java编程基础数组ArrayList使用详解<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">Java编程基础中的ArrayList用于存储动态大小的元素集合。与大小固定的数组相反，ArrayList会在添加新元素时自动增大其大小。</span></span></span></p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">ArrayList是Java集合框架的一部分，它实现了Java的<code>List</code>接口。<img alt="list" class="img-thumbnail" src="/resources/assist/images/blog/3a58de20c693483dba6ea4d6a42b7e2a.jpg" /></span></span></span><br />
<br />
</p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">以下几点需要注意Java中的ArrayList -</span></span></span></p>
<ul style="margin-left:30px; margin-right:0px">
<li>
<p style="margin-left:0px; margin-right:0px">ArrayList是一个可调整大小的数组，也称为动态数组。它的尺寸越来越大，以适应新的元素，并在元素被移除时缩小尺寸。</p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">ArrayList内部使用数组来存储元素。就像数组一样，它允许您通过索引来检索元素。</p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">Java ArrayList允许重复值和空值。</p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">Java ArrayList是一个有序的集合。它维护元素的插入顺序。</p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">您不能创建原始类型，如一个ArrayList <code>int</code>，<code>chat</code>等你需要用盒装的类型，如<code>Integer</code>，<code>Character</code>，<code>Boolean</code>等。</p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">Java ArrayList不同步。如果多个线程同时尝试修改ArrayList，那么最终结果将是非确定性的。如果多个线程要修改它，你必须显式同步对ArrayList的访问。</p>
</li>
</ul>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">创建一个ArrayList并添加新的元素</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">这个例子显示：</span></span></span></p>
<ul style="margin-left:30px; margin-right:0px">
<li>如何使用<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#ArrayList--" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>ArrayList()</code></a>构造函数创建ArrayList 。</li>
<li>使用该<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#add-E-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>add()</code></a>方法向ArrayList添加新元素。</li>
</ul>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
public class CreateArrayListExample {
public static void main(String[] args) {
// Creating an ArrayList of String
List<String> animals = new ArrayList<>();
// Adding new elements to the ArrayList
animals.add("Lion");
animals.add("Tiger");
animals.add("Cat");
animals.add("Dog");
System.out.println(animals);
// Adding an element at a particular index in an ArrayList
animals.add(2, "Elephant");
System.out.println(animals);
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><br />
<span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出</span></span></span></p>
<pre>
<code class="language-html">[Lion, Tiger, Cat, Dog]
[Lion, Tiger, Elephant, Cat, Dog]</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">从另一个集合创建一个ArrayList</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">这个例子显示：</span></span></span></p>
<ul style="margin-left:30px; margin-right:0px">
<li>
<p style="margin-left:0px; margin-right:0px">如何使用<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#ArrayList-java.util.Collection-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>ArrayList(Collection c)</code></a>构造函数从另一个ArrayList创建一个ArrayList 。</p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">如何使用该<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#addAll-java.util.Collection-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>addAll()</code></a>方法将现有ArrayList中的所有元素添加到新的ArrayList中。</p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
public class CreateArrayListFromCollectionExample {
public static void main(String[] args) {
List<Integer> firstFivePrimeNumbers = new ArrayList<>();
firstFivePrimeNumbers.add(2);
firstFivePrimeNumbers.add(3);
firstFivePrimeNumbers.add(5);
firstFivePrimeNumbers.add(7);
firstFivePrimeNumbers.add(11);
// Creating an ArrayList from another collection
List<Integer> firstTenPrimeNumbers = new ArrayList<>(firstFivePrimeNumbers);
List<Integer> nextFivePrimeNumbers = new ArrayList<>();
nextFivePrimeNumbers.add(13);
nextFivePrimeNumbers.add(17);
nextFivePrimeNumbers.add(19);
nextFivePrimeNumbers.add(23);
nextFivePrimeNumbers.add(29);
// Adding an entire collection to an ArrayList
firstTenPrimeNumbers.addAll(nextFivePrimeNumbers);
System.out.println(firstTenPrimeNumbers);
}
}</code></pre>
</li>
</ul>
<p style="margin-left:0px; margin-right:0px; text-align:start"><br />
<span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出：</span></span></span></p>
<pre>
<code class="language-html">[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">访问ArrayList中的元素</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">这个例子显示：</span></span></span></p>
<ul style="margin-left:30px; margin-right:0px">
