【编程语言】避免创建不必要的对象

编程时重用最好能重用对象，而不是每次需要的时候都去创建一个同样功能的新对象，如果对象是不可变的，则它可以始终被重用

除了重用那些不可变的对象外，也可以重用那些已知的不会被修改的可变对象，下面举一个常见的例子说明减少创建对象对代码优化

的重要性

模型说明：

其中涉及了可变的Date对象，它的值一旦计算出来就不在改变，下面建立一个模型：其中一个人，并有IsPost90s方法，判断此人是否为90后

模型代码：

代码片段一：



1.  <span >/**</span>
2.  <span > * 需求：判断此人是否属于属于90后，即出生年在1990年至1999年之间</span>
3.  <span > * @author RUJIA_LI</span>
4.  <span > *</span>
5.  <span > */</span>
6.  <span >public</span><span > </span><span >class</span><span > </span><span >Person1</span><span > </span><span >{</span>
7.  <span >    </span><span >private</span><span >   </span><span >String</span><span > name</span><span >;</span>
8.  <span >    </span><span >private</span><span >   </span><span >Date</span><span > birthDate</span><span >;</span>
9.  <span >    </span><span >public</span><span > </span><span >Person1</span><span > </span><span >(</span><span >String</span><span > name</span><span >,</span><span > </span><span >Date</span><span > birthDate </span><span >)</span><span > </span><span >{</span>
10.  <span >        </span><span >this</span><span >.</span><span >name      </span><span >=</span><span > name</span><span >;</span>
11.  <span >        </span><span >this</span><span >.</span><span >birthDate </span><span >=</span><span > birthDate</span><span >;</span>
12.  <span >    </span><span >}</span>
13.  <span >    </span><span >public</span><span > </span><span >boolean</span><span > </span><span >IsPost90s</span><span >(){</span>
14.  <span >        </span><span >Calendar</span><span > cal </span><span >=</span><span >  </span><span >Calendar</span><span >.</span><span >getInstance</span><span >(</span><span >TimeZone</span><span >.</span><span >getTimeZone</span><span >(</span><span >"GMT"</span><span >));</span>
15.  <span >        cal</span><span >.</span><span >set</span><span >(</span><span >1990</span><span >,</span><span > </span><span >Calendar</span><span >.</span><span >JANUARY</span><span >,</span><span > </span><span >1</span><span >,</span><span > </span><span >0</span><span >,</span><span > </span><span >0</span><span >,</span><span > </span><span >0</span><span >);</span>
16.  <span >        </span><span >Date</span><span >  startdate </span><span >=</span><span > cal</span><span >.</span><span >getTime</span><span >();</span>
17.  <span >        cal</span><span >.</span><span >set</span><span >(</span><span >1999</span><span >,</span><span > </span><span >Calendar</span><span >.</span><span >JANUARY</span><span >,</span><span > </span><span >1</span><span >,</span><span > </span><span >0</span><span >,</span><span > </span><span >0</span><span >,</span><span > </span><span >0</span><span >);</span>
18.  <span >        </span><span >Date</span><span >  enddate </span><span >=</span><span > cal</span><span >.</span><span >getTime</span><span >();</span>
19.  <span >        </span><span >return</span><span > birthDate</span><span >.</span><span >compareTo</span><span >(</span><span >startdate</span><span >)&gt;=</span><span >0</span><span >&amp;&amp;</span><span >birthDate</span><span >.</span><span >compareTo</span><span >(</span><span >enddate</span><span >)&lt;</span><span >0</span><span >;</span>
20.  <span >    </span><span >}</span>    
21.  <span >}</span>