泛型有那么多的好处，为什么Properties没有定义泛型
Properties是HashTable的子类，为什么Properties没有定义泛型呢？他不定义泛型的原因是什么？他的键值都是String类型的，为了什么这样呢？

这种问题看JDK中的 Properties 类 的源代码就OK了：
...............
  public  class Properties extends Hashtable<Object,Object> {
.................
    /**
     * Calls the <tt>Hashtable</tt> method <code>put</code>. Provided for
     * parallelism with the <tt>getProperty</tt> method. Enforces use of
     * strings for property keys and values. The value returned is the
     * result of the <tt>Hashtable</tt> call to <code>put</code>.
     *
     * @param key the key to be placed into this property list.
     * @param value the value corresponding to <tt>key</tt>.
     * @return     the previous value of the specified key in this property
     *             list, or <code>null</code> if it did not have one.
     * @see #getProperty
     * @since    1.2
     */
    public synchronized Object setProperty(String key, String value) {
        return put(key, value);
    }
   ...................
   /**
     * Searches for the property with the specified key in this property list.
     * If the key is not found in this property list, the default property list,
     * and its defaults, recursively, are then checked. The method returns
     * <code>null</code> if the property is not found.
     *
     * @param   key   the property key.
     * @return  the value in this property list with the specified key value.
     * @see     #setProperty
     * @see     #defaults
     */
    public String getProperty(String key) {
        Object oval = super.get(key);
        String sval = (oval instanceof String) ? (String)oval : null;
        return ((sval == null) && (defaults != null)) ? defaults.getProperty(key) : sval;
    }

所以：实际上在向Properties对象中存储数据时调用用了Hashtable类的put(key, value)方法
而从Properties对象中取值时也是调用了Hashtable类的get(key)方法

之所以将Properties类的setProperty()方法的参数强制设置成String类型，要从设计Properties类的初衷说起：
Properties类的使命是读取存储在某些文件中的配置信息或资源

一楼的答得真好{:soso_e179:}