<li>如何使用该<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#isEmpty--" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>isEmpty()</code></a>方法检查ArrayList是否为空。</li>
<li>如何使用该<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#size--" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>size()</code></a>方法找到ArrayList的大小。</li>
<li>如何使用该<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#get-int-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>get()</code></a>方法访问ArrayList中特定索引处的元素。</li>
<li>如何使用该<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#set-int-E-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>set()</code></a>方法修改ArrayList中特定索引处的元素。</li>
</ul>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
public class AccessElementsFromArrayListExample {
public static void main(String[] args) {
List<String> topCompanies = new ArrayList<>();
// Check is an ArrayList is empty
System.out.println("Is the topCompanies list empty? : " + topCompanies.isEmpty());
topCompanies.add("Google");
topCompanies.add("Apple");
topCompanies.add("Microsoft");
topCompanies.add("Amazon");
topCompanies.add("Facebook");
// Find the size of an ArrayList
System.out.println("Here are the top " + topCompanies.size() + " companies in the world");
System.out.println(topCompanies);
// Retrieve the element at a given index
String bestCompany = topCompanies.get(0);
String secondBestCompany = topCompanies.get(1);
String lastCompany = topCompanies.get(topCompanies.size() - 1);
System.out.println("Best Company: " + bestCompany);
System.out.println("Second Best Company: " + secondBestCompany);
System.out.println("Last Company in the list: " + lastCompany);
// Modify the element at a given index
topCompanies.set(4, "Walmart");
System.out.println("Modified top companies list: " + topCompanies);
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">Is the topCompanies list empty? : true
Here are the top 5 companies in the world
[Google, Apple, Microsoft, Amazon, Facebook]
Best Company: Google
Second Best Company: Apple
Last Company in the list: Facebook
Modified top companies list: [Google, Apple, Microsoft, Amazon, Walmart]</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">从ArrayList中移除元素</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">这个例子显示：</span></span></span></p>
<ol style="margin-left:30px; margin-right:0px">
<li>
<p style="margin-left:0px; margin-right:0px">如何删除ArrayList |中给定索引处的元素 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#remove-java.lang.Object-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">delete</a><a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#remove-int-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">（int索引）</a></p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">如何从ArrayList |中删除元素 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#remove-java.lang.Object-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">delete（Object o）</a></p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">如何从给定集合中存在的ArrayList中移除所有元素| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#remove-java.lang.Object-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">delete</a>All<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#removeAll-java.util.Collection-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">（）</a></p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">如何删除所有匹配给定谓词|的元素 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#removeIf-java.util.function.Predicate-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">removeIf（）</a></p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">如何清除ArrayList | <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#clear--" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">clear（）</a></p>
</li>
</ol>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
public class RemoveElementsFromArrayListExample {
public static void main(String[] args) {
List<String> programmingLanguages = new ArrayList<>();
programmingLanguages.add("C");
programmingLanguages.add("C++");
programmingLanguages.add("Java");
programmingLanguages.add("Kotlin");
programmingLanguages.add("Python");
programmingLanguages.add("Perl");
programmingLanguages.add("Ruby");
System.out.println("Initial List: " + programmingLanguages);
// Remove the element at index `5`
programmingLanguages.remove(5);
System.out.println("After remove(5): " + programmingLanguages);
// Remove the element "Kotlin" (The remove() method returns false if the element does not exist in the ArrayList)
boolean isRemoved = programmingLanguages.remove("Kotlin");
System.out.println("After remove(\"Kotlin\"): " + programmingLanguages);
