AVRO-2731: initialize hashmap with good capacity

lang/java/compiler/src/main/velocity/org/apache/avro/compiler/specific/templates/java/classic/record.vm

@@ -837,7 +837,7 @@ $I    }
 $I    long size${nv} = in.readMapStart();
 $I    $t m${nv} = ${var}; // Need fresh name due to limitation of macro system
 $I    if (m${nv} == null) {
-$I      m${nv} = new java.util.HashMap<${kt},${vt}>((int)size${nv});
+$I      m${nv} = new java.util.HashMap<${kt},${vt}>((int)(size${nv} * 4)/3 + 1);
 $I      $var = m${nv};
 $I    } else m${nv}.clear();
 $I    for ( ; 0 < size${nv}; size${nv} = in.mapNext()) {

lang/java/compiler/src/test/java/org/apache/avro/specific/TestGeneratedCode.java

@@ -20,6 +20,8 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.util.HashMap;
+import java.util.Map;
 
 import org.apache.avro.Schema;
 import org.apache.avro.io.Encoder;
@@ -71,8 +73,9 @@ void withoutSchemaMigration() throws IOException {
 
   @Test
   void withSchemaMigration() throws IOException {
+    Map<CharSequence, CharSequence> map = new HashMap<>();
     FullRecordV2 src = new FullRecordV2(true, 731, 87231, 38L, 54.2832F, "Hi there",
-        ByteBuffer.wrap(Utf8.getBytesFor("Hello, world!")));
+        ByteBuffer.wrap(Utf8.getBytesFor("Hello, world!")), map);
     assertTrue(((SpecificRecordBase) src).hasCustomCoders(), "Test schema must allow for custom coders.");
 
     ByteArrayOutputStream out = new ByteArrayOutputStream(1024);

lang/java/compiler/src/test/resources/full_record_v2.avsc

@@ -24,6 +24,7 @@
   }, {
     "name" : "h",
     "type" : "bytes"
-  } ]
+  },
+    { "name" : "myMap", "type" : { "type" : "map", "values" : "string" } }]
 }