desruisseaux commented on code in PR #1378:
URL: https://github.com/apache/maven/pull/1378#discussion_r1455178371
##########
api/maven-api-core/src/main/java/org/apache/maven/api/DependencyProperties.java:
##########
@@ -33,27 +36,226 @@
@Immutable
public interface DependencyProperties {
/**
- * Boolean flag telling that dependency contains all of its dependencies.
Value of this key should be parsed with
- * {@link Boolean#parseBoolean(String)} to obtain value.
+ * Keys in the dependency properties map.
+ * Each key can be associated to values of a specific class.
+ *
+ * @param <V> type of value associated to the key
+ */
+ class Key<V> {
+ /**
+ * The keys that are defined in this {@code DependencyProperties} map.
+ * Accesses to this map shall be synchronized on the map.
+ *
+ * @see #intern()
+ */
+ private static final Map<String, Key<?>> INTERNS = new HashMap<>();
+
+ /**
+ * Value returned by {@link #name()}.
+ */
+ @Nonnull
+ private final String name;
+
+ /**
+ * Value returned by {@link #valueType()}.
+ */
+ @Nonnull
+ private final Class<V> valueType;
+
+ /**
+ * Creates a new key.
+ *
+ * @param name name of the key
+ * @param valueType type of value associated to the key
+ */
+ public Key(@Nonnull final String name, @Nonnull final Class<V>
valueType) {
+ this.name = Objects.requireNonNull(name);
+ this.valueType = Objects.requireNonNull(valueType);
+ }
+
+ /**
+ * If a key exists in the {@linkplain #intern() intern pool} for the
given name, returns that key.
+ * Otherwise, if the {@code defaultType} is non-null, creates a key
for values of the specified type.
+ * Otherwise, returns {@code null}.
+ *
+ * @param name name of the key to search or create
+ * @param defaultType value type of the key to create if none exist
for the given name, or {@code null}
+ * @return key found or created, or {@code null} if no key was found
and {@code defaultType} is null
+ *
+ * @see #intern()
+ */
+ public static Key<?> forName(String name, Class<?> defaultType) {
+ Key<?> key;
+ synchronized (INTERNS) {
+ key = INTERNS.get(name);
+ }
+ if (key == null && defaultType != null) {
+ key = new Key<>(name, defaultType);
+ }
+ return key;
+ }
+
+ /**
+ * {@return the name of the key}.
+ */
+ @Nonnull
+ public String name() {
+ return name;
+ }
+
+ /**
+ * {@return the type of value associated to the key}.
+ */
+ @Nonnull
+ public Class<V> valueType() {
+ return valueType;
+ }
+
+ /**
+ * {@return a canonical representation of this key}. A pool of keys,
initially empty, is maintained privately.
+ * When the {@code intern()} method is invoked, if the pool already
contains a key equal to this {@code Key}
+ * as determined by the {@link #equals(Object)} method, then the key
from the pool is returned. Otherwise,
+ * if no key exist in the pool for this key {@linkplain #name() name},
then this {@code Key} object is added
+ * to the pool and {@code this} is returned. Otherwise an {@link
IllegalStateException} is thrown.
+ *
+ * @throws IllegalStateException if a key exists in the pool for the
same name but a different class of values.
+ *
+ * @see String#intern()
+ */
+ @SuppressWarnings("unchecked")
+ public Key<V> intern() {
+ Key<?> previous;
+ synchronized (INTERNS) {
+ previous = INTERNS.putIfAbsent(name, this);
+ }
+ if (previous == null) {
+ return this;
+ }
+ if (equals(previous)) {
+ return (Key<V>) previous;
+ }
+ throw new IllegalStateException("Key " + name + " already exists
for a different class of values.");
+ }
+
+ /**
+ * {@return a string representation of this key}.
+ * By default, this is the name of this key.
+ */
+ @Override
+ public String toString() {
+ return name;
+ }
+
+ /**
+ * {@return an hash code value for this key}.
+ */
+ @Override
+ public int hashCode() {
+ return 7 + name.hashCode() + 31 * valueType.hashCode();
Review Comment:
No objection, but `name` and `valueType` cannot be null and the current code
avoids implicit creation of a temporary array. But I agree that the performance
impact is probably unnoticeable.
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