diff --git a/c/class_resolver.c b/c/class_resolver.c
index 0c96f5c..1cebaa8 100644
--- a/c/class_resolver.c
+++ b/c/class_resolver.c
@@ -73,7 +73,7 @@ struct hash_table_entry * class_resolver_load_from_filenames(const char * filena
         printf("\n");
 
         field_entry[i].field_info = &class_file->fields[i];
-        field_entry[i].value = 0;
+        field_entry[i].value64 = 0;
 
         hash_table_add(fields_hash_table_length,
                        fields_hash_table,
diff --git a/c/execute.c b/c/execute.c
index e73d8d8..9f90326 100644
--- a/c/execute.c
+++ b/c/execute.c
@@ -8,17 +8,27 @@
 
 void op_aaload(struct vm * vm)
 {
-  assert(!"op_aaload");
+  int32_t index = operand_stack_pop_u32(vm->current_frame);
+  int32_t * arrayref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  assert(arrayref[0] > 0 && index < arrayref[0]);
+  uint32_t * referencearray = (uint32_t *)&arrayref[1];
+  uint32_t value = referencearray[index];
+  operand_stack_push_u32(vm->current_frame, value);
 }
 
 void op_aastore(struct vm * vm)
 {
-  assert(!"op_aastore");
+  uint32_t value = operand_stack_pop_u32(vm->current_frame);
+  int32_t index = operand_stack_pop_u32(vm->current_frame);
+  int32_t * arrayref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  assert(arrayref[0] > 0 && index < arrayref[0]);
+  int32_t * referencearray = (int32_t *)&arrayref[1];
+  referencearray[index] = value;
 }
 
 void op_aconst_null(struct vm * vm)
 {
-  assert(!"op_aconst_null");
+  operand_stack_push_u32(vm->current_frame, 0);
 }
 
 void op_aload(struct vm * vm, uint32_t index)
@@ -53,12 +63,25 @@ void op_aload_3(struct vm * vm)
 
 void op_anewarray(struct vm * vm, uint32_t index)
 {
-  assert(!"op_anewarray");
+  int32_t count = operand_stack_pop_u32(vm->current_frame);
+  int32_t size = 4 * count + 4;
+  int32_t * arrayref = memory_allocate(size);
+  assert(arrayref != 0);
+  arrayref[0] = count;
+
+  /* All components of the new array are initialized to null, the default value
+     for reference types */
+  for (int i = 0; i < count; i++) {
+    arrayref[i + 1] = 0;
+  }
+
+  operand_stack_push_u32(vm->current_frame, (uint32_t)arrayref);
 }
 
 void op_areturn(struct vm * vm)
 {
-  assert(!"op_areturn");
+  assert(vm->current_frame->return_type == 'L');
+  vm_method_return(vm);
 }
 
 void op_arraylength(struct vm * vm)
@@ -105,12 +128,22 @@ void op_athrow(struct vm * vm)
 
 void op_baload(struct vm * vm)
 {
-  assert(!"op_baload");
+  int32_t index = operand_stack_pop_u32(vm->current_frame);
+  int32_t * arrayref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  assert(arrayref[0] > 0 && index < arrayref[0]);
+  int8_t * chararray = (int8_t *)&arrayref[1];
+  int8_t value = chararray[index];
+  operand_stack_push_u32(vm->current_frame, value);
 }
 
 void op_bastore(struct vm * vm)
 {
-  assert(!"op_bastore");
+  int8_t value = operand_stack_pop_u32(vm->current_frame);
+  int32_t index = operand_stack_pop_u32(vm->current_frame);
+  int32_t * arrayref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  assert(arrayref[0] > 0 && index < arrayref[0]);
+  int8_t * chararray = (int8_t *)&arrayref[1];
+  chararray[index] = value;
 }
 
 void op_bipush(struct vm * vm, int32_t byte)
@@ -707,7 +740,7 @@ void op_goto_w(struct vm * vm, int32_t branch)
 void op_i2b(struct vm * vm)
 {
   uint32_t value = operand_stack_pop_u32(vm->current_frame);
-  uint8_t result = value;
+  int8_t result = value;
   operand_stack_push_u32(vm->current_frame, result);
 }
 
