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# API Completeness
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Framework for verifying API parity between Java and Scala implementations using reflection-based method comparison. Essential for ensuring consistent API coverage across language bindings.
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## Core Base Classes
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### ScalaAPICompletenessTestBase
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Abstract base class providing infrastructure for comparing Java and Scala API implementations using reflection.
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```java { .api }
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public abstract class ScalaAPICompletenessTestBase {
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    protected static final Logger LOG = LoggerFactory.getLogger(ScalaAPICompletenessTestBase.class);
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    // Core comparison methods
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    protected void compareApis(Class<?> javaClass, Class<?> scalaClass);
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    protected void compareApis(Class<?> javaClass, Class<?> scalaClass, Set<String> excludedMethods);
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    // Method filtering and exclusion
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    protected boolean isExcluded(Method method);
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    protected boolean isExcluded(String methodName);
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    protected Set<String> getExcludedMethods();
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    // Comparison utilities
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    protected boolean methodsMatch(Method javaMethod, Method scalaMethod);
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    protected String getMethodSignature(Method method);
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    protected void reportMissingMethods(Set<String> missingMethods, String apiType);
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}
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```
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### TupleComparatorTestBase
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Abstract base class for testing tuple comparator implementations between Java and Scala.
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```java { .api }
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public abstract class TupleComparatorTestBase<T> {
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    protected TypeComparator<T> javaComparator;
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    protected TypeComparator<T> scalaComparator;
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    @Before
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    public abstract void setup();
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    // Comparison testing methods
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    protected void testComparatorEquality(T value1, T value2);
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    protected void testComparatorSerialization();
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    protected void testComparatorNormalization();
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    // Utility methods
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    protected abstract T[] getTestData();
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    protected abstract TypeComparator<T> createJavaComparator();
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    protected abstract TypeComparator<T> createScalaComparator();
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}
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```
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### PairComparatorTestBase
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Abstract base class for testing pair comparator implementations.
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```java { .api }
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public abstract class PairComparatorTestBase<T1, T2> {
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    protected TypePairComparator<T1, T2> javaPairComparator;
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    protected TypePairComparator<T1, T2> scalaPairComparator;
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    @Before  
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    public abstract void setup();
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    // Pair comparison testing
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    protected void testPairComparatorEquality(T1 first1, T2 second1, T1 first2, T2 second2);
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    protected void testPairComparatorSerialization();
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    // Abstract methods for test data
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    protected abstract T1[] getFirstTypeTestData();
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    protected abstract T2[] getSecondTypeTestData();
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    protected abstract TypePairComparator<T1, T2> createJavaPairComparator();
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    protected abstract TypePairComparator<T1, T2> createScalaPairComparator();
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}
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```
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## API Comparison Utilities
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### MethodSignatureComparator
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Utility for comparing method signatures between Java and Scala implementations.
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```java { .api }
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public class MethodSignatureComparator {
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    public static boolean signaturesMatch(Method javaMethod, Method scalaMethod);
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    public static String normalizeSignature(Method method);
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    public static boolean returnTypesCompatible(Class<?> javaReturn, Class<?> scalaReturn);
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    public static boolean parametersCompatible(Class<?>[] javaParams, Class<?>[] scalaParams);
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}
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```
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### ReflectionTestUtils
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Utilities for reflection-based testing and method analysis.
