1. Overview
1.概述
In this tutorial, we’ll show how to use the Google Guava’s Table interface and its multiple implementations.
在本教程中，我们将展示如何使用Google Guava的Table接口及其多种实现。
Guava’s Table is a collection that represents a table like structure containing rows, columns and the associated cell values. The row and the column act as an ordered pair of keys.
Guava的Table是一个集合，表示一个类似于表格的结构，包含行、列和相关的单元格值。行和列作为一对有序的键。
2. Google Guava’s Table
2.Google Guava的Table
Let’s have a look at how to use the Table class.
让我们看一下如何使用Table类。
2.1. Maven Dependency
2.1.Maven的依赖性
Let’s start by adding Google’s Guava library dependency in the pom.xml:
让我们先在pom.xml中加入Google的Guava库依赖。
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>31.0.1-jre</version>
</dependency>The latest version of the dependency can be checked here.
最新版本的依赖关系可以在这里查看。
2.2. About
2.2.关于
If we were to represent Guava’s Table using Collections present in core Java, then the structure would be a map of rows where each row contains a map of columns with associated cell values.
如果我们使用核心Java中的Collections来表示Guava的Table，那么这个结构将是一个行的映射，每一行都包含一个带有相关单元格值的列映射。
Table represents a special map where two keys can be specified in combined fashion to refer to a single value.
Table代表了一个特殊的映射，在这个映射中，两个键可以以组合的方式被指定来指代一个单一的值。
It’s similar to creating a map of maps, for example, Map<UniversityName, Map<CoursesOffered, SeatAvailable>>. Table would be also a perfect way of representing the Battleships game board.
这类似于创建一张地图，例如，Map<UniversityName, Map<CoursesOffered, SeatAvailable>>/em>。Table也将是代表战舰游戏板的一种完美方式。
3. Creating
3.创造
You can create an instance of Table in multiple ways:
你可以通过多种方式创建一个Table的实例。
- Using the create method from the class HashBasedTable which uses LinkedHashMap internally:
Table<String, String, Integer> universityCourseSeatTable = HashBasedTable.create(); - If we need a Table whose row keys and the column keys need to be ordered by their natural ordering or by supplying comparators, you can create an instance of a Table using the create method from a class called TreeBasedTable, which uses TreeMap internally:
Table<String, String, Integer> universityCourseSeatTable = TreeBasedTable.create(); - If we know the row keys and the column keys beforehand and the table size is fixed, use the create method from the class ArrayTable:
List<String> universityRowTable = Lists.newArrayList("Mumbai", "Harvard"); List<String> courseColumnTables = Lists.newArrayList("Chemical", "IT", "Electrical"); Table<String, String, Integer> universityCourseSeatTable = ArrayTable.create(universityRowTable, courseColumnTables); - If we intend to create an immutable instance of Table whose internal data are never going to change, use the ImmutableTable class (creating which follows a builder pattern):
Table<String, String, Integer> universityCourseSeatTable = ImmutableTable.<String, String, Integer> builder() .put("Mumbai", "Chemical", 120).build();
4. Using
4.使用
Let’s start with a simple example showing the usage of Table.
让我们从一个简单的例子开始，展示Table的用法。
4.1. Retrieval
4.1.检索
If we know the row key and the column key then we can get the value associated with the row and the column key:
如果我们知道行键和列键，那么我们可以得到与行和列键相关的值。
@Test
public void givenTable_whenGet_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
int seatCount
= universityCourseSeatTable.get("Mumbai", "IT");
Integer seatCountForNoEntry
= universityCourseSeatTable.get("Oxford", "IT");
assertThat(seatCount).isEqualTo(60);
assertThat(seatCountForNoEntry).isEqualTo(null);
}4.2. Checking for an Entry
4.2.检查一个条目
We can check the presence of an entry in a Table based on:
我们可以在Table的基础上检查一个条目的存在。
- Row key
- Column key
- Both row key and column key
- Value
Let’s see how to check for the presence of an entry:
让我们看看如何检查是否存在一个条目。
@Test
public void givenTable_whenContains_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
boolean entryIsPresent
= universityCourseSeatTable.contains("Mumbai", "IT");
boolean courseIsPresent
= universityCourseSeatTable.containsColumn("IT");
boolean universityIsPresent
= universityCourseSeatTable.containsRow("Mumbai");
boolean seatCountIsPresent
= universityCourseSeatTable.containsValue(60);
assertThat(entryIsPresent).isEqualTo(true);
assertThat(courseIsPresent).isEqualTo(true);
assertThat(universityIsPresent).isEqualTo(true);
assertThat(seatCountIsPresent).isEqualTo(true);
}4.3. Removal
4.3.移除
We can remove an entry from the Table by supplying both the row key and column key:
我们可以通过提供行键和列键从Table中删除一个条目。
@Test
public void givenTable_whenRemove_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
int seatCount
= universityCourseSeatTable.remove("Mumbai", "IT");
assertThat(seatCount).isEqualTo(60);
assertThat(universityCourseSeatTable.remove("Mumbai", "IT")).
