diff --git a/server/sonar-server/src/main/java/org/sonar/server/issue/Result.java b/server/sonar-server/src/main/java/org/sonar/server/issue/Result.java
index 330f60e74ab7..49d56286d9a7 100644
--- a/server/sonar-server/src/main/java/org/sonar/server/issue/Result.java
+++ b/server/sonar-server/src/main/java/org/sonar/server/issue/Result.java
@@ -23,7 +23,6 @@
 
 import javax.annotation.CheckForNull;
 import javax.annotation.Nullable;
-
 import java.util.Arrays;
 import java.util.List;
 
@@ -124,7 +123,7 @@ public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
-      if (this.getClass() != o.getClass()) {
+      if (o == null || getClass() != o.getClass()) {
         return false;
       }
       Message message = (Message) o;
diff --git a/server/sonar-server/src/main/java/org/sonar/server/issue/RulesAggregation.java b/server/sonar-server/src/main/java/org/sonar/server/issue/RulesAggregation.java
index 8567a40d295c..920b84c60dc0 100644
--- a/server/sonar-server/src/main/java/org/sonar/server/issue/RulesAggregation.java
+++ b/server/sonar-server/src/main/java/org/sonar/server/issue/RulesAggregation.java
@@ -71,12 +71,17 @@ public boolean equals(Object o) {
       if (this == o) {
         return true;
       }
-      if (this.getClass() != o.getClass()) {
+      if (o == null || getClass() != o.getClass()) {
         return false;
       }
 
       Rule rule = (Rule) o;
-      return ruleKey.equals(rule.ruleKey);
+
+      if (!ruleKey.equals(rule.ruleKey)) {
+        return false;
+      }
+
+      return true;
     }
 
     @Override
diff --git a/sonar-duplications/src/main/java/org/sonar/duplications/detector/suffixtree/TextSet.java b/sonar-duplications/src/main/java/org/sonar/duplications/detector/suffixtree/TextSet.java
index 51ecbe542940..82ab1db55a66 100644
--- a/sonar-duplications/src/main/java/org/sonar/duplications/detector/suffixtree/TextSet.java
+++ b/sonar-duplications/src/main/java/org/sonar/duplications/detector/suffixtree/TextSet.java
@@ -19,10 +19,11 @@
  */
 package org.sonar.duplications.detector.suffixtree;
 
-import com.google.common.collect.Lists;
+import java.util.List;
+
 import org.sonar.duplications.block.Block;
 
-import java.util.List;
+import com.google.common.collect.Lists;
 
 /**
  * Simplifies construction of <a href="http://en.wikipedia.org/wiki/Generalised_suffix_tree">generalised suffix-tree</a>.
@@ -91,7 +92,7 @@ public Terminator(int i) {
 
     @Override
     public boolean equals(Object obj) {
-      return (this.getClass() == obj.getClass()) && (((Terminator) obj).stringNumber == stringNumber);
+      return (obj instanceof Terminator) && (((Terminator) obj).stringNumber == stringNumber);
     }
 
     @Override
diff --git a/sonar-duplications/src/main/java/org/sonar/duplications/index/CloneGroup.java b/sonar-duplications/src/main/java/org/sonar/duplications/index/CloneGroup.java
index b840c2f55f0c..01b7273da1cb 100644
--- a/sonar-duplications/src/main/java/org/sonar/duplications/index/CloneGroup.java
+++ b/sonar-duplications/src/main/java/org/sonar/duplications/index/CloneGroup.java
@@ -135,7 +135,7 @@ public String toString() {
    */
   @Override
   public boolean equals(Object object) {
-    if (this.getClass() != object.getClass()) {
+    if (!(object instanceof CloneGroup)) {
       return false;
     }
     CloneGroup another = (CloneGroup) object;
diff --git a/sonar-duplications/src/main/java/org/sonar/duplications/index/ClonePart.java b/sonar-duplications/src/main/java/org/sonar/duplications/index/ClonePart.java
index 630f52c1350f..6a569e27eae7 100644
--- a/sonar-duplications/src/main/java/org/sonar/duplications/index/ClonePart.java
+++ b/sonar-duplications/src/main/java/org/sonar/duplications/index/ClonePart.java
@@ -64,7 +64,7 @@ public int getLines() {
 
