java.util.HashSet add（E e）

桃扇骨 2023-10-04 10:18 6阅读 0赞

### [java.util.HashSet][] add（E e） ###

### 描述 ###

在本文档中，我们将显示一个有关 **如何使用HashSet Class的add（）方法的**Java示例。基本上，此方法提供了将元素添加到HashSet对象的功能。返回的布尔值将指示添加元素是否成功，如果添加成功，则返回true，否则返回false。如果HashSet已包含与我们要添加的内容相同的返回值，则返回false。请注意，HashSet未排序，因此元素的顺序是随机的，因此请更好地注意此概念。

作为大多数Collection类的HashSet使用泛型，因此，如果我们像HashSet set = new HashSet（）那样声明集合，则集合内部的元素为String类型。而且，除非它是对象声明的子类，否则我们不能插入其他对象类型，否则将引发运行时错误。

HashSet元素是唯一的，将不会存在两个相同的元素。

**add（）方法的重要说明：**

*  由接口Collection <E>中的add指定
 *  由接口Set <E>中的add指定
 *  重写在类AbstractCollection <E>中添加

### 方法语法 ###

> public boolean add（E e）

### 方法参数 ###

<table> 
 <thead> 
  <tr> 
   <th>数据类型</th> 
   <th>范围</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Ë</td> 
   <td>Ë</td> 
   <td>要添加到此集合中的元素</td> 
  </tr> 
 </tbody> 
</table>

### 方法返回 ###

如果此集合尚未包含指定的元素，则add（E e）方法将返回true。

### 兼容性 ###

> 需要Java 1.2及更高版本

### Java HashSet add（）示例 ###

以下是一个Java代码，演示了**HashSet类**的**add（）方法**的使用**。**给出的示例可能很简单，但是它显示了add（）方法的行为。

A Java Example on how to use add(E e) method

Java

<table style="margin-left:0px;"> 
 <tbody> 
  <tr> 
   <td style="vertical-align:top;"> 
    <div style="margin-left:0px;"> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">1</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">2</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">3</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">4</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">5</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">6</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">7</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">8</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">9</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">10</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">11</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">12</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">13</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">14</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">15</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">16</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">17</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">18</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">19</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">20</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">21</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">22</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">23</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">24</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">25</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">26</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">27</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">28</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">29</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">30</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">31</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">32</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">33</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">34</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">35</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">36</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">37</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">38</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">39</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">40</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">41</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">42</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">43</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">44</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">45</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">46</span></span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">47</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;"><span style="color:#000000;">48</span></span> 
     </div> 
    </div> </td> 
   <td style="vertical-align:top;width:583.333px;"> 
    <div style="margin-left:0px;"> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">package com.javatutorialhq.java.examples;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">import static java.lang.System.*;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">import java.util.HashSet;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">/*</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">* This example source code demonstrates the use of&nbsp;&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">* add() method of HashSet class</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">*/</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">public class HashSetAddExample { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">public static void main(String[] args) throws InterruptedException { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">// get the HashMap object from the method init()</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">HashSet studentSet = init();</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">// add a few more elements</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">boolean result = studentSet.add("Darwin Villalobos");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">if (result) { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">out.println("Successfull added");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">} else { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">out.println("Operation failed");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">}</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">// add an element that is already existing</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">result = studentSet.add("Darwin Villalobos");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">if (result) { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">out.println("Successfull added");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">} else { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">out.println("Operation failed");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">}</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">}</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">private static HashSet init() { </span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">// declare the HashSet object</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">HashSet studentSet = new HashSet<span style="color:#006fe0;">&lt;</span><span style="color:#006fe0;">&gt;</span>();</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">// put contents to our HashMap</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">studentSet.add("Shyra Travis");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">studentSet.add("Sharon Wallace");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">studentSet.add("Leo Batista");</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">return studentSet;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">}</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">&nbsp;</span> 
     </div> 
     <div style="margin-left:0px;"> 
      <span style="color:#000000;">}</span> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

在上面的示例中创建了两种方法，main（）和init。main方法调用init（），该init（）初始化并将值分配给HashSet对象。main（）方法通过init（）方法将返回的对象分配给新的HashSet对象。通过调用add方法将新元素添加到集合中。根据返回的值，我们评估了插入是否成功。如果结果为假，则我们要添加的元素已经存在。记下此行为。

### 样本输出 ###

下面是运行上述示例时的示例输出。

![20210409195628630.gif][]

[java.util.HashSet]: https://javatutorialhq.com/java/util/hashset-class-tutorial/
[20210409195628630.gif]: https://img-blog.csdnimg.cn/20210409195628630.gif