isEqualTo(null);
}
4.4. Row Key to Cell Value Map
4.4.行键到单元格值图
We can get a Map representation with the key as a row and the value as a CellValue by providing the column key:
我们可以通过提供列键来获得一个Map表示，其中键为行，值为CellValue。
@Test
public void givenTable_whenColumn_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
Map<String, Integer> universitySeatMap
= universityCourseSeatTable.column("IT");
assertThat(universitySeatMap).hasSize(2);
assertThat(universitySeatMap.get("Mumbai")).isEqualTo(60);
assertThat(universitySeatMap.get("Harvard")).isEqualTo(120);
}
4.5. Map Representation of a Table
4.5.表的地图表示法
We can get a Map<UniversityName, Map<CoursesOffered, SeatAvailable>> representation by using the columnMap method:
我们可以通过使用columnMap方法获得Map<UniversityName, Map<CoursesOffered, SeatAvailable>>/em>表示。
@Test
public void givenTable_whenColumnMap_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
Map<String, Map<String, Integer>> courseKeyUniversitySeatMap
= universityCourseSeatTable.columnMap();
assertThat(courseKeyUniversitySeatMap).hasSize(3);
assertThat(courseKeyUniversitySeatMap.get("IT")).hasSize(2);
assertThat(courseKeyUniversitySeatMap.get("Electrical")).hasSize(1);
assertThat(courseKeyUniversitySeatMap.get("Chemical")).hasSize(1);
}
4.6. Column Key to Cell Value Map
4.6.列键到单元格值的映射
We can get a Map representation with the key as a column and the value as a CellValue by providing row key:
我们可以通过提供行键得到一个Map表示法，其中键是一列，值是一个CellValue。
@Test
public void givenTable_whenRow_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
Map<String, Integer> courseSeatMap
= universityCourseSeatTable.row("Mumbai");
assertThat(courseSeatMap).hasSize(2);
assertThat(courseSeatMap.get("IT")).isEqualTo(60);
assertThat(courseSeatMap.get("Chemical")).isEqualTo(120);
}
4.7. Get Distinct Row Key
4.7.获取独特的行键
We can get all the row keys from a table using the rowKeySet method:
我们可以使用rowKeySet方法从一个表中获得所有行键。
@Test
public void givenTable_whenRowKeySet_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
Set<String> universitySet = universityCourseSeatTable.rowKeySet();
assertThat(universitySet).hasSize(2);
}
4.8. Get Distinct Column Key
4.8.获取独特的列键
We can get all column keys from a table using the columnKeySet method:
我们可以使用columnKeySet方法从一个表中获得所有列键。
@Test
public void givenTable_whenColKeySet_returnsSuccessfully() {
Table<String, String, Integer> universityCourseSeatTable
= HashBasedTable.create();
universityCourseSeatTable.put("Mumbai", "Chemical", 120);
universityCourseSeatTable.put("Mumbai", "IT", 60);
universityCourseSeatTable.put("Harvard", "Electrical", 60);
universityCourseSeatTable.put("Harvard", "IT", 120);
Set<String> courseSet = universityCourseSeatTable.columnKeySet();
assertThat(courseSet).hasSize(3);
}
5. Conclusion
5.结论
In this tutorial, we illustrated the methods of the Table class from the Guava library. The Table class provides a collection that represents a table like structure containing rows, columns and associated cell values.
在本教程中，我们说明了Guava库中的Table类的方法。Table类提供了一个集合，代表了一个类似于表格的结构，包含了行、列和相关的单元格值。
The code belonging to the above examples can be found in the GitHub project – this is a Maven-based project, so it should be easy to import and run as is.
属于上述例子的代码可以在GitHub项目中找到–这是一个基于Maven的项目，所以应该很容易导入并按原样运行。