function HashTable() {
    var size = 0;
    var entry = new Object();

    this.add = function (key, value) {
        if (!this.containsKey(key)) {
            size++;
        }
        entry[key] = value;
    }

    this.getValue = function (key) {
        return this.containsKey(key) ? entry[key] : null;
    }

    this.remove = function (key) {
        if (this.containsKey(key) && (delete entry[key])) {
            size--;
        }
    }

    this.containsKey = function (key) {
        return (key in entry);
    }

    this.containsValue = function (value) {
        for (var prop in entry) {
            if (entry[prop] == value) {
                return true;
            }
        }
        return false;
    }

    this.getValues = function () {
        var values = new Array();
        for (var prop in entry) {
            values.push(entry[prop]);
        }
        return values;
    }

    this.getKeys = function () {
        var keys = new Array();
        for (var prop in entry) {
            keys.push(prop);
        }
        return keys;
    }

    this.getSize = function () {
        return size;
    }

    this.clear = function () {
        size = 0;
        entry = new Object();
    }
}