src/java.base/share/classes/jdk/internal/module/ModuleHashes.java

rev 16336 : 8171373: Reduce copying during initialization of ModuleHashes
Reviewed-by: alanb, mchung, chegar

@@ -147,32 +147,30 @@
      * This is used by jdk.internal.module.SystemModules class
      * generated at link time.
      */
     public static class Builder {
         final String algorithm;
-        Map<String, byte[]> nameToHash;
+        final Map<String, byte[]> nameToHash;
 
-        Builder(String algorithm) {
+        Builder(String algorithm, int initialCapacity) {
+            this.nameToHash = new HashMap<>(initialCapacity);
             this.algorithm =  Objects.requireNonNull(algorithm);
         }
 
         /**
          * Sets the module hash for the given module name
          */
         public Builder hashForModule(String mn, byte[] hash) {
-            if (nameToHash == null)
-                nameToHash = new HashMap<>();
-
             nameToHash.put(mn, hash);
             return this;
         }
 
         /**
          * Builds a {@code ModuleHashes}.
          */
         public ModuleHashes build() {
-            if (nameToHash != null) {
+            if (!nameToHash.isEmpty()) {
                 return new ModuleHashes(algorithm, nameToHash);
             } else {
                 return null;
             }
         }