Add orThrow and orDefault methods to Index

api/src/main/java/net/kyori/adventure/util/Index.java

@@ -29,9 +29,12 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.NoSuchElementException;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.function.IntFunction;
+
+import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -154,6 +157,37 @@ private Index(final Map<K, V> keyToValue, final Map<V, K> valueToKey) {
     return this.valueToKey.get(value);
   }
 
+  /**
+   * Gets the key for a value or throws an exception.
+   *
+   * @param value the value
+   * @return the key
+   * @throws NoSuchElementException if there is no key for the value
+   * @since 4.11.0
+   */
+  public @NotNull K keyOrThrow(final @NotNull V value) {
+    final K key = this.key(value);
+    if (key == null) {
+      throw new NoSuchElementException("There is no key for value " + value);
+    }
+    return key;
+  }
+
+  /**
+   * Gets a key by its value or returns
+   * a fallback key.
+   *
+   * @param value the value
+   * @param defaultKey the fallback key
+   * @return the key
+   * @since 4.11.0
+   */
+  @Contract("_, null -> null; _, !null -> !null")
+  public K keyOrDefault(final @NotNull V value, @Nullable K defaultKey) {
+    final K key = this.key(value);
+    return key == null ? defaultKey : key;
+  }
+
   /**
    * Gets the keys.
    *
@@ -175,6 +209,37 @@ private Index(final Map<K, V> keyToValue, final Map<V, K> valueToKey) {
     return this.keyToValue.get(key);
   }
 
+  /**
+   * Gets a value by its key.
+   *
+   * @param key the key
+   * @return the value
+   * @throws NoSuchElementException if there is no value for the key
+   * @since 4.11.0
+   */
+  public @NotNull V valueOrThrow(final @NotNull K key) {
+    final V value = this.value(key);
+    if (value == null) {
+      throw new NoSuchElementException("There is no value for key " + key);
+    }
+    return value;
+  }
+
+  /**
+   * Gets a value by its key or returns
+   * a fallback value.
+   *
+   * @param key the key
+   * @param defaultValue the fallback value
+   * @return the value
+   * @since 4.11.0
+   */
+  @Contract("_, null -> null; _, !null -> !null")
+  public V valueOrDefault(final @NotNull K key, @Nullable V defaultValue) {
+    final V value = this.value(key);
+    return value == null ? defaultValue : value;
+  }
+
   /**
    * Get an unmodifiable mapping of index entries from key to value.
    *

api/src/test/java/net/kyori/adventure/util/IndexTest.java

@@ -23,6 +23,7 @@
  */
 package net.kyori.adventure.util;
 
+import java.util.NoSuchElementException;
 import java.util.UUID;
 import org.junit.jupiter.api.Test;
 
@@ -31,7 +32,7 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 class IndexTest {
-  private static final Index<String, Thing> THINGS = Index.create(Thing.class, thing -> thing.name);
+  private static final Index<String, Thing> THINGS = Index.create(Thing.class, thing -> thing.name, Thing.ABC, Thing.DEF);
 
   @Test
   void testCreateWithNonUniqueKey() {
@@ -46,17 +47,39 @@ void testCreateWithNonUniqueValue() {
   @Test
   void testKey() {
     for (final Thing thing : Thing.values()) {
+      if (thing == Thing.NOT_PRESENT) continue;
       assertEquals(thing.name, THINGS.key(thing));
     }
   }
 
   @Test
   void testValue() {
     for (final Thing thing : Thing.values()) {
+      if (thing == Thing.NOT_PRESENT) continue;
       assertEquals(thing, THINGS.value(thing.name));
     }
   }
 
+  @Test
+  void testValueOrThrow() {
+    assertThrows(NoSuchElementException.class, () -> THINGS.valueOrThrow("__NO_VALUE__"));
+  }
+
+  @Test
+  void testKeyOrThrow() {
+    assertThrows(NoSuchElementException.class, () -> THINGS.keyOrThrow(Thing.NOT_PRESENT));
+  }
+
+  @Test
+  void testValueOrDefault() {
+    assertEquals(Thing.NOT_PRESENT, THINGS.valueOrDefault("__NO_VALUE__", Thing.NOT_PRESENT));
+  }
+
+  @Test
+  void testKeyOrDefault() {
+    assertEquals("__DEFAULT__", THINGS.keyOrDefault(Thing.NOT_PRESENT, "__DEFAULT__"));
+  }
+
   @Test
   void testKeys() {
     assertThat(THINGS.keys()).containsExactly("abc", "def");
@@ -69,7 +92,8 @@ void testValues() {
 
   private enum Thing {
     ABC("abc"),
-    DEF("def");
+    DEF("def"),
+    NOT_PRESENT("not_present");
 
     private final String name;