[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.

1 files changed, 2 insertions, 2 deletions

diff --git a/common/network-common/src/main/java/org/apache/spark/network/client/TransportClientFactory.java b/common/network-common/src/main/java/org/apache/spark/network/client/TransportClientFactory.java
index 61bafc8380..1008c67de3 100644
--- a/common/network-common/src/main/java/org/apache/spark/network/client/TransportClientFactory.java
+++ b/common/network-common/src/main/java/org/apache/spark/network/client/TransportClientFactory.java
@@ -194,8 +194,8 @@ public class TransportClientFactory implements Closeable {
       .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, conf.connectionTimeoutMs())
       .option(ChannelOption.ALLOCATOR, pooledAllocator);
 
-    final AtomicReference<TransportClient> clientRef = new AtomicReference<TransportClient>();
-    final AtomicReference<Channel> channelRef = new AtomicReference<Channel>();
+    final AtomicReference<TransportClient> clientRef = new AtomicReference<>();
+    final AtomicReference<Channel> channelRef = new AtomicReference<>();
 
     bootstrap.handler(new ChannelInitializer<SocketChannel>() {
       @Override