[SPARK-6990][BUILD] Add Java linting script; fix minor warnings

This replaces https://github.com/apache/spark/pull/9696

Invoke Checkstyle and print any errors to the console, failing the step.
Use Google's style rules modified according to
https://cwiki.apache.org/confluence/display/SPARK/Spark+Code+Style+Guide
Some important checks are disabled (see TODOs in `checkstyle.xml`) due to
multiple violations being present in the codebase.

Suggest fixing those TODOs in a separate PR(s).

More on Checkstyle can be found on the [official website](http://checkstyle.sourceforge.net/).

Sample output (from [build 46345](https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/46345/consoleFull)) (duplicated because I run the build twice with different profiles):

> Checkstyle checks failed at following occurrences:
[ERROR] src/main/java/org/apache/spark/sql/execution/datasources/parquet/UnsafeRowParquetRecordReader.java:[217,7] (coding) MissingSwitchDefault: switch without "default" clause.
> [ERROR] src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java:[198,10] (modifier) ModifierOrder: 'protected' modifier out of order with the JLS suggestions.
> [ERROR] src/main/java/org/apache/spark/sql/execution/datasources/parquet/UnsafeRowParquetRecordReader.java:[217,7] (coding) MissingSwitchDefault: switch without "default" clause.
> [ERROR] src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java:[198,10] (modifier) ModifierOrder: 'protected' modifier out of order with the JLS suggestions.
> [error] running /home/jenkins/workspace/SparkPullRequestBuilder2/dev/lint-java ; received return code 1

Also fix some of the minor violations that didn't require sweeping changes.

Apologies for the previous botched PRs - I finally figured out the issue.

cr: JoshRosen, pwendell

> I state that the contribution is my original work, and I license the work to the project under the project's open source license.

Author: Dmitry Erastov <derastov@gmail.com>

Closes #9867 from dskrvk/master.

4 files changed, 63 insertions, 29 deletions

diff --git a/sql/catalyst/src/main/java/org/apache/spark/sql/execution/UnsafeExternalRowSorter.java b/sql/catalyst/src/main/java/org/apache/spark/sql/execution/UnsafeExternalRowSorter.java
index 3986d6e18f..352002b349 100644
--- a/sql/catalyst/src/main/java/org/apache/spark/sql/execution/UnsafeExternalRowSorter.java
+++ b/sql/catalyst/src/main/java/org/apache/spark/sql/execution/UnsafeExternalRowSorter.java
@@ -51,7 +51,7 @@ final class UnsafeExternalRowSorter {
   private final PrefixComputer prefixComputer;
   private final UnsafeExternalSorter sorter;
 
-  public static abstract class PrefixComputer {
+  public abstract static class PrefixComputer {
     abstract long computePrefix(InternalRow row);
   }
 
diff --git a/sql/catalyst/src/main/java/org/apache/spark/sql/types/SQLUserDefinedType.java b/sql/catalyst/src/main/java/org/apache/spark/sql/types/SQLUserDefinedType.java
index df64a878b6..1e4e5ede8c 100644
--- a/sql/catalyst/src/main/java/org/apache/spark/sql/types/SQLUserDefinedType.java
+++ b/sql/catalyst/src/main/java/org/apache/spark/sql/types/SQLUserDefinedType.java
@@ -41,5 +41,5 @@ public @interface SQLUserDefinedType {
    * Returns an instance of the UserDefinedType which can serialize and deserialize the user
    * class to and from Catalyst built-in types.
    */
-  Class<? extends UserDefinedType<?> > udt();
+  Class<? extends UserDefinedType<?>> udt();
 }
diff --git a/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java b/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java
index 2ed30c1f5a..842dcb8c93 100644
--- a/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java
+++ b/sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/SpecificParquetRecordReaderBase.java
@@ -195,7 +195,7 @@ public abstract class SpecificParquetRecordReaderBase<T> extends RecordReader<Vo
    * Creates a reader for definition and repetition levels, returning an optimized one if
    * the levels are not needed.
    */
-  static protected IntIterator createRLEIterator(int maxLevel, BytesInput bytes,
+  protected static IntIterator createRLEIterator(int maxLevel, BytesInput bytes,
                                               ColumnDescriptor descriptor) throws IOException {
     try {
       if (maxLevel == 0) return new NullIntIterator();
diff --git a/sql/hive/src/test/java/org/apache/spark/sql/hive/test/Complex.java b/sql/hive/src/test/java/org/apache/spark/sql/hive/test/Complex.java
index e010112bb9..4ef1f276d1 100644
--- a/sql/hive/src/test/java/org/apache/spark/sql/hive/test/Complex.java
+++ b/sql/hive/src/test/java/org/apache/spark/sql/hive/test/Complex.java
@@ -489,6 +489,7 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
       }
       break;
 
+    default:
     }
   }
 
@@ -512,6 +513,7 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
     case M_STRING_STRING:
       return getMStringString();
 
+    default:
     }
     throw new IllegalStateException();
   }
@@ -535,75 +537,91 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
       return isSetLintString();
     case M_STRING_STRING:
       return isSetMStringString();
+    default:
     }
     throw new IllegalStateException();
   }
 