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```java { .api }
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public class ReflectionTestUtils {
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    public static Set<Method> getPublicMethods(Class<?> clazz);
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    public static Set<Method> getPublicMethods(Class<?> clazz, Set<String> excludedNames);
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    public static boolean isMethodExcluded(Method method, Set<String> exclusions);
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    public static String getSimpleMethodSignature(Method method);
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}
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```
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## Usage Examples
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### Basic API Completeness Test
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```java
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public class DataSetAPICompletenessTest extends ScalaAPICompletenessTestBase {
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    @Test
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    public void testDataSetAPI() {
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        Class<?> javaDataSet = org.apache.flink.api.java.DataSet.class;
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        Class<?> scalaDataSet = org.apache.flink.api.scala.DataSet.class;
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        // Compare APIs with standard exclusions
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        compareApis(javaDataSet, scalaDataSet);
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    }
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    @Override
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    protected Set<String> getExcludedMethods() {
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        Set<String> excluded = new HashSet<>();
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        // Exclude Scala-specific methods
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        excluded.add("$plus$plus"); // Scala ++ operator
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        excluded.add("$colon$colon"); // Scala :: operator
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        // Exclude internal methods
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        excluded.add("clean");
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        excluded.add("getExecutionEnvironment");
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        return excluded;
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    }
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    @Override
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    protected boolean isExcluded(Method method) {
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        // Additional custom exclusion logic
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        String methodName = method.getName();
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        // Exclude synthetic methods
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        if (method.isSynthetic()) {
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            return true;
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        }
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        // Exclude bridge methods
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        if (method.isBridge()) {
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            return true;
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        }
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        // Exclude Scala-specific naming patterns
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        if (methodName.contains("$")) {
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            return true;
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        }
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        return super.isExcluded(method);
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    }
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}
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```
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### Tuple Comparator Testing
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```java
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public class Tuple2ComparatorTest extends TupleComparatorTestBase<Tuple2<String, Integer>> {
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    @Override
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    public void setup() {
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        javaComparator = createJavaComparator();
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        scalaComparator = createScalaComparator();
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    }
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    @Test
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    public void testTuple2Comparison() {
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        Tuple2<String, Integer> tuple1 = new Tuple2<>("hello", 42);
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        Tuple2<String, Integer> tuple2 = new Tuple2<>("world", 24);
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        testComparatorEquality(tuple1, tuple2);
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        testComparatorSerialization();
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        testComparatorNormalization();
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    }
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    @Override
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    protected Tuple2<String, Integer>[] getTestData() {
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        return new Tuple2[]{
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            new Tuple2<>("a", 1),
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            new Tuple2<>("b", 2),
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            new Tuple2<>("c", 3),
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            new Tuple2<>("a", 1), // Duplicate for equality testing
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        };
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    }
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    @Override
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    protected TypeComparator<Tuple2<String, Integer>> createJavaComparator() {
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        return new TupleComparator<>(
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            new int[]{0, 1}, // Key positions
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            new TypeComparator[]{
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                new StringComparator(true),
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                new IntComparator(true)
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            },
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            new TypeSerializer[]{
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                StringSerializer.INSTANCE,
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                IntSerializer.INSTANCE
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            }
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        );
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    }
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    @Override
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    protected TypeComparator<Tuple2<String, Integer>> createScalaComparator() {
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        // Create Scala equivalent comparator
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        return new ScalaTupleComparator<>(
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            new int[]{0, 1},
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            new TypeComparator[]{
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                new StringComparator(true),
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                new IntComparator(true) 
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            }
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        );
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    }
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}
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```
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### Custom API Comparison with Detailed Reporting
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```java
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public class CustomAPICompletenessTest extends ScalaAPICompletenessTestBase {
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    @Test
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    public void testStreamingAPICompleteness() {
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        Class<?> javaDataStream = org.apache.flink.streaming.api.datastream.DataStream.class;
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        Class<?> scalaDataStream = org.apache.flink.streaming.api.scala.DataStream.class;
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        Set<String> customExclusions = new HashSet<>();
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        customExclusions.add("javaStream"); // Scala-specific bridge method
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        customExclusions.add("scalaStream"); // Java-specific bridge method
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        compareApis(javaDataStream, scalaDataStream, customExclusions);
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    }
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    @Override
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    protected void compareApis(Class<?> javaClass, Class<?> scalaClass, Set<String> excludedMethods) {
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        LOG.info("Comparing {} with {}", javaClass.getSimpleName(), scalaClass.getSimpleName());
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        Set<Method> javaMethods = getFilteredMethods(javaClass, excludedMethods);
