[java] UseEqualsToCompareStrings: Fix false positives

pmd-java/src/main/resources/category/java/errorprone.xml

@@ -3404,7 +3404,9 @@ public class Main {
           class="net.sourceforge.pmd.lang.rule.XPathRule"
           externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_errorprone.html#useequalstocomparestrings">
         <description>
-Using '==' or '!=' to compare strings only works if intern version is used on both sides.
+Using '==' or '!=' to compare strings only works if the internalized string (`String#intern()`)
+is used on both sides.
+
 Use the `equals()` method instead.
         </description>
         <priority>3</priority>
@@ -3412,7 +3414,8 @@ Use the `equals()` method instead.
             <property name="xpath">
                 <value>
 <![CDATA[
-//InfixExpression[count(*[pmd-java:typeIsExactly('java.lang.String')]) = 2]
+//InfixExpression[@Operator='==' or @Operator='!=']
+                 [count(*[pmd-java:typeIsExactly('java.lang.String')]) = 2]
 ]]>
                 </value>
             </property>

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/errorprone/xml/UseEqualsToCompareStrings.xml

@@ -184,4 +184,14 @@ public class O {
 }
         ]]></code>
     </test-code>
+
+    <test-code>
+        <description>False positive with string concatentation</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public class Foo {{
+    String a = "b" + "c";
+}}
+        ]]></code>
+    </test-code>
 </test-data>