Guava: Google Core Libraries for Java

Guava is available in two flavors:

1. JRE flavor: Requires JDK 1.8 or higher.
2. Android flavor: For Android support or libraries requiring Android compatibility.

Specify the flavor by appending -jre or -android to the version number in your dependency configuration.

### Maven
<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>33.6.0-jre</version>
  <!-- or, for Android: -->
  <version>33.6.0-android</version>
</dependency>

### Gradle
dependencies {
  // Use Guava in your implementation only:
  implementation("com.google.guava:guava:33.6.0-jre")

  // Use Guava types in your public API:
  api("com.google.guava:guava:33.6.0-jre")

  // Android - Use Guava in your implementation only:
  implementation("com.google.guava:guava:33.6.0-android")

  // Android - Use Guava types in your public API:
  api("com.google.guava:guava:33.6.0-android")
}

A StandardTable<R, C, V> is a Table implementation backed by a nested map structure: Map<R, Map<C, V>>. It associates row keys (R) with secondary maps that associate column keys (C) with values (V).

Performance Characteristics

• Row Lookups: Fast. Accessing data by row key is highly efficient because the data is stored in a primary map keyed by R.
• Column Lookups: Slower. Accessing data by column key (e.g., via column(columnKey).get(rowKey)) is still relatively fast because the row key is provided, but operations like column(columnKey).size() require iterating across all row keys.
• Concurrency: This implementation is not synchronized. If multiple threads access the table concurrently and at least one thread modifies it, you must provide external synchronization.

Constraints

• Nulls: Null row keys, column keys, and values are not supported and will result in errors or null returns depending on the method.
• View Limitations: The views returned by column(columnKey), columnKeySet(), and columnMap() return iterators that do not support remove().

The StandardTable provides several ways to view and interact with its data:

• Direct Access: Use get(rowKey, columnKey) to retrieve a specific value.
• Row View: row(rowKey) returns a Map<C, V> representing all columns for that specific row. This map supports mutation (e.g., put, remove, clear).
• Column View: column(columnKey) returns a Map<R, V> representing all rows for that specific column. This view supports mutation, but its iterator does not support remove().
• Cell Set: cellSet() returns a Set<Cell<R, C, V>> containing all mappings. Each Cell is an immutable snapshot of a row/column/value triplet.
• Key Sets:
  • rowKeySet() returns the set of all row keys.
  • columnKeySet() returns the set of all column keys.
• Maps:
  • rowMap() returns a Map<R, Map<C, V>> view.
  • columnMap() returns a Map<C, Map<R, V>> view.

To create a view of a Multimap that only contains entries where the keys satisfy a specific Predicate, use the Multimaps.filterKeys(Multimap, Predicate) method.

This returns a FilteredMultimap, which is a view of the original multimap. Changes to the underlying multimap may be reflected in the filtered view, but attempting to add elements to the filtered view using keys that do not satisfy the predicate will result in an IllegalArgumentException.

// Example usage of Multimaps.filterKeys
Multimap<String, Integer> unfiltered = ArrayListMultimap.create();
unfiltered.put("apple", 1);
unfiltered.put("banana", 2);
unfiltered.put("cherry", 3);

// Filter to only include keys starting with 'a' or 'b'
Multimap<String, Integer> filtered = Multimaps.filterKeys(
    unfiltered, 
    key -> key.startsWith("a") || key.startsWith("b")
);

// filtered contains: {apple=[1], banana=[2]}