diff --git a/prism/include/JDDNode.h b/prism/include/JDDNode.h
index e2e7063f..28d6599d 100644
--- a/prism/include/JDDNode.h
+++ b/prism/include/JDDNode.h
@@ -13,7 +13,7 @@ extern "C" {
  * Signature: (J)Z
  */
 JNIEXPORT jboolean JNICALL Java_jdd_JDDNode_DDN_1IsConstant
-  (JNIEnv *, jobject, jlong);
+  (JNIEnv *, jclass, jlong);
 
 /*
  * Class:     jdd_JDDNode
@@ -21,7 +21,7 @@ JNIEXPORT jboolean JNICALL Java_jdd_JDDNode_DDN_1IsConstant
  * Signature: (J)I
  */
 JNIEXPORT jint JNICALL Java_jdd_JDDNode_DDN_1GetIndex
-  (JNIEnv *, jobject, jlong);
+  (JNIEnv *, jclass, jlong);
 
 /*
  * Class:     jdd_JDDNode
@@ -29,7 +29,7 @@ JNIEXPORT jint JNICALL Java_jdd_JDDNode_DDN_1GetIndex
  * Signature: (J)D
  */
 JNIEXPORT jdouble JNICALL Java_jdd_JDDNode_DDN_1GetValue
-  (JNIEnv *, jobject, jlong);
+  (JNIEnv *, jclass, jlong);
 
 /*
  * Class:     jdd_JDDNode
@@ -37,7 +37,7 @@ JNIEXPORT jdouble JNICALL Java_jdd_JDDNode_DDN_1GetValue
  * Signature: (J)J
  */
 JNIEXPORT jlong JNICALL Java_jdd_JDDNode_DDN_1GetThen
-  (JNIEnv *, jobject, jlong);
+  (JNIEnv *, jclass, jlong);
 
 /*
  * Class:     jdd_JDDNode
@@ -45,7 +45,7 @@ JNIEXPORT jlong JNICALL Java_jdd_JDDNode_DDN_1GetThen
  * Signature: (J)J
  */
 JNIEXPORT jlong JNICALL Java_jdd_JDDNode_DDN_1GetElse
-  (JNIEnv *, jobject, jlong);
+  (JNIEnv *, jclass, jlong);
 
 #ifdef __cplusplus
 }
diff --git a/prism/src/jdd/JDD.cc b/prism/src/jdd/JDD.cc
index 14c4e77a..6a906a2f 100644
--- a/prism/src/jdd/JDD.cc
+++ b/prism/src/jdd/JDD.cc
@@ -781,7 +781,7 @@ JNIEXPORT void JNICALL Java_jdd_JDD_DD_1ExportMatrixToSpyFile(JNIEnv *env, jclas
 //	
 //==============================================================================
 
-JNIEXPORT jboolean JNICALL Java_jdd_JDDNode_DDN_1IsConstant(JNIEnv *env, jobject obj, jlong __jlongpointer dd)
+JNIEXPORT jboolean JNICALL Java_jdd_JDDNode_DDN_1IsConstant(JNIEnv *env, jclass cls, jlong __jlongpointer dd)
 {
 	return Cudd_IsConstant(jlong_to_DdNode(dd));
 }
@@ -789,7 +789,7 @@ JNIEXPORT jboolean JNICALL Java_jdd_JDDNode_DDN_1IsConstant(JNIEnv *env, jobject
 //------------------------------------------------------------------------------
 
 
-JNIEXPORT jint JNICALL Java_jdd_JDDNode_DDN_1GetIndex(JNIEnv *env, jobject obj, jlong __jlongpointer dd)
+JNIEXPORT jint JNICALL Java_jdd_JDDNode_DDN_1GetIndex(JNIEnv *env, jclass cls, jlong __jlongpointer dd)
 {
 	return (jlong_to_DdNode(dd))->index;
 }
@@ -797,7 +797,7 @@ JNIEXPORT jint JNICALL Java_jdd_JDDNode_DDN_1GetIndex(JNIEnv *env, jobject obj,
 //------------------------------------------------------------------------------
 
 
-JNIEXPORT jdouble JNICALL Java_jdd_JDDNode_DDN_1GetValue(JNIEnv *env, jobject obj, jlong __jlongpointer dd)
+JNIEXPORT jdouble JNICALL Java_jdd_JDDNode_DDN_1GetValue(JNIEnv *env, jclass cls, jlong __jlongpointer dd)
 {
 	return Cudd_V(jlong_to_DdNode(dd));
 }
@@ -805,7 +805,7 @@ JNIEXPORT jdouble JNICALL Java_jdd_JDDNode_DDN_1GetValue(JNIEnv *env, jobject ob
 //------------------------------------------------------------------------------
 
 
-JNIEXPORT jlong __jlongpointer JNICALL Java_jdd_JDDNode_DDN_1GetThen(JNIEnv *env, jobject obj, jlong __jlongpointer dd)
+JNIEXPORT jlong __jlongpointer JNICALL Java_jdd_JDDNode_DDN_1GetThen(JNIEnv *env, jclass cls, jlong __jlongpointer dd)
 {
 	return ptr_to_jlong(Cudd_T(jlong_to_DdNode(dd)));
 }
@@ -813,7 +813,7 @@ JNIEXPORT jlong __jlongpointer JNICALL Java_jdd_JDDNode_DDN_1GetThen(JNIEnv *env
 //------------------------------------------------------------------------------
 
 
-JNIEXPORT jlong __jlongpointer JNICALL Java_jdd_JDDNode_DDN_1GetElse(JNIEnv *env, jobject obj, jlong __jlongpointer dd)
+JNIEXPORT jlong __jlongpointer JNICALL Java_jdd_JDDNode_DDN_1GetElse(JNIEnv *env, jclass cls, jlong __jlongpointer dd)
 {
 	return ptr_to_jlong(Cudd_E(jlong_to_DdNode(dd)));
 }
diff --git a/prism/src/jdd/JDDNode.java b/prism/src/jdd/JDDNode.java
index 790829b9..11395650 100644
--- a/prism/src/jdd/JDDNode.java
+++ b/prism/src/jdd/JDDNode.java
@@ -32,11 +32,11 @@ public class JDDNode
 	private long ptr;
 	
 	// native methods (jni)
-	private native boolean DDN_IsConstant(long dd);
-	private native int DDN_GetIndex(long dd);
-	private native double DDN_GetValue(long dd);
-	private native long DDN_GetThen(long dd);
-	private native long DDN_GetElse(long dd);
+	protected static native boolean DDN_IsConstant(long dd);
+	protected static native int DDN_GetIndex(long dd);
+	protected static native double DDN_GetValue(long dd);
+	protected static native long DDN_GetThen(long dd);
+	protected static native long DDN_GetElse(long dd);
 
 	static
 	{