refactor: cleans up code / uses java 8 features (#1072)

* chore: refactor c style array declaration

Moves from c style array declaration to java style. E.g. int array[] to
int[] array.

* chore: refactor to use ut8 standard charset

Instead of using the literal String UTF-8

* chore: removes redundant string conversions

* chore: refactor enums

Removes redundant private modifier in enum constructors.
Removes redundant static modifier in inner class enums.

* chore: refactor interfaces

Removes redundant modifiers from interfaces.

* chore: removes unnecessary semicolons

* chore: remove redundant local variable declaration

* chore: removes redundant throws clause

* chore: removes redundant call to close method

* chore: optimise imports

* chore: removes dangling javadoc comment

* chore: removes self-references in javadoc

* chore: refactor long literals

From lower case l to upper case L

* chore: removes octal integers from tests

* chore: simplify arithmetic expressions

* chore: fixes malformed string.format

* chore: removes ignored method call results

* chore: compare strings with equals instead of ==

* chore: simplifies test assertions

* chore: removes redundant calls to string.format

* chore: explicit type argument replaced by <>

* chore: uses try with resources

* chore: replaces if block by switch statement

* chore: uses enhanced for loop

* chore: removes unnecessary boxing

* chore: removes unnecessary unboxing

* chore: refactors to use map.computeIfAbsent

* chore: addresses PR comments

* chore: fixes compilation errors

Author: thiagotnunes

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AbstractReadContext.java

@@ -794,8 +794,7 @@ CloseableIterator<PartialResultSet> startStream(@Nullable ByteString resumeToken
             return stream;
           }
         };
-    GrpcResultSet resultSet = new GrpcResultSet(stream, this);
-    return resultSet;
+    return new GrpcResultSet(stream, this);
   }
 
   private Struct consumeSingleRow(ResultSet resultSet) {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AbstractResultSet.java

@@ -208,7 +208,7 @@ protected com.google.protobuf.Value computeNext() {
       Object merged =
           kind == KindCase.STRING_VALUE
               ? value.getStringValue()
-              : new ArrayList<com.google.protobuf.Value>(value.getListValue().getValuesList());
+              : new ArrayList<>(value.getListValue().getValuesList());
       while (current.getChunkedValue() && pos == current.getValuesCount()) {
         if (!ensureReady(StreamValue.RESULT)) {
           throw newSpannerException(

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncResultSet.java

@@ -39,9 +39,8 @@ enum CursorState {
    * Non-blocking call that attempts to step the cursor to the next position in the stream. The
    * cursor may be inspected only if the cursor returns {@code CursorState.OK}.
    *
-   * <p>A caller will typically call {@link #tryNext()} in a loop inside the ReadyCallback,
-   * consuming all results available. For more information see {@link #setCallback(Executor,
-   * ReadyCallback)}.
+   * <p>A caller will typically call tryNext in a loop inside the ReadyCallback, consuming all
+   * results available. For more information see {@link #setCallback(Executor, ReadyCallback)}.
    *
    * <p>Currently this method may only be called if a ReadyCallback has been registered. This is for
    * safety purposes only, and may be relaxed in future.
@@ -146,8 +145,8 @@ interface ReadyCallback {
    * <ul>
    *   <li>Semi-async: make {@code upstream.emit()} a blocking call. This will block the callback
    *       thread until progress is possible. When coding in this way the threads in the Executor
-   *       provided to {@link #setCallback(Executor, ReadyCallback)} must be blockable without
-   *       causing harm to progress in your system.
+   *       provided to setCallback must be blockable without causing harm to progress in your
+   *       system.
    *   <li>Full-async: call {@code cursor.pause()} and return from the callback with data still in
    *       the Cursor. Once in this state cursor waits until resume() is called before calling
    *       callback again.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncResultSetImpl.java

@@ -62,11 +62,11 @@ private enum State {
     /** Does this state mean that the result set should permanently stop producing rows. */
     private final boolean shouldStop;
 
-    private State() {
+    State() {
       shouldStop = false;
     }
 
-    private State(boolean shouldStop) {
+    State(boolean shouldStop) {
       this.shouldStop = shouldStop;
     }
   }
@@ -116,32 +116,31 @@ private State(boolean shouldStop) {
   private State state = State.INITIALIZED;
 
   /**
-   * {@link #finished} indicates whether all the results from the underlying result set have been
-   * read.
+   * This variable indicates whether all the results from the underlying result set have been read.
    */
   private volatile boolean finished;
 
   private volatile ApiFuture<Void> result;
 
