<ruby id="bdb3f"></ruby>

    <p id="bdb3f"><cite id="bdb3f"></cite></p>

      <p id="bdb3f"><cite id="bdb3f"><th id="bdb3f"></th></cite></p><p id="bdb3f"></p>
        <p id="bdb3f"><cite id="bdb3f"></cite></p>

          <pre id="bdb3f"></pre>
          <pre id="bdb3f"><del id="bdb3f"><thead id="bdb3f"></thead></del></pre>

          <ruby id="bdb3f"><mark id="bdb3f"></mark></ruby><ruby id="bdb3f"></ruby>
          <pre id="bdb3f"><pre id="bdb3f"><mark id="bdb3f"></mark></pre></pre><output id="bdb3f"></output><p id="bdb3f"></p><p id="bdb3f"></p>

          <pre id="bdb3f"><del id="bdb3f"><progress id="bdb3f"></progress></del></pre>

                <ruby id="bdb3f"></ruby>

                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                # 如何在 Java 中清空`ArrayList` > 原文: [https://beginnersbook.com/2013/12/how-to-empty-an-arraylist-in-java/](https://beginnersbook.com/2013/12/how-to-empty-an-arraylist-in-java/) 有兩種方法可以清空`ArrayList` - 使用 [`ArrayList.clear()`](https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#clear())方法或借助 [`ArrayList.removeAll()`](https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#removeAll(java.util.Collection))方法。盡管兩種方法都執行相同的任務,但它們清空`List`的方式卻截然不同。 讓我們先看下面的例子,然后我們將看到`clear()`和`removeAll()`之間的實現和區別。 ```java package beginnersbook.com; import java.util.ArrayList; import java.io.*; public class Details { public static void main(String [] args) { ArrayList<String> al1=new ArrayList<String>(); al1.add("abc"); al1.add("xyz"); System.out.println("ArrayList before clear: "+al1); al1.clear(); System.out.println("ArrayList after clear: "+al1); ArrayList<String> al2=new ArrayList<String>(); al2.add("text 1"); al2.add("text 2"); System.out.println("ArrayList before removeAll: "+al2); al2.removeAll(al2); System.out.println("ArrayList before removeAll: "+al2); } } ``` 輸出: ```java ArrayList before clear: [abc, xyz] ArrayList after clear: [] ArrayList before removeAll: [text 1="text" 2="2" language="1,"][/text] ArrayList before removeAll: [] ``` 因為你們兩個方法都可以完成相同的工作,所以它們會清空`ArrayList`。是時候確定哪種方法可以提供良好的性能。 `clear()`方法的實際代碼: ```java public void clear() { for (int i = 0; i < size; i++) arraylist[i] = null; size = 0; } ``` 這里`arraylist`是`ArrayList`類的一個實例。 代碼`removeAll()`方法: ```java public boolean removeAll(Collection c) { boolean ismodified = false; Iterator iterator = iterator(); while (iterator.hasNext()) { if (c.contains(iterator.next())) { iterator.remove(); ismodified = true; } } return ismodified; } ``` 通過查看這兩種方法的代碼,我們可以很好地說,與`removeAll()`方法相比,`clear()`方法提供了更好的性能。 `clear`的性能:`O(n)` `removeAll`的性能:`O(n^2)`
                  <ruby id="bdb3f"></ruby>

                  <p id="bdb3f"><cite id="bdb3f"></cite></p>

                    <p id="bdb3f"><cite id="bdb3f"><th id="bdb3f"></th></cite></p><p id="bdb3f"></p>
                      <p id="bdb3f"><cite id="bdb3f"></cite></p>

                        <pre id="bdb3f"></pre>
                        <pre id="bdb3f"><del id="bdb3f"><thead id="bdb3f"></thead></del></pre>

                        <ruby id="bdb3f"><mark id="bdb3f"></mark></ruby><ruby id="bdb3f"></ruby>
                        <pre id="bdb3f"><pre id="bdb3f"><mark id="bdb3f"></mark></pre></pre><output id="bdb3f"></output><p id="bdb3f"></p><p id="bdb3f"></p>

                        <pre id="bdb3f"><del id="bdb3f"><progress id="bdb3f"></progress></del></pre>

                              <ruby id="bdb3f"></ruby>

                              哎呀哎呀视频在线观看