[SPARK-13702][CORE][SQL][MLLIB] Use diamond operator for generic instance creation in Java code.

## What changes were proposed in this pull request?

In order to make `docs/examples` (and other related code) more simple/readable/user-friendly, this PR replaces existing codes like the followings by using `diamond` operator.

```
-    final ArrayList<Product2<Object, Object>> dataToWrite =
-      new ArrayList<Product2<Object, Object>>();
+    final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
```

Java 7 or higher supports **diamond** operator which replaces the type arguments required to invoke the constructor of a generic class with an empty set of type parameters (<>). Currently, Spark Java code use mixed usage of this.

## How was this patch tested?

Manual.
Pass the existing tests.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11541 from dongjoon-hyun/SPARK-13702.

8 files changed, 29 insertions, 29 deletions

diff --git a/launcher/src/main/java/org/apache/spark/launcher/AbstractCommandBuilder.java b/launcher/src/main/java/org/apache/spark/launcher/AbstractCommandBuilder.java
index c7ab51357c..46410327a5 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/AbstractCommandBuilder.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/AbstractCommandBuilder.java
@@ -58,12 +58,12 @@ abstract class AbstractCommandBuilder {
   private Map<String, String> effectiveConfig;
 
   public AbstractCommandBuilder() {
-    this.appArgs = new ArrayList<String>();
-    this.childEnv = new HashMap<String, String>();
-    this.conf = new HashMap<String, String>();
-    this.files = new ArrayList<String>();
-    this.jars = new ArrayList<String>();
-    this.pyFiles = new ArrayList<String>();
+    this.appArgs = new ArrayList<>();
+    this.childEnv = new HashMap<>();
+    this.conf = new HashMap<>();
+    this.files = new ArrayList<>();
+    this.jars = new ArrayList<>();
+    this.pyFiles = new ArrayList<>();
   }
 
   /**
@@ -87,7 +87,7 @@ abstract class AbstractCommandBuilder {
    * class.
    */
   List<String> buildJavaCommand(String extraClassPath) throws IOException {
-    List<String> cmd = new ArrayList<String>();
+    List<String> cmd = new ArrayList<>();
     String envJavaHome;
 
     if (javaHome != null) {
@@ -134,7 +134,7 @@ abstract class AbstractCommandBuilder {
   List<String> buildClassPath(String appClassPath) throws IOException {
     String sparkHome = getSparkHome();
 
-    List<String> cp = new ArrayList<String>();
+    List<String> cp = new ArrayList<>();
     addToClassPath(cp, getenv("SPARK_CLASSPATH"));
     addToClassPath(cp, appClassPath);
 
diff --git a/launcher/src/main/java/org/apache/spark/launcher/CommandBuilderUtils.java b/launcher/src/main/java/org/apache/spark/launcher/CommandBuilderUtils.java
index e328c8a341..7942d7372f 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/CommandBuilderUtils.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/CommandBuilderUtils.java
@@ -147,7 +147,7 @@ class CommandBuilderUtils {
    * Output: [ "ab cd", "efgh", "i \" j" ]
    */
   static List<String> parseOptionString(String s) {
-    List<String> opts = new ArrayList<String>();
+    List<String> opts = new ArrayList<>();
     StringBuilder opt = new StringBuilder();
     boolean inOpt = false;
     boolean inSingleQuote = false;
diff --git a/launcher/src/main/java/org/apache/spark/launcher/LauncherServer.java b/launcher/src/main/java/org/apache/spark/launcher/LauncherServer.java
index 414ffc2c84..69fbf4387b 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/LauncherServer.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/LauncherServer.java
@@ -129,7 +129,7 @@ class LauncherServer implements Closeable {
       server.setReuseAddress(true);
       server.bind(new InetSocketAddress(InetAddress.getLoopbackAddress(), 0));
 
-      this.clients = new ArrayList<ServerConnection>();
+      this.clients = new ArrayList<>();
       this.threadIds = new AtomicLong();
       this.factory = new NamedThreadFactory(THREAD_NAME_FMT);
       this.pending = new ConcurrentHashMap<>();
diff --git a/launcher/src/main/java/org/apache/spark/launcher/Main.java b/launcher/src/main/java/org/apache/spark/launcher/Main.java
index e751e948e3..1e34bb8c73 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/Main.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/Main.java
@@ -50,7 +50,7 @@ class Main {
   public static void main(String[] argsArray) throws Exception {
     checkArgument(argsArray.length > 0, "Not enough arguments: missing class name.");
 
