Converting Iterable to Collection in Java – 在Java中把Iterable转换为集合

1. Overview

1.概述

In this tutorial, we’ll explore different ways to convert an Iterable to a Collection in Java.

在本教程中，我们将探讨在Java中把Iterable转换为Collection的不同方法。

We’ll start with plain Java solutions, then have a look at the options that the Guava and Apache Commons libraries also provide.

我们将从普通的Java解决方案开始，然后看看Guava和Apache Commons库也提供的选项。

2. Iterable and Iterator

2.Iterable和Iterator

First, we’ll define our Iterable:

首先，我们将定义我们的Iterable。

Iterable<String> iterable = Arrays.asList("john", "tom", "jane");

We’ll also define a simple Iterator – to highlight the difference between converting Iterable to Collection and Iterator to Collection:

我们还将定义一个简单的Iterator–以强调将Iterable转换为Collection和Iterator转换为Collection之间的区别。

Iterator<String> iterator = iterable.iterator();

3. Using Plain Java

3.使用普通的Java

3.1. Iterable to Collection

3.1.Iterable到Collection

We can use the Java 8 forEach() method to add all elements to the List:

我们可以使用Java 8的forEach()方法，将所有元素添加到List。

@Test
public void whenConvertIterableToListUsingJava8_thenSuccess() {
    List<String> result = new ArrayList<String>();
    iterable.forEach(result::add);

    assertThat(result, contains("john", "tom", "jane"));
}

Or use the Spliterator class to convert our Iterable to Stream then to Collection:

或者使用Spliterator类将我们的Iterable转换成Stream，然后再转换成Collection。

List<String> result = 
  StreamSupport.stream(iterable.spliterator(), false)
    .collect(Collectors.toList());

3.2. Iterator to Collection

3.2.Iterator到Collection

On the other hand, instead of using forEach(), we’ll use forEachRemaining() with Iterator:

另一方面，我们不使用forEach()，而是使用forEachRemaining()与Iterator。

@Test
public void whenConvertIteratorToListUsingJava8_thenSuccess() {
    List<String> result = new ArrayList<String>();
    iterator.forEachRemaining(result::add);

    assertThat(result, contains("john", "tom", "jane"));
}

We can also create a Spliterator from our Iterator then use it to convert Iterator to Stream:

我们也可以从我们的Iterator创建一个Spliterator，然后用它来将Iterator转换为Stream。

List<String> result = 
  StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false)
    .collect(Collectors.toList());

3.3. Using a For-Loop

3.3.使用For-Loop

Let’s also have a look at a solution that uses a very simple for-loop to convert our Iterable to a List:

我们也来看看一个解决方案，它使用一个非常简单的for-loop来将我们的Iterable转换为List。

@Test
public void whenConvertIterableToListUsingJava_thenSuccess() {
    List<String> result = new ArrayList<String>();
    for (String str : iterable) {
        result.add(str);
    }

    assertThat(result, contains("john", "tom", "jane"));
}

On the other hand, we’ll use hasNext() and next() with the Iterator:

另一方面，我们将使用hasNext()和next()与Iterator。

@Test
public void whenConvertIteratorToListUsingJava_thenSuccess() {
    List<String> result = new ArrayList<String>();
    while (iterator.hasNext()) {
        result.add(iterator.next());
    }

    assertThat(result, contains("john", "tom", "jane"));
}

4. Using Guava

4.使用番石榴

There are also a few libraries available that provide convenient methods to help us achieve this.

也有一些库可以提供方便的方法来帮助我们实现这一目标。

Let’s see how we can use Guava to convert from an Iterable to a List:

让我们看看如何使用Guava来从Iterable转换到List。

We can create a new List from Iterable or Iterator using Lists.newArrayList():

我们可以使用Lists.newArrayList()从Iterable或Iterator创建一个新的List：。

List<String> result = Lists.newArrayList(iterable);

Or we can use ImmutableList.copyOf():

或者我们可以使用ImmutableList.copyOf()。

List<String> result = ImmutableList.copyOf(iterable);

5. Using Apache Commons

5.使用Apache Commons

Finally, we’ll use Apache Commons IterableUtils to create a List from Iterable:

最后，我们将使用Apache CommonsIterableUtils，从Iterable创建一个List：

List<String> result = IterableUtils.toList(iterable);

Similarly, we’ll use IteratorUtils to create a List from our Iterator:

同样地，我们将使用IteratorUtils从我们的Iterator创建一个List。

List<String> result = IteratorUtils.toList(iterator);

6. Conclusion

6.结论

In this short article, we learned how to convert an Iterable and Iterator to a Collection using Java. We explored different ways using plain Java, and two external libraries: Guava and Apache Commons.

在这篇短文中，我们学习了如何使用Java将Iterable和Iterator转换成Collection。我们探索了使用普通Java和两个外部库的不同方法。Guava和Apache Commons。

As always, the full source code is available over on GitHub.

一如既往，完整的源代码可以在GitHub上获得。