   /**
-   * {@link #cursorReturnedDoneOrException} indicates whether {@link #tryNext()} has returned {@link
-   * CursorState#DONE} or a {@link SpannerException}.
+   * This variable indicates whether {@link #tryNext()} has returned {@link CursorState#DONE} or a
+   * {@link SpannerException}.
    */
   private volatile boolean cursorReturnedDoneOrException;
 
   /**
-   * {@link #pausedLatch} is used to pause the producer when the {@link AsyncResultSet} is paused.
-   * The production of rows that are put into the buffer is only paused once the buffer is full.
+   * This variable is used to pause the producer when the {@link AsyncResultSet} is paused. The
+   * production of rows that are put into the buffer is only paused once the buffer is full.
    */
   private volatile CountDownLatch pausedLatch = new CountDownLatch(1);
   /**
-   * {@link #bufferConsumptionLatch} is used to pause the producer when the buffer is full and the
-   * consumer needs some time to catch up.
+   * This variable is used to pause the producer when the buffer is full and the consumer needs some
+   * time to catch up.
    */
   private volatile CountDownLatch bufferConsumptionLatch = new CountDownLatch(0);
   /**
-   * {@link #consumingLatch} is used to pause the producer when all rows have been put into the
-   * buffer, but the consumer (the callback) has not yet received and processed all rows.
+   * This variable is used to pause the producer when all rows have been put into the buffer, but
+   * the consumer (the callback) has not yet received and processed all rows.
    */
   private volatile CountDownLatch consumingLatch = new CountDownLatch(0);
 
@@ -531,7 +530,7 @@ public <T> ApiFuture<List<T>> toListAsync(
       Preconditions.checkState(
           this.state == State.INITIALIZED, "This AsyncResultSet has already been used.");
       final SettableApiFuture<List<T>> res = SettableApiFuture.<List<T>>create();
-      CreateListCallback<T> callback = new CreateListCallback<T>(res, transformer);
+      CreateListCallback<T> callback = new CreateListCallback<>(res, transformer);
       ApiFuture<Void> finished = setCallback(executor, callback);
       return ApiFutures.transformAsync(
           finished,

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncTransactionManager.java

@@ -49,7 +49,7 @@ public interface AsyncTransactionManager extends AutoCloseable {
    * {@link ApiFuture} that returns a {@link TransactionContext} and that supports chaining of
    * multiple {@link TransactionContextFuture}s to form a transaction.
    */
-  public interface TransactionContextFuture extends ApiFuture<TransactionContext> {
+  interface TransactionContextFuture extends ApiFuture<TransactionContext> {
     /**
      * Sets the first step to execute as part of this transaction after the transaction has started
      * using the specified executor. {@link MoreExecutors#directExecutor()} can be be used for
@@ -65,7 +65,7 @@ <O> AsyncTransactionStep<Void, O> then(
    * is executed using an {@link AsyncTransactionManager}. This future is returned by the call to
    * {@link AsyncTransactionStep#commitAsync()} of the last step in the transaction.
    */
-  public interface CommitTimestampFuture extends ApiFuture<Timestamp> {
+  interface CommitTimestampFuture extends ApiFuture<Timestamp> {
     /**
      * Returns the commit timestamp of the transaction. Getting this value should always be done in
      * order to ensure that the transaction succeeded. If any of the steps in the transaction fails
@@ -125,7 +125,7 @@ Timestamp get(long timeout, TimeUnit unit)
    *         })
    * }</pre>
    */
-  public interface AsyncTransactionStep<I, O> extends ApiFuture<O> {
+  interface AsyncTransactionStep<I, O> extends ApiFuture<O> {
     /**
      * Adds a step to the transaction chain that should be executed using the specified executor.
      * This step is guaranteed to be executed only after the previous step executed successfully.
@@ -150,11 +150,11 @@ <RES> AsyncTransactionStep<O, RES> then(
    * parameters. The method should return an {@link ApiFuture} that will return the result of this
    * step.
    */
-  public interface AsyncTransactionFunction<I, O> {
+  interface AsyncTransactionFunction<I, O> {
     /**
-     * {@link #apply(TransactionContext, Object)} is called when this transaction step is executed.
-     * The input value is the result of the previous step, and this method will only be called if
-     * the previous step executed successfully.
+     * This method is called when this transaction step is executed. The input value is the result
+     * of the previous step, and this method will only be called if the previous step executed
+     * successfully.
      *
      * @param txn the {@link TransactionContext} that can be used to execute statements.
      * @param input the result of the previous transaction step.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncTransactionManagerImpl.java