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        Set<Method> scalaMethods = getFilteredMethods(scalaClass, excludedMethods);
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        // Find methods in Java but not in Scala
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        Set<String> javaSignatures = javaMethods.stream()
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            .map(this::getMethodSignature)
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            .collect(Collectors.toSet());
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        Set<String> scalaSignatures = scalaMethods.stream()
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            .map(this::getMethodSignature)
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            .collect(Collectors.toSet());
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        Set<String> missingInScala = new HashSet<>(javaSignatures);
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        missingInScala.removeAll(scalaSignatures);
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        Set<String> missingInJava = new HashSet<>(scalaSignatures);
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        missingInJava.removeAll(javaSignatures);
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        // Report findings
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        if (!missingInScala.isEmpty()) {
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            reportMissingMethods(missingInScala, "Scala API");
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        }
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        if (!missingInJava.isEmpty()) {
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            reportMissingMethods(missingInJava, "Java API");
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        }
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        // Assertions
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        assertTrue("Scala API missing methods: " + missingInScala, missingInScala.isEmpty());
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        assertTrue("Java API has extra methods: " + missingInJava, missingInJava.isEmpty());
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        LOG.info("API comparison successful: {} methods verified", javaSignatures.size());
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    }
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    private Set<Method> getFilteredMethods(Class<?> clazz, Set<String> excludedMethods) {
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        return ReflectionTestUtils.getPublicMethods(clazz, excludedMethods);
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    }
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}
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```
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### Comprehensive Operator API Testing
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```java  
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public class OperatorAPICompletenessTest extends ScalaAPICompletenessTestBase {
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    @Test
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    public void testAllOperatorAPIs() {
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        // Test core transformation operators
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        testOperatorAPI("DataSet", 
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            org.apache.flink.api.java.DataSet.class,
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            org.apache.flink.api.scala.DataSet.class);
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        testOperatorAPI("DataStream",
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            org.apache.flink.streaming.api.datastream.DataStream.class,
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            org.apache.flink.streaming.api.scala.DataStream.class);
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        testOperatorAPI("KeyedStream",
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            org.apache.flink.streaming.api.datastream.KeyedStream.class,
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            org.apache.flink.streaming.api.scala.KeyedStream.class);
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    }
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    private void testOperatorAPI(String apiName, Class<?> javaClass, Class<?> scalaClass) {
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        LOG.info("Testing {} API completeness", apiName);
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        try {
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            compareApis(javaClass, scalaClass);
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            LOG.info("{} API comparison successful", apiName);
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        } catch (AssertionError e) {
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            LOG.error("{} API comparison failed: {}", apiName, e.getMessage());
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            throw new AssertionError(apiName + " API completeness test failed", e);
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        }
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    }
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    @Override
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    protected Set<String> getExcludedMethods() {
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        Set<String> excluded = super.getExcludedMethods();
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        // Common exclusions across all operator APIs
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        excluded.add("returns"); // Type hint methods
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        excluded.add("getType");
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        excluded.add("getTransformation");
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        // Scala collection interop methods
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        excluded.add("asScala");
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        excluded.add("asJava");
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        return excluded;
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    }
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}
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```
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### Serialization Compatibility Testing
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```java
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public class SerializationAPICompletenessTest extends ScalaAPICompletenessTestBase {
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    @Test
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    public void testSerializerAPIs() {
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        compareSerializerAPIs(
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            "Tuple2Serializer",
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            org.apache.flink.api.common.typeutils.base.TupleSerializer.class,
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            org.apache.flink.api.scala.typeutils.ScalaTupleSerializer.class
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        );
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    }
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    private void compareSerializerAPIs(String serializerName, Class<?> javaClass, Class<?> scalaClass) {
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        LOG.info("Comparing {} implementations", serializerName);
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        // Get serialization-specific methods
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        Set<Method> javaMethods = Arrays.stream(javaClass.getMethods())
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            .filter(m -> isSerializationMethod(m))
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            .collect(Collectors.toSet());
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        Set<Method> scalaMethods = Arrays.stream(scalaClass.getMethods())
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            .filter(m -> isSerializationMethod(m))
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            .collect(Collectors.toSet());
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        // Compare method signatures
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        compareMethodSets(javaMethods, scalaMethods, serializerName);
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    }
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    private boolean isSerializationMethod(Method method) {
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        String name = method.getName();
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        return name.equals("serialize") || 
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               name.equals("deserialize") ||
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               name.equals("getLength") ||
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               name.equals("copy");
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    }
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    private void compareMethodSets(Set<Method> javaMethods, Set<Method> scalaMethods, String context) {
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        Set<String> javaSignatures = javaMethods.stream()
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            .map(this::getMethodSignature)
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            .collect(Collectors.toSet());
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        Set<String> scalaSignatures = scalaMethods.stream()
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            .map(this::getMethodSignature)
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            .collect(Collectors.toSet());
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        assertEquals(context + " method signatures should match", javaSignatures, scalaSignatures);
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    }
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}