie and provides a children-array
 * that saves following chars. <br />The Node also saves the parent Node.
 * if a character is the last one of a string that is set it contains points.
 * <br /><br />i.e. if "hans" is set with 5 points, <code>points</code>
 * of 's' is 5.
 */
public class Node {

    /**
     * the points of a Student.
     */
    private Integer points;
    /**
     * Node array for children.
     */
    private Node[] children = new Node[26];
    /**
     * Parent Node.
     */
    private Node parent;
    /**
     * The Character of the Node.
     */
    private char ch;

    /**
     * Constructor for root Node.
     */
    public Node() {
        this.points = null;
        this.parent = null;
        this.ch = '+';
    }

    /**
     * Constructor for Node with character <code>ch</code>.
     * @param ch character of the Node
     */
    private Node(char ch) {
        this.points = null;
        this.parent = null;
        this.ch = ch;
    }

    /**
     * Constructor for Node <code>ch</code>s with known parent
     * Node <code>parent</code>.
     * @param ch character of the Node
     * @param parent Parent Node of the Node
     */
    public Node(char ch, Node parent) {   
        Node hlp = new Node(ch);
        hlp.parent = parent;
        parent.setChild(ch, hlp);
    }

    /**
     * Converts a character <code>ch</code> into the index for
     *  the children array.
     * @param ch character to convert
     * @return index for the children array
     */
    private int convertChar(char ch) {
        return ch - 'a';
    }

    /**
     * Sets <code>child</code> with character <code>ch</code>
     *  in children array.
     * @param ch the child's character
     * @param child the child Node
     */
    private void setChild(char ch, Node child) {
        this.children[convertChar(ch)] = child;
    }

    /**
     * Child getter.
     * @param ch character of child to get
     * @return <code>Node</code> of child
     *          or <code>null</code>,  if child does not exist
     */
    public Node getChild(char ch) {
        return this.children[convertChar(ch)];
    }

    /**
     * Searches the subtree for a string <code>key</code>.
     * @param key string to search for
     * @return <code>Node</code> of found key or <code>null</code>
     */
    public Node find(String key) {
        int i = 1;
        Node iterator = this.children[convertChar(key.charAt(0))];
        while (iterator != null && i < key.length()) {
            iterator = iterator.children[convertChar(key.charAt(i))];
            i++;
        }
        if (i == key.length()) {
            return iterator;
        } else {
            return null;
        }
    }

    /**
     * Reset <code>points</code> of Node.
     */
    public void deleteMe() {
        this.points = null;
        cleanup();
    }

    /**
     * Searches for children.
     * @return <code>true</code>, if child was found or<br />
     *          <code>false</code>, if child not available
     */
    private boolean hasChild() {
        for (int i = 0; i < this.children.length; i++) {
            if (this.children[i] != null) {
                return true;
            }
        }
        return false;
    }

    /**
     * Deletes unneeded Nodes after Student deletion.
     */
    private void cleanup() {
        if (hasChild()) {
            return;
            }
        Node iterator = this.parent;
        char isChild = this.ch;
        while (iterator.points == null && iterator.parent != null) {

            //delete edge
            iterator.children[convertChar(isChild)] = null;

            //if another child is set, the Node is still needed
            if (iterator.hasChild()) {
                return;
            }
                isChild = iterator.ch;
                iterator = iterator.parent;
        }

        //delete child Node in root
        iterator.children[convertChar(isChild)] = null;

    }

    /**
     * Method to print a Node and his subtree.<br />
     * Recursive self-calling every child of the Node.
     * @return <code>string</code> of Node and subtree
     */
    public String toString() {
        System.out.print(this.ch);
        if (this.points != null) {
            System.out.print("[" + this.points + "]");
        }
        if (this.hasChild()) {
            System.out.print("(");
            for (int i = 0; i < this.children.length; i++) {
                if (this.children[i] != null) {
                    this.children[i].toString();
                }
            }
            System.out.print(")");
        }
        return "";
    }

    /**
     * Setter for points of Node.
     * @param points to set
     */
    public void setPoints(Integer points) {
        this.points = points;
    }

    /**
     * Getter for Points of Node.
     * @return <code>points</code> of Node
     */
    public Integer getPoints() {
        return this.points;
    }
}