-    List<String> args = new ArrayList<String>(Arrays.asList(argsArray));
+    List<String> args = new ArrayList<>(Arrays.asList(argsArray));
     String className = args.remove(0);
 
     boolean printLaunchCommand = !isEmpty(System.getenv("SPARK_PRINT_LAUNCH_COMMAND"));
@@ -70,7 +70,7 @@ class Main {
           // Ignore parsing exceptions.
         }
 
-        List<String> help = new ArrayList<String>();
+        List<String> help = new ArrayList<>();
         if (parser.className != null) {
           help.add(parser.CLASS);
           help.add(parser.className);
@@ -82,7 +82,7 @@ class Main {
       builder = new SparkClassCommandBuilder(className, args);
     }
 
-    Map<String, String> env = new HashMap<String, String>();
+    Map<String, String> env = new HashMap<>();
     List<String> cmd = builder.buildCommand(env);
     if (printLaunchCommand) {
       System.err.println("Spark Command: " + join(" ", cmd));
@@ -130,7 +130,7 @@ class Main {
       return cmd;
     }
 
-    List<String> newCmd = new ArrayList<String>();
+    List<String> newCmd = new ArrayList<>();
     newCmd.add("env");
 
     for (Map.Entry<String, String> e : childEnv.entrySet()) {
diff --git a/launcher/src/main/java/org/apache/spark/launcher/SparkClassCommandBuilder.java b/launcher/src/main/java/org/apache/spark/launcher/SparkClassCommandBuilder.java
index e575fd3308..40187236f2 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/SparkClassCommandBuilder.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/SparkClassCommandBuilder.java
@@ -44,7 +44,7 @@ class SparkClassCommandBuilder extends AbstractCommandBuilder {
 
   @Override
   public List<String> buildCommand(Map<String, String> env) throws IOException {
-    List<String> javaOptsKeys = new ArrayList<String>();
+    List<String> javaOptsKeys = new ArrayList<>();
     String memKey = null;
     String extraClassPath = null;
 
diff --git a/launcher/src/main/java/org/apache/spark/launcher/SparkLauncher.java b/launcher/src/main/java/org/apache/spark/launcher/SparkLauncher.java
index 20e6003a00..a542159901 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/SparkLauncher.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/SparkLauncher.java
@@ -75,7 +75,7 @@ public class SparkLauncher {
   /** Used internally to create unique logger names. */
   private static final AtomicInteger COUNTER = new AtomicInteger();
 
-  static final Map<String, String> launcherConfig = new HashMap<String, String>();
+  static final Map<String, String> launcherConfig = new HashMap<>();
 
   /**
    * Set a configuration value for the launcher library. These config values do not affect the
@@ -428,7 +428,7 @@ public class SparkLauncher {
   }
 
   private ProcessBuilder createBuilder() {
-    List<String> cmd = new ArrayList<String>();
+    List<String> cmd = new ArrayList<>();
     String script = isWindows() ? "spark-submit.cmd" : "spark-submit";
     cmd.add(join(File.separator, builder.getSparkHome(), "bin", script));
     cmd.addAll(builder.buildSparkSubmitArgs());
@@ -437,7 +437,7 @@ public class SparkLauncher {
     // preserved, otherwise the batch interpreter will mess up the arguments. Batch scripts are
     // weird.
     if (isWindows()) {
-      List<String> winCmd = new ArrayList<String>();
+      List<String> winCmd = new ArrayList<>();
       for (String arg : cmd) {
         winCmd.add(quoteForBatchScript(arg));
       }
diff --git a/launcher/src/main/java/org/apache/spark/launcher/SparkSubmitCommandBuilder.java b/launcher/src/main/java/org/apache/spark/launcher/SparkSubmitCommandBuilder.java
index 269c89c310..b2dd6ac4c3 100644
--- a/launcher/src/main/java/org/apache/spark/launcher/SparkSubmitCommandBuilder.java
+++ b/launcher/src/main/java/org/apache/spark/launcher/SparkSubmitCommandBuilder.java
@@ -67,7 +67,7 @@ class SparkSubmitCommandBuilder extends AbstractCommandBuilder {
    * command line parsing works. This maps the class name to the resource to use when calling
    * spark-submit.
    */
-  private static final Map<String, String> specialClasses = new HashMap<String, String>();
+  private static final Map<String, String> specialClasses = new HashMap<>();
   static {
     specialClasses.put("org.apache.spark.repl.Main", "spark-shell");
     specialClasses.put("org.apache.spark.sql.hive.thriftserver.SparkSQLCLIDriver",
@@ -87,12 +87,12 @@ class SparkSubmitCommandBuilder extends AbstractCommandBuilder {
   private boolean allowsMixedArguments;
 
   SparkSubmitCommandBuilder() {
-    this.sparkArgs = new ArrayList<String>();
+    this.sparkArgs = new ArrayList<>();
     this.printInfo = false;
   }
 
