szetszwo commented on code in PR #10919:
URL: https://github.com/apache/ozone/pull/10919#discussion_r3699709691
##########
hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/CompositeKey.java:
##########
@@ -18,53 +18,94 @@
package org.apache.hadoop.hdds.utils;
import java.util.Arrays;
+import java.util.Objects;
+import org.apache.ratis.util.Preconditions;
/**
* This is a utility to combine multiple objects as a key that can be used in
* hash map access. The advantage of this is that it is cheap in comparison
* to other methods like string concatenation.
- *
- * For example, if a composition of volume, bucket and key is needed to
- * access a hash map, the natural method is:
- * <pre> {@code
- * String key = "/" + volume + "/" + bucket + "/" + key.
- * map.put(key, value);
- * }</pre>
- * This is costly because it creates (and stores) a new buffer.
- *
- * In comparison, the following achieve the same logic without creating any new
- * buffer.
- * <pre> {@code
- * Object key = combineKeys(volume, bucket, key).
- * map.put(key, value);
- * }</pre>
- *
*/
-public final class CompositeKey {
- private final int hashCode;
- private final Object[] components;
-
- CompositeKey(Object[] components) {
- this.components = components;
- this.hashCode = Arrays.hashCode(components);
+public abstract class CompositeKey {
+ /** The same as {@link Arrays#hashCode(Object[])} for one loop step. */
+ static int hash(int result, Object next) {
+ return 31 * result + next.hashCode();
}
- @Override
- public int hashCode() {
- return hashCode;
+ private static final class TwoComponents extends CompositeKey {
+ private final int hashCode;
+ private final Object first;
+ private final Object second;
+
+ private TwoComponents(Object first, Object second) {
+ this.hashCode = hash(hash(1, first), second);
Review Comment:
@spacemonkd , It would be easier to understand if you could quote also line
42 and 43.
Or, if you showed below instead.
```diff
+++
b/hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/CompositeKey.java
@@ -38,9 +38,9 @@ private static final class TwoComponents extends
CompositeKey {
private final Object second;
private TwoComponents(Object first, Object second) {
- this.hashCode = hash(hash(1, first), second);
this.first = Objects.requireNonNull(first, "first == null");
this.second = Objects.requireNonNull(second, "second == null");
+ this.hashCode = hash(hash(1, first), second);
}
```
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