[#319] Checkstyle: enforce operators' placement in line wraps (#382)

Our coding standard for Java requires operators' placement in line
wraps to follow specific rules, such as having assignment operator (=)
stay attached to the token that precedes it and having the arithmetric
operator (+) in a new line. These rules are not enforced by
checkstyle.

Let's teach Checkstyle to be stricter about line wrapping around more
symbols by adding the relevant OperatorWrap rules.

build.gradle

@@ -42,7 +42,7 @@ allprojects {
         junitVersion = '4.12'
         testFxVersion = '4.0.5-alpha'
         monocleVersion = '1.8.0_20'
-        checkstyleVersion = '7.1.2'
+        checkstyleVersion = '7.2'
 
         libDir = 'lib'
     }

config/checkstyle/checkstyle.xml

@@ -322,6 +322,28 @@
       <property name="message" value="Trailing whitespace"/>
     </module>
 
+    <module name="OperatorWrap">
+      <!-- Checks that the non-assignment type operator is at the next line in a line wrap.
+           This includes "?", ":", "==", "!=", "/", "+", "-", "*", "%", ">>", ">>>",
+           ">=", ">", "<<", "<=", "<", "^", "|", "||", "&", "&&", "instanceof",
+           "&" when used in a generic upper or lower bounds constraints,
+             e.g. <T extends Foo & Bar>
+           "::" when used as a reference to a method or constructor without arguments.
+             e.g. String::compareToIgnoreCase
+      -->
+      <property name="tokens" value="QUESTION, COLON, EQUAL, NOT_EQUAL, DIV, PLUS, MINUS, STAR, MOD, SR, BSR,
+        GE, GT, SL, LE, LT, BXOR, BOR, LOR, BAND, LAND, LITERAL_INSTANCEOF, TYPE_EXTENSION_AND, METHOD_REF"/>
+      <property name="option" value="nl"/>
+    </module>
+    <module name="OperatorWrap">
+      <!-- Checks that the assignment type operator is at the previous end of line in a line wrap.
+           This includes "=", "/=", "+=", "-=", "*=", "%=", ">>=", ">>>=", "<<=", "^=", "&=".
+      -->
+      <property name="tokens" value="ASSIGN, DIV_ASSIGN, PLUS_ASSIGN, MINUS_ASSIGN, STAR_ASSIGN, MOD_ASSIGN,
+        SR_ASSIGN, BSR_ASSIGN, SL_ASSIGN, BXOR_ASSIGN, BOR_ASSIGN, BAND_ASSIGN"/>
+      <property name="option" value="eol"/>
+    </module>
+
     <module name="SeparatorWrap">
       <!-- Checks that the ".", "@" is at the next line in a line wrap. -->
       <property name="tokens" value="DOT, AT"/>

src/main/java/seedu/address/MainApp.java

@@ -121,8 +121,8 @@ protected Config initConfig(String configFilePath) {
             Optional<Config> configOptional = ConfigUtil.readConfig(configFilePathUsed);
             initializedConfig = configOptional.orElse(new Config());
         } catch (DataConversionException e) {
-            logger.warning("Config file at " + configFilePathUsed + " is not in the correct format. " +
-                    "Using default config properties");
+            logger.warning("Config file at " + configFilePathUsed + " is not in the correct format. "
+                    + "Using default config properties");
             initializedConfig = new Config();
         }
 
@@ -144,8 +144,8 @@ protected UserPrefs initPrefs(UserPrefsStorage storage) {
             Optional<UserPrefs> prefsOptional = storage.readUserPrefs();
             initializedPrefs = prefsOptional.orElse(new UserPrefs());
         } catch (DataConversionException e) {
-            logger.warning("UserPrefs file at " + prefsFilePath + " is not in the correct format. " +
-                    "Using default user prefs");
+            logger.warning("UserPrefs file at " + prefsFilePath + " is not in the correct format. "
+                    + "Using default user prefs");
             initializedPrefs = new UserPrefs();
         } catch (IOException e) {
             logger.warning("Problem while reading from the file. Will be starting with an empty AddressBook");

src/main/java/seedu/address/commons/core/Version.java

@@ -71,11 +71,22 @@ public String toString() {
 
     @Override
     public int compareTo(Version other) {
-        return this.major != other.major ? this.major - other.major :
-               this.minor != other.minor ? this.minor - other.minor :
-               this.patch != other.patch ? this.patch - other.patch :
-               this.isEarlyAccess == other.isEarlyAccess() ? 0 :
-               this.isEarlyAccess ? -1 : 1;
+        if (this.major != other.major) {
+            return this.major - other.major;
+        }
+        if (this.minor != other.minor) {
+            return this.minor - other.minor;
+        }
+        if (this.patch != other.patch) {
+            return this.patch - other.patch;
+        }
+        if (this.isEarlyAccess == other.isEarlyAccess()) {
+            return 0;
+        }
+        if (this.isEarlyAccess) {
+            return -1;
+        }
+        return 1;
     }
 
     @Override

src/test/java/guitests/guihandles/PersonListPanelHandle.java

@@ -55,8 +55,8 @@ public boolean isListMatching(ReadOnlyPerson... persons) {
      */
     public boolean isListMatching(int startPosition, ReadOnlyPerson... persons) throws IllegalArgumentException {
         if (persons.length + startPosition != getListView().getItems().size()) {
-            throw new IllegalArgumentException("List size mismatched\n" +
-                    "Expected " + (getListView().getItems().size() - 1) + " persons");
+            throw new IllegalArgumentException("List size mismatched\n"
+                    + "Expected " + (getListView().getItems().size() - 1) + " persons");
         }
         assertTrue(this.containsInOrder(startPosition, persons));
         for (int i = 0; i < persons.length; i++) {

src/test/java/seedu/address/commons/core/ConfigTest.java

@@ -14,9 +14,9 @@ public class ConfigTest {
 
     @Test
     public void toString_defaultObject_stringReturned() {
-        String defaultConfigAsString = "App title : Address App\n" +
-                "Current log level : INFO\n" +
-                "Preference file Location : preferences.json";
+        String defaultConfigAsString = "App title : Address App\n"
+                + "Current log level : INFO\n"
+                + "Preference file Location : preferences.json";
 
         assertEquals(defaultConfigAsString, new Config().toString());
     }