   @Override
   public boolean equals(Object obj) {
-    if (this.getClass() == obj.getClass()) {
+    if (obj instanceof ClonePart) {
       ClonePart another = (ClonePart) obj;
       return another.resourceId.equals(resourceId)
         && another.startLine == startLine
diff --git a/sonar-duplications/src/main/java/org/sonar/duplications/statement/Statement.java b/sonar-duplications/src/main/java/org/sonar/duplications/statement/Statement.java
index dc1c8ac402d1..49e9e90f743f 100644
--- a/sonar-duplications/src/main/java/org/sonar/duplications/statement/Statement.java
+++ b/sonar-duplications/src/main/java/org/sonar/duplications/statement/Statement.java
@@ -82,7 +82,7 @@ public int hashCode() {
 
   @Override
   public boolean equals(Object obj) {
-    if (this.getClass() != obj.getClass()) {
+    if (!(obj instanceof Statement)) {
       return false;
     }
     Statement other = (Statement) obj;
diff --git a/sonar-duplications/src/main/java/org/sonar/duplications/token/Token.java b/sonar-duplications/src/main/java/org/sonar/duplications/token/Token.java
index c1c374e7f52e..06525a4ccda9 100644
--- a/sonar-duplications/src/main/java/org/sonar/duplications/token/Token.java
+++ b/sonar-duplications/src/main/java/org/sonar/duplications/token/Token.java
@@ -50,7 +50,7 @@ public String getValue() {
 
   @Override
   public boolean equals(Object object) {
-    if (this.getClass() == object.getClass()) {
+    if (object instanceof Token) {
       Token anotherToken = (Token) object;
       return anotherToken.line == line && anotherToken.column == column && anotherToken.value.equals(value);
     }
diff --git a/sonar-plugin-api/src/main/java/org/sonar/api/notifications/Notification.java b/sonar-plugin-api/src/main/java/org/sonar/api/notifications/Notification.java
index 42eca231134e..0666e7260f12 100644
--- a/sonar-plugin-api/src/main/java/org/sonar/api/notifications/Notification.java
+++ b/sonar-plugin-api/src/main/java/org/sonar/api/notifications/Notification.java
@@ -121,8 +121,8 @@ public String getFieldValue(String field) {
   }
 
   @Override
-  public boolean equals(@Nullable Object obj) {
-    if (obj == null || this.getClass() != obj.getClass()) {
+  public boolean equals(Object obj) {
+    if (!(obj instanceof Notification)) {
       return false;
     }
     if (this == obj) {
diff --git a/sonar-plugin-api/src/main/java/org/sonar/api/rules/ActiveRuleParam.java b/sonar-plugin-api/src/main/java/org/sonar/api/rules/ActiveRuleParam.java
index 7f83179429f6..683f52cde435 100644
--- a/sonar-plugin-api/src/main/java/org/sonar/api/rules/ActiveRuleParam.java
+++ b/sonar-plugin-api/src/main/java/org/sonar/api/rules/ActiveRuleParam.java
@@ -104,12 +104,12 @@ public String getKey() {
 
   @Override
   public boolean equals(Object obj) {
+    if (!(obj instanceof ActiveRuleParam)) {
+      return false;
+    }
     if (this == obj) {
       return true;
     }
-    if (this.getClass() != obj.getClass()) {
-      return false;
-    }
     ActiveRuleParam other = (ActiveRuleParam) obj;
     return other.getKey().equals(getKey());
   }
diff --git a/sonar-plugin-api/src/main/java/org/sonar/api/server/debt/internal/DefaultDebtRemediationFunction.java b/sonar-plugin-api/src/main/java/org/sonar/api/server/debt/internal/DefaultDebtRemediationFunction.java
index 1445f50883d0..d9ac5cb78139 100644
--- a/sonar-plugin-api/src/main/java/org/sonar/api/server/debt/internal/DefaultDebtRemediationFunction.java
+++ b/sonar-plugin-api/src/main/java/org/sonar/api/server/debt/internal/DefaultDebtRemediationFunction.java
@@ -101,12 +101,12 @@ private void validate() {
 
   @Override
   public boolean equals(Object o) {
+    if (!(o instanceof DefaultDebtRemediationFunction)) {
+      return false;
+    }
     if (this == o) {
       return true;
     }
-    if (this.getClass() != o.getClass()) {
-      return false;
-    }
     DefaultDebtRemediationFunction other = (DefaultDebtRemediationFunction) o;
     return new EqualsBuilder()
       .append(coefficient, other.coefficient())