// Remove all the elements belonging to the collection scriptingLanguages
List<String> scriptingLanguages = new ArrayList<>();
scriptingLanguages.add("Python");
scriptingLanguages.add("Ruby");
scriptingLanguages.add("Perl");
programmingLanguages.removeAll(scriptingLanguages);
System.out.println("After removeAll(scriptingLanguages): " + programmingLanguages);
// Remove all the elements that satisfy the given predicate
programmingLanguages.removeIf(new Predicate<String>() {
@Override
public boolean test(String s) {
return s.startsWith("C");
}
});
/*
The above removeIf() call can also be written using lambda expression like this -
programmingLanguages.removeIf(s -> s.startsWith("C"))
*/
System.out.println("After Removing all elements that start with \"C\": " + programmingLanguages);
// Remove all elements from the ArrayList
programmingLanguages.clear();
System.out.println("After clear(): " + programmingLanguages);
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">Initial List: [C, C++, Java, Kotlin, Python, Perl, Ruby]
After remove(5): [C, C++, Java, Kotlin, Python, Ruby]
After remove("Kotlin"): [C, C++, Java, Python, Ruby]
After removeAll(scriptingLanguages): [C, C++, Java]
After Removing all elements that start with "C": [Java]
After clear(): []</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">迭代ArrayList</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">以下示例显示如何使用迭代遍历ArrayList</span></span></span></p>
<ol style="margin-left:30px; margin-right:0px">
<li>Java 8 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#forEach-java.util.function.Consumer-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>forEach</code></a>循环。</li>
<li><a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#iterator--" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>iterator()</code></a>。</li>
<li><a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#iterator--" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>iterator()</code></a>和Java 8 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html#forEachRemaining-java.util.function.Consumer-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">forEachRemaining（）</a>方法。</li>
<li><a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#listIterator-int-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>listIterator()</code></a>。</li>
<li>每个循环都很简单。</li>
<li>用索引循环。</li>
</ol>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
public class IterateOverArrayListExample {
public static void main(String[] args) {
List<String> tvShows = new ArrayList<>();
tvShows.add("Breaking Bad");
tvShows.add("Game Of Thrones");
tvShows.add("Friends");
tvShows.add("Prison break");
System.out.println("=== Iterate using Java 8 forEach loop ===");
tvShows.forEach(tvShow -> {
System.out.println(tvShow);
});
System.out.println("\n=== Iterate using an iterator() ===");
Iterator<String> tvShowIterator = tvShows.iterator();
while (tvShowIterator.hasNext()) {
String tvShow = tvShowIterator.next();
System.out.println(tvShow);
}
System.out.println("\n=== Iterate using an iterator() and Java 8 forEachRemaining() method ===");
tvShowIterator = tvShows.iterator();
tvShowIterator.forEachRemaining(tvShow -> {
System.out.println(tvShow);
});
System.out.println("\n=== Iterate using a listIterator() to traverse in both directions ===");
// Here, we start from the end of the list and traverse backwards.
ListIterator<String> tvShowListIterator = tvShows.listIterator(tvShows.size());
while (tvShowListIterator.hasPrevious()) {
String tvShow = tvShowListIterator.previous();
System.out.println(tvShow);
}
System.out.println("\n=== Iterate using simple for-each loop ===");
for(String tvShow: tvShows) {
System.out.println(tvShow);
}
System.out.println("\n=== Iterate using for loop with index ===");
for(int i = 0; i < tvShows.size(); i++) {
System.out.println(tvShows.get(i));
}
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出：</span></span></span></p>
<pre>
<code class="language-html">=== Iterate using Java 8 forEach loop ===
Breaking Bad
Game Of Thrones
Friends
Prison break
=== Iterate using an iterator() ===
Breaking Bad
Game Of Thrones
Friends
Prison break
=== Iterate using an iterator() and Java 8 forEachRemaining() method ===
Breaking Bad
Game Of Thrones
Friends
Prison break
=== Iterate using a listIterator() to traverse in both directions ===
Prison break
Friends
Game Of Thrones
Breaking Bad
=== Iterate using simple for-each loop ===
Breaking Bad
Game Of Thrones
Friends
Prison break
=== Iterate using for loop with index ===
Breaking Bad
Game Of Thrones
Friends
