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<p>今天在項目開發時遇到一個問題，整個項目是使用Spring等框架搭建起來的在運行項目時不報任何的異常信息，就是找不到某個類信息，各方查找該類確實是存在的，最後經過斷點跟蹤時在異常棧內發現java.lang.ExceptionInInitializerError這個異常信息，但這個異常信息沒有在控制檯或者日誌系統中拋出來，查明緣由以後就對症下藥最終解決了該問題。查找該問題也着實費了一翻功夫，正好趁此機會把該問題引起的緣由及針對這類問題應該如何來避免記錄一下。因爲該項目中的代碼比較複雜，這裏舉一個簡單的例子來講明一下該異常產生的緣由。</p> <p>java.lang.ExceptionInInitializerError</p> <p>該異常在Java中的繼承關係以下：</p> <p><img src="https://img-blog.csdn.net/20131118212323609?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdTAxMDM5NzM2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt=""></p> <p>下面是jdk對該異常的描述</p> <p></p> <dl><dt> </dt></dl><pre>public class <strong>ExceptionInInitializerError</strong></pre>extends <a title="java.lang 中的類" href="../../java/lang/LinkageError.html" rel="nofollow" target="_blank">LinkageError</a> <p></p> <p>靜態初始化程序中發生意外異常的信號。拋出 <code>ExceptionInInitializerError</code> 代表<span style="color:#FF0000;"><strong>在計算靜態初始值或靜態變量的初始值期間發生異常</strong></span>。 </p> <p>從版本 1.4 開始，這個異常已經更新過，符合通用異常鏈機制。「保存的 throwable 對象」多是在構造的時候提供的，而且能夠經過 <a href="../../java/lang/ExceptionInInitializerError.html#getException()" rel="nofollow" target="_blank"> <code>getException()</code></a> 方法來訪問，這類對象目前被認爲是致使異常的<em>緣由</em>，能夠經過 <a href="../../java/lang/Throwable.html#getCause()" rel="nofollow" target="_blank"> <code>Throwable.getCause()</code></a> 方法以及前面提到的「遺留方法」訪問它。 <br></p> <p>要理解這個異常還得從Java類中的靜態變量初始化過程提及，在Java類中靜態變量的初始化順序和靜態變量的聲明順序是一致的。爲了驗證該說法，咱們寫一個簡單的小程序，代碼以下：</p> <p></p><pre onclick="hljs.copyCode(event)"><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"><span class="hljs-comment">/**</span></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-comment"> * </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-comment"> */</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"><span class="hljs-keyword">package</span> com.mhy.oo.statics;</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-keyword">import</span> java.util.ArrayList;</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-keyword">import</span> java.util.List;</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"><span class="hljs-comment">/**</span></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-comment"> * <span class="hljs-doctag">@author</span> mhy2011@163.com</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"><span class="hljs-comment"> * <span class="hljs-doctag">@date</span> 2011-11-18</span></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"> */</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-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">StaticParams</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"> <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> NUM_A = getA();</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"> <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> NUM_B = getB();</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-keyword">private</span> <span class="hljs-keyword">static</span> List<String> LIST_A = getListA();</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"> </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"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-title">StaticParams</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="20"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化構造方法"</span>);</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><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="22"></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="23"></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> StaticParams <span class="hljs-title">getInstance</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="24"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> StaticParams();</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="25"></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="26"></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="27"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> <span class="hljs-title">getA</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="28"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化A"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="29"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-number">10</span>;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="30"></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="31"></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="32"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> <span class="hljs-title">getB</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="33"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化B"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="34"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-number">20</span>;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="35"></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="36"></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="37"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> List<String> <span class="hljs-title">getListA</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="38"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化List"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="39"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> ArrayList<String>();</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="40"></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="41"></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="42"></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">main</span><span class="hljs-params">(String[] args)</span> </span>{</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="43"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> StaticParams.getInstance();</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="44"></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="45"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line">}</div></div></li></ol></code><div class="hljs-button" data-title="複製"></div></pre><br> 運行該程序，輸出結果以下： <p><img src="https://img-blog.csdn.net/20131118213123906?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdTAxMDM5NzM2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt=""></p> <p>調整靜態變量NUM_A和NUM_B的聲明順序，其餘邏輯不變</p> <p><img src="https://img-blog.csdn.net/20131118213244437?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdTAxMDM5NzM2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt=""></p> <p>而後再次運行該程序，輸出結果以下：</p> <p><img src="https://img-blog.csdn.net/20131118213349531?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdTAxMDM5NzM2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt=""></p> <p>說到這，想必聰明的程序員就想到問題緣由了。即在某個靜態變量的初始化還未執行以前就使用該靜態變量。