java源碼中的不變模式

public static class SimpleImmutableEntry
        implements Map.Entry, Serializable
    {

        public Object getKey()
        {
            return key;
        }

        public Object getValue()
        {
            return value;
        }
  /**
     * 簡單的說就是不支持set操作

     */

        public Object setValue(Object obj)

        {
            throw new UnsupportedOperationException();
        }

        public boolean equals(Object obj)
        {
            if(!(obj instanceof Map.Entry))
            {
                return false;
            } else
            {
                Map.Entry entry = (Map.Entry)obj;
                return AbstractMap.eq(key, entry.getKey()) && AbstractMap.eq(value, entry.getValue());
            }
        }

        public int hashCode()
        {
            return (key != null ? key.hashCode() : 0) ^ (value != null ? value.hashCode() : 0);
        }

        public String toString()
        {
            return (new StringBuilder()).append(key).append("=").append(value).toString();
        }

        private static final long serialVersionUID = 7138329143949025153L;
        private final Object key;
        private final Object value;

        public SimpleImmutableEntry(Object obj, Object obj1)
        {
            key = obj;
            value = obj1;
        }

        public SimpleImmutableEntry(Map.Entry entry)
        {
            key = entry.getKey();
            value = entry.getValue();
        }
    }