diff --git a/gradlew b/gradlew
old mode 100644
new mode 100755
diff --git a/pom.xml b/pom.xml
index 927a989..d01283c 100644
--- a/pom.xml
+++ b/pom.xml
@@ -104,6 +104,9 @@
                 <configuration>
                     <source>1.8</source>
                     <target>1.8</target>
+                    <compilerArgs>
+                        <arg>-Xlint:unchecked</arg>
+                    </compilerArgs>
                 </configuration>
             </plugin>
             <plugin>
diff --git a/src/main/java/org/json/JSONArray.java b/src/main/java/org/json/JSONArray.java
index 50146a8..38b0b31 100644
--- a/src/main/java/org/json/JSONArray.java
+++ b/src/main/java/org/json/JSONArray.java
@@ -1359,7 +1359,8 @@ public class JSONArray implements Iterable<Object> {
      *            The subscript.
      * @param value
      *            The Map value.
-     * @return this.
+     * @return
+     *             reference to self
      * @throws JSONException
      *             If the index is negative or if the value is an invalid
      *             number.
@@ -1381,7 +1382,7 @@ public class JSONArray implements Iterable<Object> {
      *          The Map value.
      * @param jsonParserConfiguration
      *          Configuration object for the JSON parser
-     * @return
+     * @return reference to self
      * @throws JSONException
      *          If the index is negative or if the value is an invalid
      *          number.
diff --git a/src/main/java/org/json/JSONMLParserConfiguration.java b/src/main/java/org/json/JSONMLParserConfiguration.java
index b2514ab..43ba0db 100644
--- a/src/main/java/org/json/JSONMLParserConfiguration.java
+++ b/src/main/java/org/json/JSONMLParserConfiguration.java
@@ -55,11 +55,13 @@ public class JSONMLParserConfiguration extends ParserConfiguration {
         );
     }
 
+    @SuppressWarnings("unchecked")
     @Override
     public JSONMLParserConfiguration withKeepStrings(final boolean newVal) {
         return super.withKeepStrings(newVal);
     }
 
+    @SuppressWarnings("unchecked")
     @Override
     public JSONMLParserConfiguration withMaxNestingDepth(int maxNestingDepth) {
         return super.withMaxNestingDepth(maxNestingDepth);
diff --git a/src/main/java/org/json/JSONParserConfiguration.java b/src/main/java/org/json/JSONParserConfiguration.java
index 1ec1710..f95e244 100644
--- a/src/main/java/org/json/JSONParserConfiguration.java
+++ b/src/main/java/org/json/JSONParserConfiguration.java
@@ -17,6 +17,7 @@ public class JSONParserConfiguration extends ParserConfiguration {
     return new JSONParserConfiguration();
   }
 
+  @SuppressWarnings("unchecked")
   @Override
   public JSONParserConfiguration withMaxNestingDepth(final int maxNestingDepth) {
     return super.withMaxNestingDepth(maxNestingDepth);
diff --git a/src/main/java/org/json/ParserConfiguration.java b/src/main/java/org/json/ParserConfiguration.java
index 36fa508..ede2fc5 100644
--- a/src/main/java/org/json/ParserConfiguration.java
+++ b/src/main/java/org/json/ParserConfiguration.java
@@ -75,6 +75,7 @@ public class ParserConfiguration {
      * 
      * @return The existing configuration will not be modified. A new configuration is returned.
      */
+    @SuppressWarnings("unchecked")
     public <T extends ParserConfiguration> T withKeepStrings(final boolean newVal) {
         T newConfig = (T)this.clone();
         newConfig.keepStrings = newVal;
@@ -101,6 +102,7 @@ public class ParserConfiguration {
      * 
      * @return The existing configuration will not be modified. A new configuration is returned.
      */
+    @SuppressWarnings("unchecked")
     public <T extends ParserConfiguration> T withMaxNestingDepth(int maxNestingDepth) {
         T newConfig = (T)this.clone();
 
