diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPAddressWithMask.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPAddressWithMask.java
index aaaac3b..7cd8099 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPAddressWithMask.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPAddressWithMask.java
@@ -10,6 +10,8 @@
     }
 
     public abstract IPVersion getIpVersion();
+    
+    public abstract boolean contains(IPAddress<?> ip);
 
     public F getSubnetBroadcastAddress() {
         if (!mask.isCidrMask()) {
@@ -50,23 +52,4 @@
 
         return res.toString();
     }
-
-    public boolean contains(IPAddress<?> ip) {
-        Preconditions.checkNotNull(ip, "ip must not be null");
-
-        // Ensure mask and IP of the same version
-        if(getIpVersion() == ip.getIpVersion()) {
-            if(getIpVersion() == IPVersion.IPv4) {
-                IPv4AddressWithMask ipv4mask = (IPv4AddressWithMask) this;
-                IPv4Address ipv4 = (IPv4Address) ip;
-                return ipv4mask.matches(ipv4);
-            } else {
-                IPv6AddressWithMask ipv6mask = (IPv6AddressWithMask) this;
-                IPv6Address ipv6 = (IPv6Address) ip;
-                return ipv6mask.matches(ipv6);
-            }
-        }
-        return false;
-    }
-
 }
diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java
index 9b60c6a..3d14acf 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv4AddressWithMask.java
@@ -80,5 +80,14 @@
             return IPv4AddressWithMask.of(ipv4, IPv4Address.of(mask));
         }
     }
-
+    
+    @Override
+    public boolean contains(IPAddress<?> ip) {
+        if (ip == null) {
+            throw new NullPointerException("ip must not be null");
+        }
+        
+        IPv4Address ipv4 = (IPv4Address) ip;
+        return this.matches(ipv4);
+    }
 }
diff --git a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv6AddressWithMask.java b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv6AddressWithMask.java
index 7259c7f..2e7ff5e 100644
--- a/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv6AddressWithMask.java
+++ b/java_gen/pre-written/src/main/java/org/projectfloodlight/openflow/types/IPv6AddressWithMask.java
@@ -88,5 +88,14 @@
         }
     }
 
+    @Override
+    public boolean contains(IPAddress<?> ip) {
+        if (string == null) {
+            throw new NullPointerException("String must not be null");
+        }
+        
+        IPv6Address ipv6 = (IPv6Address) ip;
+        return this.matches(ipv6);
+    }
 
 }
diff --git a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java
index 2f59797..cbab734 100644
--- a/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java
+++ b/java_gen/pre-written/src/test/java/org/projectfloodlight/openflow/types/IPAddressTest.java
@@ -94,7 +94,8 @@
         assertFalse(mask.contains(invalidIpv4));
     }
 
-    @Test public void testContainsException() {
+    @Test 
+    public void testContainsException() {
         try {
             IPAddressWithMask<?> mask = IPAddressWithMask.of("1.2.3.4/24");
             mask.contains(null);