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At a glance

1. 1ImmutableList.of(1, 2, 3), ImmutableMap.of("a", 1), ImmutableSet.copyOf(x): immutable, null-hostile collections that fail fast on a null elementThe JDK now has List.of and List.copyOf too.
2. 2Multimap<K, V> is a map from a key to several values: ArrayListMultimap.create().put("fruit", "apple") replaces Map<K, List<V>> with computeIfAbsentBiMap keeps keys and values unique both ways, Table is a map with two keys, Multiset counts occurrences.
3. 3Joiner.on(", ").skipNulls().join(list) and Splitter.on(',').trimResults().omitEmptyStrings().split(text) handle the edge cases String.join and split do not
4. 4Preconditions.checkArgument(x > 0, "x must be positive but was %s", x) validates argumentsCacheBuilder.newBuilder().maximumSize(1000).expireAfterWrite(10, MINUTES).build(loader) builds a loading cache.

• Guava is a big, widely used dependency; versions clash on the class path (an old Guava from another library wins)
• For new code consider: JDK immutable collections and streams for the basics, and Caffeine instead of the Guava cache (the successor with better performance)
• ImmutableList has specialised implementations (empty, single element, regular array) and is a true immutable copy, not a wrapper, so there is no way to change it through another reference

import com.google.common.base.*;import com.google.common.collect.*;import java.util.List;public class Menu {  static final ImmutableList<String> DAYS = ImmutableList.of("mon", "tue", "wed");  static String line(List<String> items) { return Joiner.on(", ").skipNulls().join(items); }  static Iterable<String> parts(String csv) { return Splitter.on(',').trimResults().omitEmptyStrings().split(csv); }  static Multimap<String, String> group() {    Multimap<String, String> m = ArrayListMultimap.create();    m.put("fruit", "apple"); m.put("fruit", "pear");    return m;  }  static void check(int n) { Preconditions.checkArgument(n > 0, "n must be positive but was %s", n); }}

1. line 5 uses ImmutableList, the core of Guava utilities
2. line 6 uses Joiner, the core of Guava utilities
3. line 7 uses Splitter, the core of Guava utilities
4. line 8 uses Multimap, the core of Guava utilities
5. line 9 uses Multimap, the core of Guava utilities
6. line 13 uses Preconditions, the core of Guava utilities

How Unravel recognises it

When you paste code, Unravel looks for these signs of guava utilities. Spotting them yourself is a good habit when you read unfamiliar code:

• Types: ImmutableList ImmutableMap ImmutableSet Lists Maps Sets Joiner Splitter Preconditions Multimap ArrayListMultimap CacheBuilder LoadingCache Stopwatch and 11 more

Part of a learning path

• JDBC and everyday libraries · previous: ResultSet and mapping rows to objects · next: Apache Commons helpers

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