diff --git a/src/main/java/org/json/XMLParserConfiguration.java b/src/main/java/org/json/XMLParserConfiguration.java
index 2e4907f..0ac7834 100644
--- a/src/main/java/org/json/XMLParserConfiguration.java
+++ b/src/main/java/org/json/XMLParserConfiguration.java
@@ -192,6 +192,7 @@ public class XMLParserConfiguration extends ParserConfiguration {
      *
      * @return The existing configuration will not be modified. A new configuration is returned.
      */
+    @SuppressWarnings("unchecked")
     @Override
     public XMLParserConfiguration withKeepStrings(final boolean newVal) {
         return super.withKeepStrings(newVal);
@@ -309,6 +310,7 @@ public class XMLParserConfiguration extends ParserConfiguration {
      * @param maxNestingDepth the maximum nesting depth allowed to the XML parser
      * @return The existing configuration will not be modified. A new configuration is returned.
      */
+    @SuppressWarnings("unchecked")
     @Override
     public XMLParserConfiguration withMaxNestingDepth(int maxNestingDepth) {
         return super.withMaxNestingDepth(maxNestingDepth);
@@ -316,7 +318,7 @@ public class XMLParserConfiguration extends ParserConfiguration {
 
     /**
      * To enable explicit end tag with empty value.
-     * @param closeEmptyTag
+     * @param closeEmptyTag new value for the closeEmptyTag property
      * @return same instance of configuration with empty tag config updated
      */
     public XMLParserConfiguration withCloseEmptyTag(boolean closeEmptyTag){
diff --git a/src/test/java/org/json/junit/JSONObjectTest.java b/src/test/java/org/json/junit/JSONObjectTest.java
index 96f3673..053f17a 100644
--- a/src/test/java/org/json/junit/JSONObjectTest.java
+++ b/src/test/java/org/json/junit/JSONObjectTest.java
@@ -3760,6 +3760,48 @@ public class JSONObjectTest {
         String jsonString = object.toString();
     }
 
+    @Test(expected = JSONException.class)
+    public void testCircleReferenceFirstLevel() {
+        Map<Object, Object> jsonObject = new HashMap<>();
+
+        jsonObject.put("test", jsonObject);
+
+        new JSONObject(jsonObject, new JSONParserConfiguration());
+    }
+
+    @Test(expected = StackOverflowError.class)
+    public void testCircleReferenceMultiplyLevel_notConfigured_expectedStackOverflow() {
+        Map<Object, Object> inside = new HashMap<>();
+
+        Map<Object, Object> jsonObject = new HashMap<>();
+        inside.put("test", jsonObject);
+        jsonObject.put("test", inside);
+
+        new JSONObject(jsonObject, new JSONParserConfiguration().withMaxNestingDepth(99999));
+    }
+
+    @Test(expected = JSONException.class)
+    public void testCircleReferenceMultiplyLevel_configured_expectedJSONException() {
+        Map<Object, Object> inside = new HashMap<>();
+
+        Map<Object, Object> jsonObject = new HashMap<>();
+        inside.put("test", jsonObject);
+        jsonObject.put("test", inside);
+
+        new JSONObject(jsonObject, new JSONParserConfiguration());
+    }
+
+    @Test
+    public void testDifferentKeySameInstanceNotACircleReference() {
+        Map<Object, Object> map1 = new HashMap<>();
+        Map<Object, Object> map2 = new HashMap<>();
+
+        map1.put("test1", map2);
+        map1.put("test2", map2);
+
+        new JSONObject(map1);
+    }
+
     /**
      * Method to build nested map of max maxDepth
      *
diff --git a/src/test/java/org/json/junit/data/WeirdList.java b/src/test/java/org/json/junit/data/WeirdList.java
index 834b81e..3560586 100644
--- a/src/test/java/org/json/junit/data/WeirdList.java
+++ b/src/test/java/org/json/junit/data/WeirdList.java
@@ -12,7 +12,7 @@ import java.util.List;
  */
 public class WeirdList {
     /** */
-    private final List<Integer> list = new ArrayList();
+    private final List<Integer> list = new ArrayList<>();
 
     /**
      * @param vals
@@ -25,14 +25,14 @@ public class WeirdList {
      * @return a copy of the list
      */
     public List<Integer> get() {
-        return new ArrayList(this.list);
+        return new ArrayList<>(this.list);
     }
 
     /**
      * @return a copy of the list
      */
     public List<Integer> getALL() {
-        return new ArrayList(this.list);
+        return new ArrayList<>(this.list);
     }
 
     /**