Prison break</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">在遍历期间需要修改ArrayList时，<code>iterator()</code>和<code>listIterator()</code>方法很有用。</span></span></span></p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">考虑下面的例子，在<code>iterator.remove()</code>遍历它的时候我们使用方法从ArrayList中移除元素-</span></span></span></p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class ArrayListIteratorRemoveExample {
public static void main(String[] args) {
List<Integer> numbers = new ArrayList<>();
numbers.add(13);
numbers.add(18);
numbers.add(25);
numbers.add(40);
Iterator<Integer> numbersIterator = numbers.iterator();
while (numbersIterator.hasNext()) {
Integer num = numbersIterator.next();
if(num % 2 != 0) {
numbersIterator.remove();
}
}
System.out.println(numbers);
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">[18, 40]</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">在ArrayList中搜索元素</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">下面的例子显示了如何：</span></span></span></p>
<ul style="margin-left:30px; margin-right:0px">
<li>
<p style="margin-left:0px; margin-right:0px">检查ArrayList是否包含给定的元素| <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#contains-java.lang.Object-" rel="external nofollow" target="_blank">contains</a><a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#contains-java.lang.Object-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">（）</a></p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">查找ArrayList |中第一次出现元素的索引 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#indexOf-java.lang.Object-" rel="external nofollow" target="_blank">indexOf</a><a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#indexOf-java.lang.Object-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">（）</a></p>
</li>
<li>
<p style="margin-left:0px; margin-right:0px">查找ArrayList |中最后一次出现元素的索引 <a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#lastIndexOf-java.lang.Object-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank">lastIndexOf（）</a></p>
</li>
</ul>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
public class SearchElementsInArrayListExample {
public static void main(String[] args) {
List<String> names = new ArrayList<>();
names.add("John");
names.add("Alice");
names.add("Bob");
names.add("Steve");
names.add("John");
names.add("Steve");
names.add("Maria");
// Check if an ArrayList contains a given element
System.out.println("Does names array contain \"Bob\"? : " + names.contains("Bob"));
// Find the index of first occurrence of an element in an ArrayList
System.out.println("indexOf \"Steve\": " + names.indexOf("Steve"));
System.out.println("indexOf \"Mark\": " + names.indexOf("Mark"));
// Find the index of the last occurrence of an element in an ArrayList
System.out.println("lastIndexOf \"John\" : " + names.lastIndexOf("John"));
System.out.println("lastIndexOf \"Bill\" : " + names.lastIndexOf("Bill"));
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">Does names array contain "Bob"? : true
indexOf "Steve": 3
indexOf "Mark": -1
lastIndexOf "John" : 4
lastIndexOf "Bill" : -1</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">用户定义对象的ArrayList</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">由于ArrayList支持泛型，因此可以创建<strong>任何</strong>类型的ArrayList 。它可以是简单的类型，如<code>Integer</code>，<code>String</code>，<code>Double</code>或复杂类型等的ArrayLists的ArrayList，或包含HashMap的ArrayList或任何用户定义的对象的ArrayList。</span></span></span></p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">在以下示例中，您将学习如何创建用户定义对象的ArrayList。</span></span></span></p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
class User {
private String name;
private int age;
public User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
public class ArrayListUserDefinedObjectExample {
public static void main(String[] args) {
List<User> users = new ArrayList<>();
users.add(new User("Rajeev", 25));
users.add(new User("John", 34));
users.add(new User("Steve", 29));
users.forEach(user -> {
System.out.println("Name : " + user.getName() + ", Age : " + user.getAge());
});
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">Name : Rajeev, Age : 25
Name : John, Age : 34
Name : Steve, Age : 29</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">排序ArrayList</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">对ArrayList进行排序是您在程序中遇到的一个非常常见的任务。在本节中，我会告诉你如何 -</span></span></span></p>
<ul style="margin-left:30px; margin-right:0px">
<li>使用<a href="https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#sort-java.util.List-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>Collections.sort()</code></a>方法对ArrayList进行排序。</li>
