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

*** 33,42 ****
--- 33,43 ----
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
+ import java.util.Objects;
  import java.util.Set;
  
  /**
   * The result of hashing the contents of a number of module artifacts.
   */
*** 48,58 ****
       */
      public static interface HashSupplier {
          byte[] generate(String algorithm);
      }
  
- 
      private final String algorithm;
      private final Map<String, byte[]> nameToHash;
  
      /**
       * Creates a {@code ModuleHashes}.
--- 49,58 ----
*** 140,145 ****
--- 140,180 ----
              Path path = entry.getValue();
              nameToHash.put(name, computeHash(path, algorithm));
          }
          return new ModuleHashes(algorithm, nameToHash);
      }
+ 
+     /**
+      * This is used by jdk.internal.module.SystemModules class
+      * generated at link time.
+      */
+     public static class Builder {
+         final String algorithm;
+         Map<String, byte[]> nameToHash;
+ 
+         Builder(String algorithm) {
+             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) {
+                 return new ModuleHashes(algorithm, nameToHash);
+             } else {
+                 return null;
+             }
+         }
+     }
  }