@@ -79,9 +79,7 @@ public ApiFuture<Void> closeAsync() {
   @Override
   public TransactionContextFutureImpl beginAsync() {
     Preconditions.checkState(txn == null, "begin can only be called once");
-    TransactionContextFutureImpl begin =
-        new TransactionContextFutureImpl(this, internalBeginAsync(true));
-    return begin;
+    return new TransactionContextFutureImpl(this, internalBeginAsync(true));
   }
 
   private ApiFuture<TransactionContext> internalBeginAsync(boolean firstAttempt) {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/DatabaseAdminClientImpl.java

@@ -105,7 +105,7 @@ public OperationFuture<Database, RestoreDatabaseMetadata> restoreDatabase(Restor
     final OperationFuture<com.google.spanner.admin.database.v1.Database, RestoreDatabaseMetadata>
         rawOperationFuture = rpc.restoreDatabase(restore);
 
-    return new OperationFutureImpl<Database, RestoreDatabaseMetadata>(
+    return new OperationFutureImpl<>(
         rawOperationFuture.getPollingFuture(),
         rawOperationFuture.getInitialFuture(),
         new ApiFunction<OperationSnapshot, Database>() {
@@ -308,7 +308,7 @@ public OperationFuture<Database, CreateDatabaseMetadata> createDatabase(
         rawOperationFuture =
             rpc.createDatabase(
                 database.getId().getInstanceId().getName(), createStatement, statements, database);
-    return new OperationFutureImpl<Database, CreateDatabaseMetadata>(
+    return new OperationFutureImpl<>(
         rawOperationFuture.getPollingFuture(),
         rawOperationFuture.getInitialFuture(),
         new ApiFunction<OperationSnapshot, Database>() {
@@ -347,7 +347,7 @@ public OperationFuture<Void, UpdateDatabaseDdlMetadata> updateDatabaseDdl(
     final String opId = operationId != null ? operationId : randomOperationId();
     OperationFuture<Empty, UpdateDatabaseDdlMetadata> rawOperationFuture =
         rpc.updateDatabaseDdl(dbName, statements, opId);
-    return new OperationFutureImpl<Void, UpdateDatabaseDdlMetadata>(
+    return new OperationFutureImpl<>(
         rawOperationFuture.getPollingFuture(),
         rawOperationFuture.getInitialFuture(),
         new ApiFunction<OperationSnapshot, Void>() {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/InstanceAdminClientImpl.java

@@ -103,7 +103,7 @@ public OperationFuture<Instance, CreateInstanceMetadata> createInstance(Instance
         rawOperationFuture =
             rpc.createInstance(projectName, instance.getId().getInstance(), instance.toProto());
 
-    return new OperationFutureImpl<Instance, CreateInstanceMetadata>(
+    return new OperationFutureImpl<>(
         rawOperationFuture.getPollingFuture(),
         rawOperationFuture.getInitialFuture(),
         new ApiFunction<OperationSnapshot, Instance>() {
@@ -172,7 +172,7 @@ public OperationFuture<Instance, UpdateInstanceMetadata> updateInstance(
 
     OperationFuture<com.google.spanner.admin.instance.v1.Instance, UpdateInstanceMetadata>
         rawOperationFuture = rpc.updateInstance(instance.toProto(), fieldMask);
-    return new OperationFutureImpl<Instance, UpdateInstanceMetadata>(
+    return new OperationFutureImpl<>(
         rawOperationFuture.getPollingFuture(),
         rawOperationFuture.getInitialFuture(),
         new ApiFunction<OperationSnapshot, Instance>() {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/InstanceInfo.java

@@ -56,7 +56,7 @@ static FieldMask toFieldMask(InstanceField... fields) {
   }
 
   /** State of the Instance. */
-  public static enum State {
+  public enum State {
     UNSPECIFIED,
     CREATING,
     READY

google-cloud-spanner/src/main/java/com/google/cloud/spanner/Operation.java

@@ -45,7 +45,7 @@ public class Operation<R, M> {
           .setMaxRetryDelay(Duration.ofMinutes(500L))
           .build();
 
-  static interface Parser<R, M> {
+  interface Parser<R, M> {
     R parseResult(Any response);
 
     M parseMetadata(Any metadata);
@@ -85,7 +85,7 @@ private static <R, M> Operation<R, M> failed(
     SpannerException e =
         SpannerExceptionFactory.newSpannerException(
             ErrorCode.fromRpcStatus(status), status.getMessage(), null);
-    return new Operation<R, M>(rpc, name, metadata, null, e, true, parser, clock);
+    return new Operation<>(rpc, name, metadata, null, e, true, parser, clock);
   }
 
   private static <R, M> Operation<R, M> successful(