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<h1 class="title-article">JDK8新特性：函数式接口@FunctionalInterface的使用说明</h1>
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<span class="article-type type-1 float-left">原创</span> <a class="follow-nickName" href="https://me.csdn.net/aitangyong" target="_blank" rel="noopener">aitangyong</a>
<span class="time">最后发布于2017-01-06 14:03:29 </span>
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<div class="up-time">发布于2017-01-06 14:03:29</div>
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<p><span style="font-size:18px;">我们常用的一些接口Callable、Runnable、Comparator等在JDK8中都添加了<span style="font-size:18px;">@FunctionalInterface注解。</span></span></p>
<p><span style="font-size:18px;"><span style="font-size:18px;"><img src="https://www.icode9.com/i/?i=20170106133721767" alt=""><br></span></span></p>
<p><br></p>
<p><span style="font-size:18px;"><span style="font-size:18px;"></span></span></p>
<p><span style="font-size:18px;"><img src="https://www.icode9.com/i/?i=20170106135012602" alt=""><br></span></p>
<p><span style="font-size:18px;"></span></p>
<p><span style="font-size:18px;">通过JDK8源码javadoc，可以知道这个注解有以下特点：</span></p>
<p><span style="font-size:18px;">1、该注解只能标记在"有且仅有一个抽象方法"的接口上。</span></p>
<p><span style="font-size:18px;">2、JDK8接口中的<a href="http://blog.csdn.net/aitangyong/article/details/54134385">静态方法和默认方法</a>，都不算是抽象方法。</span></p>
<p><span style="font-size:18px;">3、接口默认继承java.lang.Object，所以如果接口显示声明覆盖了Object中方法，那么也不算抽象方法。</span></p>
<p><span style="font-size:18px;">4、该注解不是必须的，如果一个接口符合"函数式接口"定义，那么加不加该注解都没有影响。加上该注解能够更好地让编译器进行检查。如果编写的不是函数式接口，但是加上了@FunctionInterface，那么编译器会报错。</span></p>
<p><br></p>
<p><span style="font-size:18px;"><span style="font-size:18px;"><strong><span style="color:#ff0000;">@FunctionalInterface标记在接口上，“函数式接口”是指仅仅只包含一个抽象方法的接口</span></strong>。<br></span></span></p>
<p><span style="font-size:18px;"><span style="font-size:18px;"><img src="https://www.icode9.com/i/?i=20170106134212771" alt=""><br></span></span></p>
<p><span style="font-size:18px;"><span style="font-size:18px;"><br></span></span></p>
<p><span style="font-size:18px;"><span style="font-size:18px;">如果一个接口中包含不止一个抽象方法，那么不能使用@FunctionalInterface，编译会报错。</span></span></p>
<p><span style="font-size:18px;"><span style="font-size:18px;"><img src="https://www.icode9.com/i/?i=20170106134358818" alt=""><br></span></span></p>
<p><br></p>
<p><span style="font-size:18px;">比如下面这个接口就是一个正确的函数式接口：</span></p>
<pre><code class="language-java hljs"><ol class="hljs-ln"><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="1"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment">// 正确的函数式接口</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="2"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-meta">@FunctionalInterface</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="3"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">TestInterface</span> </span>{</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="4"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="5"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="6"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment">// 抽象方法</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="7"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">sub</span><span class="hljs-params">()</span></span>;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="8"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="9"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment">// java.lang.Object中的方法不是抽象方法</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="10"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">equals</span><span class="hljs-params">(Object var1)</span></span>;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="11"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="12"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment">// default不是抽象方法</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="13"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">default</span> <span class="hljs-keyword">void</span> <span class="hljs-title">defaultMethod</span><span class="hljs-params">()</span></span>{</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="14"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="15"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> }</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="16"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="17"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment">// static不是抽象方法</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="18"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">staticMethod</span><span class="hljs-params">()</span></span>{</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="19"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> }</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="21"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button {2}" data-title="复制" onclick="hljs.copyCode(event)"></div></pre>
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