suggestions applied

kernel/kernel-api/src/main/java/io/delta/kernel/expressions/CollationIdentifier.java → kernel/kernel-api/src/main/java/io/delta/kernel/types/CollationIdentifier.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package io.delta.kernel.expressions;
+package io.delta.kernel.types;
 
 import io.delta.kernel.annotation.Evolving;
 
@@ -22,15 +22,42 @@
 
 import static io.delta.kernel.internal.util.Preconditions.checkArgument;
 
+/**
+ * Identifies collation for string type.
+ * <a href="https://github.com/delta-io/delta/blob/master/protocol_rfcs/collated-string-type.md#collation-identifiers">
+ *   Collation identifiers</a>
+ */
 @Evolving
 public class CollationIdentifier {
+  /**
+   * Spark collation provider.
+   * It provides two collations: {@code UTF8_BINARY} and {@code UTF8_LCASE}.
+   * <br>
+   * {@code UTF8_BINARY} is default string collation. Comparing strings using this collation
+   * is comparing the binary values of their UTF-8 encoded forms.
+   * <br>
+   * The {@code UTF8_LCASE} collation performs case-insensitive comparisons of UTF-8 encoded strings.
+   */
   public static final String PROVIDER_SPARK = "SPARK";
+  /**
+   * ICU collation provider.
+   * <a href="https://unicode-org.github.io/icu/userguide/collation/">ICU library collations</a>
+   */
   public static final String PROVIDER_ICU = "ICU";
 
+  /**
+   * ICU library supported version.
+   */
   public static final String ICU_COLLATOR_VERSION = "75.1";
 
+  /**
+   * Default collation name.
+   */
   public static final String DEFAULT_COLLATION_NAME = "UTF8_BINARY";
 
+  /**
+   * Default collation identifier.
+   */
   public static final CollationIdentifier DEFAULT_COLLATION_IDENTIFIER =
           new CollationIdentifier(PROVIDER_SPARK, DEFAULT_COLLATION_NAME);
 
@@ -39,42 +66,53 @@ public class CollationIdentifier {
   private final Optional<String> version;
 
   public CollationIdentifier(String provider, String collationName) {
+    Objects.requireNonNull(provider, "Collation provider cannot be null.");
+    Objects.requireNonNull(collationName, "Collation name cannot be null.");
+
     this.provider = provider.toUpperCase();
     this.name = collationName.toUpperCase();
     this.version = Optional.empty();
   }
 
-  public CollationIdentifier(String provider, String collationName, Optional<String> version) {
+  public CollationIdentifier(String provider, String collationName, String version) {
     Objects.requireNonNull(provider, "Collation provider cannot be null.");
     Objects.requireNonNull(collationName, "Collation name cannot be null.");
     Objects.requireNonNull(version, "Provider version cannot be null.");
 
     this.provider = provider.toUpperCase();
     this.name = collationName.toUpperCase();
-    if (version.isPresent()) {
-      this.version = Optional.of(version.get().toUpperCase());
-    } else {
-      this.version = Optional.empty();
-    }
-  }
-
-  public String toStringWithoutVersion() {
-    return String.format("%s.%s", provider, name);
+    this.version = Optional.of(version);
   }
 
+  /**
+   *
+   * @return collation provider.
+   */
   public String getProvider() {
     return provider;
   }
 
+  /**
+   *
+   * @return collation name.
+   */
   public String getName() {
     return name;
   }
 
-  // Returns Optional.empty()
+  /**
+   *
+   * @return provider version.
+   */
   public Optional<String> getVersion() {
     return version;
   }
 
+  /**
+   *
+   * @param identifier collation identifier in string form of <br>{@code PROVIDER.COLLATION_NAME[.PROVIDER_VERSION]}.
+   * @return appropriate collation identifier object
+   */
   public static CollationIdentifier fromString(String identifier) {
     long numDots = identifier.chars().filter(ch -> ch == '.').count();
     checkArgument(numDots > 0, String.format("Invalid collation identifier: %s", identifier));
@@ -83,10 +121,13 @@ public static CollationIdentifier fromString(String identifier) {
       return new CollationIdentifier(parts[0], parts[1]);
     } else {
       String[] parts = identifier.split("\\.", 3);
-      return new CollationIdentifier(parts[0], parts[1], Optional.of(parts[2]));
+      return new CollationIdentifier(parts[0], parts[1], parts[2]);
     }
   }
 
+  /**
+   * Collation identifiers are identical when the provider, name, and version are the same.
+   */
   @Override
   public boolean equals(Object o) {
     if (!(o instanceof CollationIdentifier)) {
@@ -99,6 +140,18 @@ public boolean equals(Object o) {
             && this.version.equals(other.version);
   }
 
+  /**
+   *
+   * @return collation identifier in form of {@code PROVIDER.COLLATION_NAME}.
+   */
+  public String toStringWithoutVersion() {
+    return String.format("%s.%s", provider, name);
+  }
+
+  /**
+   *
+   * @return collation identifier in form of {@code PROVIDER.COLLATION_NAME[.PROVIDER_VERSION]}
+   */
   @Override
   public String toString() {
     if (version.isPresent()) {

kernel/kernel-api/src/main/java/io/delta/kernel/types/StringType.java

@@ -16,7 +16,6 @@
 package io.delta.kernel.types;
 
 import io.delta.kernel.annotation.Evolving;
-import io.delta.kernel.expressions.CollationIdentifier;
 
 /**
  * The data type representing {@code string} type values.

kernel/kernel-api/src/test/scala/io/delta/kernel/expressions/CollationIdentifierSuite.scala → kernel/kernel-api/src/test/scala/io/delta/kernel/types/CollationIdentifierSuite.scala

@@ -13,10 +13,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package io.delta.kernel.expressions
+package io.delta.kernel.types
 
+import io.delta.kernel.types.CollationIdentifier._
 import org.scalatest.funsuite.AnyFunSuite
-import io.delta.kernel.expressions.CollationIdentifier._
 
 import java.util.Optional