<li>使用<a href="https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#sort-java.util.Comparator-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>ArrayList.sort()</code></a>方法对ArrayList进行排序。</li>
<li>用自定义比较器对用户定义对象的ArrayList进行排序。</li>
</ul>
<h4 style="margin-left:0px; margin-right:0px; text-align:start">1.使用Collections.sort（）方法对ArrayList进行排序</h4>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class ArrayListCollectionsSortExample {
public static void main(String[] args) {
List<Integer> numbers = new ArrayList<>();
numbers.add(13);
numbers.add(7);
numbers.add(18);
numbers.add(5);
numbers.add(2);
System.out.println("Before : " + numbers);
// Sorting an ArrayList using Collections.sort() method
Collections.sort(numbers);
System.out.println("After : " + numbers);
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">Before : [13, 7, 18, 5, 2]
After : [2, 5, 7, 13, 18]</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start">2.使用ArrayList.sort（）方法对ArrayList排序<br />
</p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public class ArrayListSortExample {
public static void main(String[] args) {
List<String> names = new ArrayList<>();
names.add("Lisa");
names.add("Jennifer");
names.add("Mark");
names.add("David");
System.out.println("Names : " + names);
// Sort an ArrayList using its sort() method. You must pass a Comparator to the ArrayList.sort() method.
names.sort(new Comparator<String>() {
@Override
public int compare(String name1, String name2) {
return name1.compareTo(name2);
}
});
// The above `sort()` method call can also be written simply using lambda expressions
names.sort((name1, name2) -> name1.compareTo(name2));
// Following is an even more concise solution
names.sort(Comparator.naturalOrder());
System.out.println("Sorted Names : " + names);
}
}</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">输出:</span></span></span></p>
<pre>
<code class="language-html">Names : [Lisa, Jennifer, Mark, David]
Sorted Names : [David, Jennifer, Lisa, Mark]</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start">3.使用自定义比较器对对象的ArrayList进行排序<br />
</p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
class Person {
private String name;
private Integer age;
public Person(String name, Integer age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public String toString() {
return "{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
public class ArrayListObjectSortExample {
public static void main(String[] args) {
List<Person> people = new ArrayList<>();
people.add(new Person("Sachin", 47));
people.add(new Person("Chris", 34));
people.add(new Person("Rajeev", 25));
people.add(new Person("David", 31));
System.out.println("Person List : " + people);
// Sort People by their Age
people.sort((person1, person2) -> {
return person1.getAge() - person2.getAge();
});
// A more concise way of writing the above sorting function
people.sort(Comparator.comparingInt(Person::getAge));
System.out.println("Sorted Person List by Age : " + people);
// You can also sort using Collections.sort() method by passing the custom Comparator
Collections.sort(people, Comparator.comparing(Person::getName));
System.out.println("Sorted Person List by Name : " + people);
}
}</code></pre>
输出:
<pre>
<code class="language-html">Person List : [{name='Sachin', age=47}, {name='Chris', age=34}, {name='Rajeev', age=25}, {name='David', age=31}]
Sorted Person List by Age : [{name='Rajeev', age=25}, {name='David', age=31}, {name='Chris', age=34}, {name='Sachin', age=47}]
Sorted Person List by Name : [{name='Chris', age=34}, {name='David', age=31}, {name='Rajeev', age=25}, {name='Sachin', age=47}]</code></pre>
<h2 style="margin-left:0px; margin-right:0px; text-align:start">同步对ArrayList的访问</h2>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">ArrayList类不同步。如果多个线程同时尝试修改一个ArrayList，那么最终的结果变得不确定，因为一个线程可能会覆盖另一个线程所做的更改。</span></span></span></p>
<h4 style="margin-left:0px; margin-right:0px; text-align:start">示例演示ArrayList在多线程环境中的不可预知行为</h4>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">以下示例显示了当多个线程同时尝试修改ArrayList时发生的情况。</span></span></span></p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class UnsafeArrayListExample {
public static void main(String[] args) throws InterruptedException {
List<Integer> unsafeArrayList = new ArrayList<>();
unsafeArrayList.add(1);
unsafeArrayList.add(2);
unsafeArrayList.add(3);
// Create a thread pool of size 10
ExecutorService executorService = Executors.newFixedThreadPool(10);
// Create a Runnable task that increments the each element of the ArrayList by one
Runnable task = () -> {
incrementArrayList(unsafeArrayList);
};
// Submit the task to the executor service 100 times.
