1. Overview

1.概述

In this tutorial, we’ll look into different ways to search for a String in an ArrayList. Our intent is to check if a specific non-empty sequence of characters is present in any of the elements in the ArrayList and to return a list with all the matching elements.

在本教程中，我们将研究在一个ArrayList中搜索一个String的不同方法。我们的目的是检查ArrayList中的任何元素是否存在一个特定的非空字符序列，并返回一个包含所有匹配元素的列表。

2. Basic Looping

2.基本循环

First, let’s use a basic loop to search the sequence of characters in the given search string using the contains method of Java’s String class:

首先，让我们使用一个基本的循环，使用Java的String类的contains方法搜索给定搜索字符串中的字符序列。

public List<String> findUsingLoop(String search, List<String> list) {
    List<String> matches = new ArrayList<String>();

    for(String str: list) {
        if (str.contains(search)) {
            matches.add(str);
        }
    }

    return matches;
}

3. Streams

3.溪流

The Java 8 Streams API provides us with a more compact solution by using functional operations.

Java 8 Streams API通过使用函数式操作为我们提供了一个更紧凑的解决方案。

First, we’ll use the filter() method to search our input list for the search string, and then, we’ll use the collect method to create and populate a list containing the matching elements:

首先，我们将使用filter()方法来搜索我们的输入列表的搜索字符串，然后，我们将使用collect方法来创建和填充一个包含匹配元素的列表。

public List<String> findUsingStream(String search, List<String> list) {
    List<String> matchingElements = list.stream()
      .filter(str -> str.trim().contains(search))
      .collect(Collectors.toList());

    return matchingElements;
}

4. Third-Party Libraries

4.第三方图书馆

If we cannot use the Java 8 Stream API, we can look at third-party libraries such as Commons Collections and Google Guava.

如果我们不能使用Java 8 Stream API，我们可以看看第三方库，如Commons Collections和Google Guava.。

To use them, we just need to add Guava, Commons Collections, or both dependencies in our pom.xml file:

要使用它们，我们只需要在我们的pom.xml文件中添加Guava、Commons Collections或两者的依赖。

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>31.0.1-jre</version>
</dependency>

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.1</version>
</dependency>

4.1. Commons Collections

4.1.公用事业集合

Commons Collections provides us with a method IterableUtils.filteredIterable() that matches the given Iterable against a Predicate.

Commons Collections为我们提供了一个方法IterableUtils.filteredIterable()，它可以将给定的Iterable与Predicate进行匹配。

Let’s call IterableUtils.filteredIterable(), defining the predicate to select only those elements containing the search string. Then, we’ll use IteratorUtils.toList() to convert the Iterable to a List:

让我们调用IterableUtils.filteredIterable()，定义谓词，只选择那些包含搜索字符串的元素。然后，我们将使用IteratorUtils.toList()来将Iterable转换为List。

public List<String> findUsingCommonsCollection(String search, List<String> list) {
    Iterable<String> result = IterableUtils.filteredIterable(list, new Predicate<String>() {
        public boolean evaluate(String listElement) {
            return listElement.contains(search);
        }
    });

    return IteratorUtils.toList(result.iterator());
}

4.2. Google Guava

Google Guava offers a similar solution to Apache’s filteredIterable() with the Iterables.filter() method. Let’s use it to filter the list and return only the elements matching our search string:

Google Guava提供了一个与Apache的filteredIterable()类似的解决方案，即Iterables.filter()方法。让我们用它来过滤列表，只返回与我们的搜索字符串匹配的元素。

public List<String> findUsingGuava(String search, List<String> list) {         
    Iterable<String> result = Iterables.filter(list, Predicates.containsPattern(search));

    return Lists.newArrayList(result.iterator());
}

5. Conclusion

5.总结

In this tutorial, we’ve learned different ways of searching for a String in an ArrayList. We first started with a simple for loop and then proceeded with an approach using the Stream API. Finally, we saw some examples using two third-party libraries — Google Guava and Commons Collections.

在本教程中，我们学习了在ArrayList中搜索String的不同方法。我们首先从一个简单的for循环开始，然后进行了使用Stream API的方法。最后，我们看到了一些使用两个第三方库的例子 – Google Guava和Commons Collections.。

The complete examples are available over on GitHub.

完整的例子可在GitHub上找到。