@@ -827,12 +860,20 @@ void op_idiv(struct vm * vm)
 
 void op_if_acmpeq(struct vm * vm, int32_t branch)
 {
-  assert(!"op_if_acmpeq");
+  int32_t value2 = operand_stack_pop_u32(vm->current_frame);
+  int32_t value1 = operand_stack_pop_u32(vm->current_frame);
+  if (value1 == value2) {
+    vm->current_frame->pc = vm->current_frame->pc + branch;
+  }
 }
 
 void op_if_acmpne(struct vm * vm, int32_t branch)
 {
-  assert(!"op_if_acmpne");
+  int32_t value2 = operand_stack_pop_u32(vm->current_frame);
+  int32_t value1 = operand_stack_pop_u32(vm->current_frame);
+  if (value1 != value2) {
+    vm->current_frame->pc = vm->current_frame->pc + branch;
+  }
 }
 
 void op_if_icmpeq(struct vm * vm, int32_t branch)
@@ -1532,11 +1573,13 @@ void op_new(struct vm * vm, uint32_t index)
      reference to the instance, is pushed onto the operand stack. */
 
   int fields_count = class_entry->class_file->fields_count;
-  (void)fields_count;
-  int32_t * objectref = memory_allocate(fields_count * 2 * 4);
-  for (int i = 0; i < fields_count; i++) {
-    objectref[i * 2] = 0;
-    objectref[i * 2 + 1] = 0;
+  int32_t * objectref = (int32_t *)-1;
+  if (fields_count > 0) {
+    objectref = memory_allocate(fields_count * 2 * 4);
+    for (int i = 0; i < fields_count; i++) {
+      objectref[i * 2] = 0;
+      objectref[i * 2 + 1] = 0;
+    }
   }
 
   operand_stack_push_u32(vm->current_frame, (uint32_t)objectref);
@@ -1726,12 +1769,22 @@ void op_return(struct vm * vm)
 
 void op_saload(struct vm * vm)
 {
-  assert(!"op_saload");
+  int32_t index = operand_stack_pop_u32(vm->current_frame);
+  int32_t * arrayref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  assert(arrayref[0] > 0 && index < arrayref[0]);
+  int16_t * shortarray = (int16_t *)&arrayref[1];
+  int16_t value = shortarray[index];
+  operand_stack_push_u32(vm->current_frame, value);
 }
 
 void op_sastore(struct vm * vm)
 {
-  assert(!"op_sastore");
+  uint16_t value = operand_stack_pop_u32(vm->current_frame);
+  int32_t index = operand_stack_pop_u32(vm->current_frame);
+  int32_t * arrayref = (int32_t *)operand_stack_pop_u32(vm->current_frame);
+  assert(arrayref[0] > 0 && index < arrayref[0]);
+  int16_t * shortarray = (int16_t *)&arrayref[1];
+  shortarray[index] = value;
 }
 
 void op_sipush(struct vm * vm, int32_t byte)
diff --git a/c/frame.c b/c/frame.c
index a555ec0..5b4fc2e 100644
--- a/c/frame.c
+++ b/c/frame.c
@@ -47,7 +47,7 @@ int find_constantvalue_name_index(struct class_file * class_file)
   return 0;
 }
 
-static int descriptor_nargs(struct constant * descriptor_constant)
+static int descriptor_nargs(struct constant * descriptor_constant, uint8_t * return_type)
 {
   assert(descriptor_constant->tag == CONSTANT_Utf8);
   assert(descriptor_constant->utf8.length >= 2);
@@ -56,6 +56,7 @@ static int descriptor_nargs(struct constant * descriptor_constant)
   printf("method descriptor: ");
   print_utf8_string(descriptor_constant);
   printf("\n");
+  printf("args: `");
 
   int i = 1;
   int nargs = 0;
@@ -70,19 +71,37 @@ static int descriptor_nargs(struct constant * descriptor_constant)
     case 'J':
       nargs += 2;
       break;
+    case 'L':
+      nargs += 1;
+      while (descriptor_constant->utf8.bytes[i] != ';') i += 1;
+      break;
     default:
       nargs += 1;
       break;
     }
     i += 1;
   }
-  assert(i + 2 == descriptor_constant->utf8.length);
+  printf("\n");
+
+  *return_type = descriptor_constant->utf8.bytes[i + 1];
 
   return nargs;
 }
 
 bool vm_initialize_class(struct vm * vm, struct class_entry * class_entry)
 {
+  printf("vm_initialize_class: ");
+  struct constant * class_constant = &class_entry->class_file->constant_pool[class_entry->class_file->this_class - 1];
+  #ifdef DEBUG
+  assert(class_constant->tag == CONSTANT_Class);
+  #endif
+  struct constant * class_name_constant = &class_entry->class_file->constant_pool[class_constant->class.name_index - 1];
+  #ifdef DEBUG
+  assert(class_name_constant->tag == CONSTANT_Utf8);
+  #endif
+  print_constant(class_name_constant);
+  printf("\n");
+
   if (class_entry->initialization_state == CLASS_INITIALIZED)
     return true;
 