   SparkSubmitCommandBuilder(List<String> args) {
-    this.sparkArgs = new ArrayList<String>();
+    this.sparkArgs = new ArrayList<>();
     List<String> submitArgs = args;
     if (args.size() > 0 && args.get(0).equals(PYSPARK_SHELL)) {
       this.allowsMixedArguments = true;
@@ -123,7 +123,7 @@ class SparkSubmitCommandBuilder extends AbstractCommandBuilder {
   }
 
   List<String> buildSparkSubmitArgs() {
-    List<String> args = new ArrayList<String>();
+    List<String> args = new ArrayList<>();
     SparkSubmitOptionParser parser = new SparkSubmitOptionParser();
 
     if (verbose) {
@@ -244,7 +244,7 @@ class SparkSubmitCommandBuilder extends AbstractCommandBuilder {
 
     // The executable is the PYSPARK_DRIVER_PYTHON env variable set by the pyspark script,
     // followed by PYSPARK_DRIVER_PYTHON_OPTS.
-    List<String> pyargs = new ArrayList<String>();
+    List<String> pyargs = new ArrayList<>();
     pyargs.add(firstNonEmpty(System.getenv("PYSPARK_DRIVER_PYTHON"), "python"));
     String pyOpts = System.getenv("PYSPARK_DRIVER_PYTHON_OPTS");
     if (!isEmpty(pyOpts)) {
@@ -270,7 +270,7 @@ class SparkSubmitCommandBuilder extends AbstractCommandBuilder {
     env.put("R_PROFILE_USER",
             join(File.separator, sparkHome, "R", "lib", "SparkR", "profile", "shell.R"));
 
-    List<String> args = new ArrayList<String>();
+    List<String> args = new ArrayList<>();
     args.add(firstNonEmpty(System.getenv("SPARKR_DRIVER_R"), "R"));
     return args;
   }
diff --git a/launcher/src/test/java/org/apache/spark/launcher/SparkSubmitCommandBuilderSuite.java b/launcher/src/test/java/org/apache/spark/launcher/SparkSubmitCommandBuilderSuite.java
index 6aad47adbc..d36731840b 100644
--- a/launcher/src/test/java/org/apache/spark/launcher/SparkSubmitCommandBuilderSuite.java
+++ b/launcher/src/test/java/org/apache/spark/launcher/SparkSubmitCommandBuilderSuite.java
@@ -73,7 +73,7 @@ public class SparkSubmitCommandBuilderSuite extends BaseSuite {
       "spark.randomOption=foo",
       parser.CONF,
       SparkLauncher.DRIVER_EXTRA_LIBRARY_PATH + "=/driverLibPath");
-    Map<String, String> env = new HashMap<String, String>();
+    Map<String, String> env = new HashMap<>();
     List<String> cmd = buildCommand(sparkSubmitArgs, env);
 
     assertTrue(findInStringList(env.get(CommandBuilderUtils.getLibPathEnvName()),
@@ -125,7 +125,7 @@ public class SparkSubmitCommandBuilderSuite extends BaseSuite {
       "--master=foo",
       "--deploy-mode=bar");
 
-    Map<String, String> env = new HashMap<String, String>();
+    Map<String, String> env = new HashMap<>();
     List<String> cmd = buildCommand(sparkSubmitArgs, env);
     assertEquals("python", cmd.get(cmd.size() - 1));
     assertEquals(
@@ -142,7 +142,7 @@ public class SparkSubmitCommandBuilderSuite extends BaseSuite {
       "script.py",
       "arg1");
 
-    Map<String, String> env = new HashMap<String, String>();
+    Map<String, String> env = new HashMap<>();
     List<String> cmd = buildCommand(sparkSubmitArgs, env);
 
     assertEquals("foo", findArgValue(cmd, "--master"));
@@ -178,7 +178,7 @@ public class SparkSubmitCommandBuilderSuite extends BaseSuite {
           + "/launcher/src/test/resources");
     }
 
-    Map<String, String> env = new HashMap<String, String>();
+    Map<String, String> env = new HashMap<>();
     List<String> cmd = launcher.buildCommand(env);
 
     // Checks below are different for driver and non-driver mode.
@@ -258,7 +258,7 @@ public class SparkSubmitCommandBuilderSuite extends BaseSuite {
   }
 
   private Map<String, String> parseConf(List<String> cmd, SparkSubmitOptionParser parser) {
-    Map<String, String> conf = new HashMap<String, String>();
+    Map<String, String> conf = new HashMap<>();
     for (int i = 0; i < cmd.size(); i++) {
       if (cmd.get(i).equals(parser.CONF)) {
         String[] val = cmd.get(i + 1).split("=", 2);