apacheGH-44011: [Java] Consider warnings as errors for C Module (apac…

…he#44012)

### Rationale for this change

This PR configs the build such that warnings are considered as errors in the C module. And corresponding code changes have also been made.

### What changes are included in this PR?

Adding flags to consider warnings as errors in javac and fixing the corresponding errors.

### Are these changes tested?

Tested by existing test cases.

### Are there any user-facing changes?

N/A
* GitHub Issue: apache#44011

Authored-by: Vibhatha Lakmal Abeykoon <vibhatha@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>

java/c/pom.xml

@@ -91,5 +91,16 @@ under the License.
         </includes>
       </resource>
     </resources>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <configuration combine.children="append">
+          <compilerArgs>
+            <arg>-Werror</arg>
+          </compilerArgs>
+        </configuration>
+      </plugin>
+    </plugins>
   </build>
 </project>

java/c/src/main/java/org/apache/arrow/c/ArrayExporter.java

@@ -90,7 +90,7 @@ void export(ArrowArray array, FieldVector vector, DictionaryProvider dictionaryP
 
       data.buffers = new ArrayList<>(vector.getExportedCDataBufferCount());
       data.buffers_ptrs =
-          allocator.buffer((long) (vector.getExportedCDataBufferCount()) * Long.BYTES);
+          allocator.buffer((long) vector.getExportedCDataBufferCount() * Long.BYTES);
       vector.exportCDataBuffers(data.buffers, data.buffers_ptrs, NULL);
 
       if (dictionaryEncoding != null) {

java/c/src/main/java/org/apache/arrow/c/BufferImportTypeVisitor.java

@@ -232,7 +232,7 @@ public List<ArrowBuf> visit(ArrowType.Utf8 type) {
   private List<ArrowBuf> visitVariableWidthView(ArrowType type) {
     final int viewBufferIndex = 1;
     final int variadicSizeBufferIndex = this.buffers.length - 1;
-    final long numOfVariadicBuffers = this.buffers.length - 3;
+    final long numOfVariadicBuffers = this.buffers.length - 3L;
     final long variadicSizeBufferCapacity = numOfVariadicBuffers * Long.BYTES;
     List<ArrowBuf> buffers = new ArrayList<>();
 

java/c/src/test/java/org/apache/arrow/c/DictionaryTest.java

@@ -247,8 +247,8 @@ private void createStructVector(StructVector vector) {
 
     // Write the values to child 1
     child1.allocateNew();
-    child1.set(0, "01234567890".getBytes());
-    child1.set(1, "012345678901234567".getBytes());
+    child1.set(0, "01234567890".getBytes(StandardCharsets.UTF_8));
+    child1.set(1, "012345678901234567".getBytes(StandardCharsets.UTF_8));
     vector.setIndexDefined(0);
 
     // Write the values to child 2
@@ -269,8 +269,8 @@ private void createStructVectorInline(StructVector vector) {
 
     // Write the values to child 1
     child1.allocateNew();
-    child1.set(0, "012345678".getBytes());
-    child1.set(1, "01234".getBytes());
+    child1.set(0, "012345678".getBytes(StandardCharsets.UTF_8));
+    child1.set(1, "01234".getBytes(StandardCharsets.UTF_8));
     vector.setIndexDefined(0);
 
     // Write the values to child 2

java/c/src/test/java/org/apache/arrow/c/RoundtripTest.java

@@ -528,14 +528,6 @@ public void testVarBinaryVector() {
     }
   }
 
-  private String generateString(String str, int repetition) {
-    StringBuilder aRepeated = new StringBuilder();
-    for (int i = 0; i < repetition; i++) {
-      aRepeated.append(str);
-    }
-    return aRepeated.toString();
-  }
-
   @Test
   public void testViewVector() {
     // ViewVarCharVector with short strings