Guava – Lists – 番石榴 – 列表

最后修改: 2014年 11月 2日

1. Overview


In this tutorial – we will illustrate the most common and useful ways to work with Lists using the Guava library.


Let’s start simple – and take a look at just creating a new ArrayList using Guava syntax – without new:


List<String> names = Lists.newArrayList("John", "Adam", "Jane");

2. Reverse a List


First, let’s reverse a List using Lists.reverse() as in the following example:


public void whenReverseList_thenReversed() {
    List<String> names = Lists.newArrayList("John", "Adam", "Jane");

    List<String> reversed = Lists.reverse(names);
    assertThat(reversed, contains("Jane", "Adam", "John"));

3. Generate Character List from a String


Now – let’s see how to break a String apart into a list of Characters.


In the following example – we use the Lists.CharactersOf() API to create a Character List from a String “John”:

在下面的例子中,我们使用Lists.CharactersOf() API从String “John”创建一个Character List

public void whenCreateCharacterListFromString_thenCreated() {
    List<Character> chars = Lists.charactersOf("John");

    assertEquals(4, chars.size());
    assertThat(chars, contains('J', 'o', 'h', 'n'));

4. Partition a List


Next – Let’s see how to partition a List.


In the following example – we use Lists.partition() to get consecutive sublists each of size two:


public void whenPartitionList_thenPartitioned(){
    List<String> names = Lists.newArrayList("John","Jane","Adam","Tom","Viki","Tyler");

    List<List<String>> result = Lists.partition(names, 2);

    assertEquals(3, result.size());
    assertThat(result.get(0), contains("John", "Jane"));
    assertThat(result.get(1), contains("Adam", "Tom"));
    assertThat(result.get(2), contains("Viki", "Tyler"));

5. Remove Duplicates From List


Now – let’s use a simple trick to remove duplicates from a List.


In the following example – we copy the elements into a Set and then we create a List back out of the remaining elements:


public void whenRemoveDuplicatesFromList_thenRemoved() {
    List<Character> chars = Lists.newArrayList('h','e','l','l','o');
    assertEquals(5, chars.size());

    List<Character> result = ImmutableSet.copyOf(chars).asList();
    assertThat(result, contains('h', 'e', 'l', 'o'));

6. Remove Null Values from List


Next – let’s see how to remove null values from a List.


In the following example – we remove all null values using the highly useful Iterables.removeIf() API and a predicate provided by the library itself:

在下面的例子中,我们使用非常有用的Iterables.removeIf() API和库本身提供的谓词来删除所有null值。

public void whenRemoveNullFromList_thenRemoved() {
    List<String> names = Lists.newArrayList("John", null, "Adam", null, "Jane");
    Iterables.removeIf(names, Predicates.isNull());

    assertEquals(3, names.size());
    assertThat(names, contains("John", "Adam", "Jane"));

7. Convert a List to an ImmutableList


Finally – let’s see how to create an immutable copy of a List – an ImmutableList – using the ImmutableList.copyOf() API:

最后–让我们看看如何使用ImmutableList.copyOf() API来创建一个List的不可变副本–ImmutableList

public void whenCreateImmutableList_thenCreated() {
    List<String> names = Lists.newArrayList("John", "Adam", "Jane");

    assertEquals(4, names.size());

    ImmutableList<String> immutable = ImmutableList.copyOf(names);
    assertThat(immutable, contains("John", "Adam", "Jane", "Tom"));

8. Conclusion


And here we are – a quick tutorial going over most of the useful things you can do with Lists using Guava.


To dig into Lists even further, check out the Predicates and Functions guide to lists as well as the in-depth guide to Joining and Splitting lists in Guava.


The implementation of all these examples and code snippets can be found in my Guava github project – this is an Eclipse based project, so it should be easy to import and run as it is.

所有这些例子和代码片段的实现可以在我的Guava github项目中找到 – 这是一个基于Eclipse的项目,所以它应该很容易导入和运行,如实。