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Guava Table 示例教程

2022年07月19日142exmyth

Guava Table 示例教程

本文带你学习Guava Table 接口及其实现。Guava Table 是类似表格结构的集合，包含行、列以及相应的单元格值。行和列作为有序的键。

概述

如果把Guava Table和java核心类中的集合进行比较，则为行map，且每行包含列map，其中有对应的单元格值。Table表示一个特定的map，有两个key以组合的形式引用单个值。类似场景一个map的map，举例：Map<UniversityName, Map<CoursesOffered, SeatAvailable>>。

依赖

maven依赖如下，读者可以查找对应版本：

<dependency> 
    <groupId>com.google.guava</groupId> 
    <artifactId>guava</artifactId> 
    <version>21.0</version> 
</dependency>

创建

有多种方式创建其实例：

  • 使用HashBasedTable 类的create方法，其内部使用LinkedHashMap 类：
Table<String, String, Integer> universityCourseSeatTable  
  = HashBasedTable.create();
  • 如果我们需要Table的行key和列key有序（按自然顺序或提供的比较器排序），可以使用TreeBasedTable的create方法，其内部使用TreeMap：
Table<String, String, Integer> universityCourseSeatTable 
  = TreeBasedTable.create();
  • 如何事先就确定行key和列可以，且table大小固定，可以使用ArrayTable的create方法：
List<String> universityRowTable  
  = Lists.newArrayList("Mumbai", "Harvard"); 
List<String> courseColumnTables  
  = Lists.newArrayList("Chemical", "IT", "Electrical"); 
Table<String, String, Integer> universityCourseSeatTable 
  = ArrayTable.create(universityRowTable, courseColumnTables);
  • 如果需要创建不可变的table实例，其内部数据不能修改，可以使用ImmutableTable 类，使用其builder：
Table<String, String, Integer> universityCourseSeatTable 
  = ImmutableTable.<String, String, Integer> builder() 
  .put("Mumbai", "Chemical", 120).build();

应用

下面通过简单示例说明如何应用Table：

取值

如果确定行key和列key，那么可以通过它们获取关联值：

@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); 
}

检查项是否存在

可以通过下面几种方式检查table的项是否存在：

  • 行key
  • 列key
  • 行key和列key
  • 值

请看示例：

@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); 
}

删除

可以通过行key和列key从table中删除项：

@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); 
}

获取行key和单元格值的映射map

通过列key 获取行key和单元格值的映射map：

@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); 
}

获取table的map表示

通过使用columnMap方法，可以获取 Map<UniversityName, Map<CoursesOffered, SeatAvailable>> 形式的map结构：

@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); 
}

获取列key和单元格值的映射map

通过行key获取列key和单元格值的映射map：

@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); 
}

获取唯一的行key

rowKeySet 方法可以获取所有行key，并自动去重：

@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); 
}

获取唯一的列key

columnKeySet 方法可以获取所有列key，并自动去重：

@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); 
}

总结

本文我们介绍了Guava中Table类及其常用方法。table提供类似表格的结构，包括行、列以及关联值，在实际项目中非常有用。


本文参考链接：https://blog.csdn.net/neweastsun/article/details/84996250
  文章来源：
  https://www.itguest.com/post/ahcb2b1.html
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