   @Override
   public boolean equals(Object that) {
-    if (that == null)
+    if (that == null) {
       return false;
-    if (that instanceof Complex)
+    }
+    if (that instanceof Complex) {
       return this.equals((Complex)that);
+    }
     return false;
   }
 
   public boolean equals(Complex that) {
-    if (that == null)
+    if (that == null) {
       return false;
+    }
 
     boolean this_present_aint = true;
     boolean that_present_aint = true;
     if (this_present_aint || that_present_aint) {
-      if (!(this_present_aint && that_present_aint))
+      if (!(this_present_aint && that_present_aint)) {
         return false;
-      if (this.aint != that.aint)
+      }
+      if (this.aint != that.aint) {
         return false;
+      }
     }
 
     boolean this_present_aString = true && this.isSetAString();
     boolean that_present_aString = true && that.isSetAString();
     if (this_present_aString || that_present_aString) {
-      if (!(this_present_aString && that_present_aString))
+      if (!(this_present_aString && that_present_aString)) {
         return false;
-      if (!this.aString.equals(that.aString))
+      }
+      if (!this.aString.equals(that.aString)) {
         return false;
+      }
     }
 
     boolean this_present_lint = true && this.isSetLint();
     boolean that_present_lint = true && that.isSetLint();
     if (this_present_lint || that_present_lint) {
-      if (!(this_present_lint && that_present_lint))
+      if (!(this_present_lint && that_present_lint)) {
         return false;
-      if (!this.lint.equals(that.lint))
+      }
+      if (!this.lint.equals(that.lint)) {
         return false;
+      }
     }
 
     boolean this_present_lString = true && this.isSetLString();
     boolean that_present_lString = true && that.isSetLString();
     if (this_present_lString || that_present_lString) {
-      if (!(this_present_lString && that_present_lString))
+      if (!(this_present_lString && that_present_lString)) {
         return false;
-      if (!this.lString.equals(that.lString))
+      }
+      if (!this.lString.equals(that.lString)) {
         return false;
+      }
     }
 
     boolean this_present_lintString = true && this.isSetLintString();
     boolean that_present_lintString = true && that.isSetLintString();
     if (this_present_lintString || that_present_lintString) {
-      if (!(this_present_lintString && that_present_lintString))
+      if (!(this_present_lintString && that_present_lintString)) {
         return false;
-      if (!this.lintString.equals(that.lintString))
+      }
+      if (!this.lintString.equals(that.lintString)) {
         return false;
+      }
     }
 
     boolean this_present_mStringString = true && this.isSetMStringString();
     boolean that_present_mStringString = true && that.isSetMStringString();
     if (this_present_mStringString || that_present_mStringString) {
-      if (!(this_present_mStringString && that_present_mStringString))
+      if (!(this_present_mStringString && that_present_mStringString)) {
         return false;
-      if (!this.mStringString.equals(that.mStringString))
+      }
+      if (!this.mStringString.equals(that.mStringString)) {
         return false;
+      }
     }
 
     return true;
@@ -615,33 +633,39 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
 
     boolean present_aint = true;
     builder.append(present_aint);
-    if (present_aint)
+    if (present_aint) {
       builder.append(aint);
+    }
 
     boolean present_aString = true && (isSetAString());
     builder.append(present_aString);
-    if (present_aString)
+    if (present_aString) {
       builder.append(aString);
+    }
 
     boolean present_lint = true && (isSetLint());
     builder.append(present_lint);
-    if (present_lint)
+    if (present_lint) {
       builder.append(lint);
+    }
 
     boolean present_lString = true && (isSetLString());
     builder.append(present_lString);
-    if (present_lString)
+    if (present_lString) {
       builder.append(lString);
+    }
 
     boolean present_lintString = true && (isSetLintString());
     builder.append(present_lintString);
-    if (present_lintString)
+    if (present_lintString) {
       builder.append(lintString);
+    }
 
     boolean present_mStringString = true && (isSetMStringString());
     builder.append(present_mStringString);
-    if (present_mStringString)
+    if (present_mStringString) {
       builder.append(mStringString);
+    }
 
     return builder.toHashCode();
   }
@@ -737,7 +761,9 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
     sb.append("aint:");
     sb.append(this.aint);
     first = false;
-    if (!first) sb.append(", ");
+    if (!first) {
+      sb.append(", ");
+    }
     sb.append("aString:");
     if (this.aString == null) {
       sb.append("null");
@@ -745,7 +771,9 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
       sb.append(this.aString);
     }
     first = false;
-    if (!first) sb.append(", ");
+    if (!first) {
+      sb.append(", ");
+    }
     sb.append("lint:");
     if (this.lint == null) {
       sb.append("null");
@@ -753,7 +781,9 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
       sb.append(this.lint);
     }
     first = false;
-    if (!first) sb.append(", ");
+    if (!first) {
+      sb.append(", ");
+    }
     sb.append("lString:");
     if (this.lString == null) {
       sb.append("null");
@@ -761,7 +791,9 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
       sb.append(this.lString);
     }
     first = false;
-    if (!first) sb.append(", ");
+    if (!first) {
+      sb.append(", ");
+    }
     sb.append("lintString:");
     if (this.lintString == null) {
       sb.append("null");
@@ -769,7 +801,9 @@ public class Complex implements org.apache.thrift.TBase<Complex, Complex._Fields
       sb.append(this.lintString);
     }
     first = false;
-    if (!first) sb.append(", ");
+    if (!first) {
+      sb.append(", ");
+    }
     sb.append("mStringString:");
     if (this.mStringString == null) {
       sb.append("null");