爲了模擬該問題產生緣由，咱們修改上面的代碼成一個單例模式，具體代碼以下：</p> <p></p><pre onclick="hljs.copyCode(event)"><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"><span class="hljs-comment">/**</span></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-comment"> * </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-comment"> */</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"><span class="hljs-keyword">package</span> com.mhy.oo.statics;</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-keyword">import</span> java.util.ArrayList;</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-keyword">import</span> java.util.List;</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"><span class="hljs-comment">/**</span></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-comment"> * <span class="hljs-doctag">@author</span> mhy2011@163.com</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"><span class="hljs-comment"> * <span class="hljs-doctag">@date</span> 2011-11-18</span></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"> */</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-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">StaticParams</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"> <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> StaticParams sp = buildStaticParams();</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-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> NUM_A = getA();</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-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> NUM_B = getB();</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"> <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> List<String> LIST_A = getListA();</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"> <span class="hljs-comment"><span class="hljs-comment">/**</span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="22"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * 私有化構造方法</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="23"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> */</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="24"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-title">StaticParams</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="25"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化構造方法"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="26"></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="27"></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="28"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment"><span class="hljs-comment">/**</span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="29"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * sp的聲明在其餘幾個靜態變量以前</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="30"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="31"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * <span class="hljs-doctag">@return</span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="32"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> */</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="33"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> StaticParams <span class="hljs-title">buildStaticParams</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="34"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">if</span> (<span class="hljs-keyword">null</span> == sp) {</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="35"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> sp = <span class="hljs-keyword">new</span> StaticParams();</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="36"></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="37"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">int</span> result = NUM_A * NUM_B; <span class="hljs-comment">// 基本類型有默認值，此處不會報錯，但結果不正確</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="38"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"result is :"</span> + result);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="39"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> LIST_A.add(<span class="hljs-string">"abcd"</span>); <span class="hljs-comment">//此時LIST_A還未初始化，到此有異常</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="40"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> sp;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="41"></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="42"></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="43"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-comment"><span class="hljs-comment">/**</span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="44"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * 獲取StaticParams實例</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="45"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * </span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="46"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> * <span class="hljs-doctag">@return</span></span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="47"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"><span class="hljs-comment"> */</span></div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="48"></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> StaticParams <span class="hljs-title">getInstance</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="49"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> sp;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="50"></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="51"></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="52"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> <span class="hljs-title">getA</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="53"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化A"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="54"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-number">10</span>;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="55"></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="56"></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="57"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">int</span> <span class="hljs-title">getB</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="58"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化B"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="59"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-number">20</span>;</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="60"></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="61"></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="62"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> List<String> <span class="hljs-title">getListA</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="63"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> System.out.println(<span class="hljs-string">"初始化List"</span>);</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="64"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> ArrayList<String>();</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="65"></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="66"></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="67"></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">main</span><span class="hljs-params">(String[] args)</span> </span>{</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="68"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> StaticParams.getInstance();</div></div></li><li><div class="hljs-ln-numbers"><div class="hljs-ln-line hljs-ln-n" data-line-number="69"></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="70"></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="71"></div></div><div class="hljs-ln-code"><div class="hljs-ln-line"> </div></div></li></ol></code><div class="hljs-button" data-title="複製"></div></pre><br> 在上面的例子中，sp變量初始化中使用到的其餘的變量，但其餘的靜態變量還未初始化，故而在sp初始化時就會產生上面的異常，運行上面的程序就能夠在控制檯看到以下異常信息： <p><img src="https://img-blog.csdn.net/20131118214412812?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvdTAxMDM5NzM2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt=""></p> <p>說到這裏，想必你們在編程過程當中就知道如何來避免該異常信息的產生了吧。<br></p> <p><br></p> </div>java