make fields final

h2/src/main/org/h2/expression/ExpressionColumn.java

@@ -32,7 +32,7 @@ public class ExpressionColumn extends Expression {
     private final Database database;
     private final String schemaName;
     private final String tableAlias;
-    private String columnName;
+    private final String columnName;
     private ColumnResolver columnResolver;
     private int queryLevel;
     private Column column;

h2/src/main/org/h2/index/SpatialTreeIndex.java

@@ -269,7 +269,7 @@ public class SpatialTreeIndex extends BaseIndex implements SpatialIndex {
         private final Iterator<SpatialKey> it;
         private SpatialKey current;
         private final Table table;
-        private Session session;
+        private final Session session;
 
         public SpatialCursor(Iterator<SpatialKey> it, Table table, Session session) {
             this.it = it;

h2/src/main/org/h2/mvstore/MVMap.java

@@ -41,8 +41,8 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      */
     private final AtomicReference<RootReference> root;
 
-    private int id;
-    private long createVersion;
+    private final int id;
+    private final long createVersion;
     private final DataType keyType;
     private final DataType valueType;
 

h2/src/main/org/h2/table/JoinBatch.java

@@ -1074,8 +1074,8 @@ public final class JoinBatch {
      * Query runner for UNION.
      */
     private static class QueryRunnerUnion extends QueryRunnerBase {
-        Future<Cursor>[] topFutureCursors;
-        private ViewIndexLookupBatchUnion batchUnion;
+        final Future<Cursor>[] topFutureCursors;
+        private final ViewIndexLookupBatchUnion batchUnion;
 
         @SuppressWarnings("unchecked")
         QueryRunnerUnion(ViewIndexLookupBatchUnion batchUnion) {