// All the tasks will modify the ArrayList concurrently
for(int i = 0; i < 100; i++) {
executorService.submit(task);
}
executorService.shutdown();
executorService.awaitTermination(60, TimeUnit.SECONDS);
System.out.println(unsafeArrayList);
}
// Increment all the values in the ArrayList by one
private static void incrementArrayList(List<Integer> unsafeArrayList) {
for(int i = 0; i < unsafeArrayList.size(); i++) {
Integer value = unsafeArrayList.get(i);
unsafeArrayList.set(i, value + 1);
}
}
}</code></pre>
上述程序的最终输出应该相等，<code>[101, 102, 103]</code>因为我们将ArrayList中的值增加了100次。但是如果你运行这个程序，它会在每次运行时产生不同的输出 -<br />
输出:
<pre>
<code class="language-html">[96, 96, 98]</code></pre>
<h4 style="margin-left:0px; margin-right:0px; text-align:start">演示如何将并发修改同步到ArrayList的示例</h4>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">好吧！现在让我们看看我们如何<code>ArrayList</code>在多线程环境中同步访问。</span></span></span></p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">以下示例显示了上一个示例的同步版本。与以前的程序不同，该程序的输出是确定性的，并且始终是相同的。</span></span></span></p>
<pre>
<code class="language-java">import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class SynchronizedArrayListExample {
public static void main(String[] args) throws InterruptedException {
List<Integer> safeArrayList = Collections.synchronizedList(new ArrayList<>());
safeArrayList.add(1);
safeArrayList.add(2);
safeArrayList.add(3);
// Create a thread pool of size 10
ExecutorService executorService = Executors.newFixedThreadPool(10);
// Create a Runnable task that increments the each element of the ArrayList by one
Runnable task = () -> {
incrementArrayList(safeArrayList);
};
// Submit the task to the executor service 100 times.
// All the tasks will modify the ArrayList concurrently
for(int i = 0; i < 100; i++) {
executorService.submit(task);
}
executorService.shutdown();
executorService.awaitTermination(60, TimeUnit.SECONDS);
System.out.println(safeArrayList);
}
// Increment all the values in the ArrayList by one
private static void incrementArrayList(List<Integer> safeArrayList) {
synchronized (safeArrayList) {
for (int i = 0; i < safeArrayList.size(); i++) {
Integer value = safeArrayList.get(i);
safeArrayList.set(i, value + 1);
}
}
}
}</code></pre>
输出:
<pre>
<code class="language-html">[101, 102, 103]</code></pre>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">以上示例使用<a href="https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#synchronizedList-java.util.List-" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>Collections.synchronizedList()</code></a>方法来获取ArrayList的同步视图。</span></span></span></p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff">而且，对<code>incrementArrayList()</code>方法内的ArrayList的修改被封装在一个<code>synchronized</code>块中。这确保了两个线程不能同时增加ArrayList元素。</span></span></span></p>
<p style="margin-left:0px; margin-right:0px; text-align:start"><span style="color:rgba(0, 0, 0, 0.87)"><span style="font-family:"Open Sans","Helvetica Neue",Helvetica,Arial,sans-serif"><span style="background-color:#ffffff"><em><a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CopyOnWriteArrayList.html" rel="external nofollow" style="box-sizing:border-box; color:#419be8; text-decoration:none; word-wrap:break-word" target="_blank"><code>CopyOnWriteArrayList</code></a>如果你需要线程安全，你也可以使用。它是ArrayList类的线程安全版本。它通过创建ArrayList的新副本来实现所有的变异操作。</em></span></span></span></p>