address comments

core/src/main/java/org/apache/iceberg/NaNFieldMetrics.java → core/src/main/java/org/apache/iceberg/FloatFieldMetrics.java

@@ -28,39 +28,35 @@
  * This wrapper ensures that metrics not being updated by those writers will not be incorrectly used, by throwing
  * exceptions when they are accessed.
  */
-public class NaNFieldMetrics extends FieldMetrics {
+public class FloatFieldMetrics extends FieldMetrics {
 
   /**
    * Constructor for creating a FieldMetrics with only NaN counter.
    * @param id field id being tracked by the writer
    * @param nanValueCount number of NaN values, will only be non-0 for double or float field.
    */
-  public NaNFieldMetrics(int id,
-                         long nanValueCount) {
+  public FloatFieldMetrics(int id,
+                           long nanValueCount) {
     super(id, 0L, 0L, nanValueCount, null, null);
   }
 
   @Override
   public long valueCount() {
-    throw new IllegalStateException(
-        "Shouldn't access valueCount() within NaNOnlyFieldMetrics, as this metric is tracked in file statistics. ");
+    throw new IllegalStateException("Shouldn't access this method, as this metric is tracked in file statistics. ");
   }
 
   @Override
   public long nullValueCount() {
-    throw new IllegalStateException(
-        "Shouldn't access nullValueCount() within NaNOnlyFieldMetrics, as this metric is tracked in file statistics. ");
+    throw new IllegalStateException("Shouldn't access this method, as this metric is tracked in file statistics. ");
   }
 
   @Override
   public ByteBuffer lowerBound() {
-    throw new IllegalStateException(
-        "Shouldn't access lowerBound() within NaNOnlyFieldMetrics, as this metric is tracked in file statistics. ");
+    throw new IllegalStateException("Shouldn't access this method, as this metric is tracked in file statistics. ");
   }
 
   @Override
   public ByteBuffer upperBound() {
-    throw new IllegalStateException(
-        "Shouldn't access upperBound() within NaNOnlyFieldMetrics, as this metric is tracked in file statistics. ");
+    throw new IllegalStateException("Shouldn't access this method, as this metric is tracked in file statistics. ");
   }
 }

core/src/main/java/org/apache/iceberg/MetricsUtil.java

@@ -22,15 +22,21 @@
 import java.util.Map;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
 import org.apache.iceberg.relocated.com.google.common.collect.Maps;
 
 public class MetricsUtil {
 
   private MetricsUtil() {
   }
 
+  /**
+   * Construct mapping relationship between column id to NaN value counts from input metrics and metrics config.
+   */
   public static Map<Integer, Long> createNanValueCounts(
       Stream<FieldMetrics> fieldMetrics, MetricsConfig metricsConfig, Schema inputSchema) {
+    Preconditions.checkNotNull(metricsConfig, "metricsConfig is required");
+
     if (fieldMetrics == null || inputSchema == null) {
       return Maps.newHashMap();
     }
@@ -40,7 +46,13 @@ public static Map<Integer, Long> createNanValueCounts(
         .collect(Collectors.toMap(FieldMetrics::id, FieldMetrics::nanValueCount));
   }
 
+  /**
+   * Extract MetricsMode for the given field id from metrics config.
+   */
   public static MetricsModes.MetricsMode metricsMode(Schema inputSchema, MetricsConfig metricsConfig, int fieldId) {
+    Preconditions.checkNotNull(inputSchema, "inputSchema is required");
+    Preconditions.checkNotNull(metricsConfig, "metricsConfig is required");
+
     String columnName = inputSchema.findColumnName(fieldId);
     return metricsConfig.columnMode(columnName);
   }

parquet/src/main/java/org/apache/iceberg/parquet/ParquetValueWriters.java

@@ -31,7 +31,7 @@
 import java.util.stream.Stream;
 import org.apache.avro.util.Utf8;
 import org.apache.iceberg.FieldMetrics;
-import org.apache.iceberg.NaNFieldMetrics;
+import org.apache.iceberg.FloatFieldMetrics;
 import org.apache.iceberg.deletes.PositionDelete;
 import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
 import org.apache.iceberg.relocated.com.google.common.collect.ImmutableList;
@@ -189,7 +189,7 @@ public void write(int repetitionLevel, Float value) {
 
     @Override
     public Stream<FieldMetrics> metrics() {
-      return Stream.of(new NaNFieldMetrics(id, nanCount));
+      return Stream.of(new FloatFieldMetrics(id, nanCount));
     }
   }
 
@@ -213,7 +213,7 @@ public void write(int repetitionLevel, Double value) {
 
     @Override
     public Stream<FieldMetrics> metrics() {
-      return Stream.of(new NaNFieldMetrics(id, nanCount));
+      return Stream.of(new FloatFieldMetrics(id, nanCount));
     }
   }