@@ -120,8 +139,8 @@ bool vm_initialize_class(struct vm * vm, struct class_entry * class_entry)
                                                                          name_constant->utf8.bytes,
                                                                          name_constant->utf8.length);
           assert(field_entry != nullptr);
-          field_entry->value = constantvalue->integer.bytes;
-          printf("  constantvalue: %d\n", field_entry->value);
+          field_entry->value32 = constantvalue->integer.bytes;
+          printf("  constantvalue: %d\n", field_entry->value32);
           break;
         }
       }
@@ -148,7 +167,13 @@ bool vm_initialize_class(struct vm * vm, struct class_entry * class_entry)
     vm->current_frame->next_pc = vm->current_frame->pc;
 
     vm_static_method_call(vm, class_file, method_info);
+
+    // tamper with initialization_frame
+    vm->current_frame->initialization_frame = class_entry;
     return false;
+  } else {
+    class_entry->initialization_state = CLASS_INITIALIZED;
+    printf("<clinit> does not exist for this class\n");
   }
 
   return true;
@@ -181,9 +206,10 @@ void vm_special_method_call(struct vm * vm, struct class_file * class_file, stru
   vm->current_frame->local_variable = stack_push_data(&vm->data_stack, code->max_locals);
   vm->current_frame->operand_stack = stack_push_data(&vm->data_stack, code->max_stack);
   vm->current_frame->operand_stack_ix = 0;
+  vm->current_frame->initialization_frame = nullptr;
 
   struct constant * descriptor_constant = &class_file->constant_pool[method_info->descriptor_index - 1];
-  int nargs = descriptor_nargs(descriptor_constant);
+  int nargs = descriptor_nargs(descriptor_constant, &vm->current_frame->return_type);
   nargs += 1;
   printf("nargs+1: %d\n", nargs);
   for (int i = 0; i < nargs; i++) {
@@ -191,7 +217,6 @@ void vm_special_method_call(struct vm * vm, struct class_file * class_file, stru
     printf("local[%d] = %x\n", nargs - i - 1, value);
     vm->current_frame->local_variable[nargs - i - 1] = value;
   }
-  vm->current_frame->return_type = descriptor_constant->utf8.bytes[descriptor_constant->utf8.length - 1];
 
   vm->current_frame->pc = 0;
   vm->current_frame->class = class_file;
@@ -227,16 +252,17 @@ void vm_static_method_call(struct vm * vm, struct class_file * class_file, struc
   vm->current_frame->local_variable = stack_push_data(&vm->data_stack, code->max_locals);
   vm->current_frame->operand_stack = stack_push_data(&vm->data_stack, code->max_stack);
   vm->current_frame->operand_stack_ix = 0;
+  vm->current_frame->initialization_frame = nullptr;
 
   struct constant * descriptor_constant = &class_file->constant_pool[method_info->descriptor_index - 1];
-  int nargs = descriptor_nargs(descriptor_constant);
+  int nargs = descriptor_nargs(descriptor_constant, &vm->current_frame->return_type);
   printf("nargs %d\n", nargs);
   for (int i = 0; i < nargs; i++) {
     uint32_t value = operand_stack_pop_u32(old_frame);
     printf("local[%d] = %x\n", nargs - i - 1, value);
     vm->current_frame->local_variable[nargs - i - 1] = value;
   }
-  vm->current_frame->return_type = descriptor_constant->utf8.bytes[descriptor_constant->utf8.length - 1];
+  ;
 
   vm->current_frame->pc = 0;
   vm->current_frame->class = class_file;
@@ -247,6 +273,13 @@ void vm_static_method_call(struct vm * vm, struct class_file * class_file, struc
 
 void vm_method_return(struct vm * vm)
 {
+  if (vm->current_frame->initialization_frame != nullptr) {
+    printf("vm_method_return: initialization_frame!=nullptr\n");
+    struct class_entry * class_entry = vm->current_frame->initialization_frame;
+    class_entry->initialization_state = CLASS_INITIALIZED;
+    vm->current_frame->initialization_frame = 0;
+  }
+
   struct frame * old_frame = vm->current_frame;
 
   stack_pop_data(&vm->data_stack, old_frame->code->max_locals);
@@ -282,12 +315,13 @@ void vm_method_return(struct vm * vm)
   */
 
   switch (old_frame->return_type) {
-  case 'Z': [[fallthrough]];
   case 'B': [[fallthrough]];
   case 'C': [[fallthrough]];
-  case 'S': [[fallthrough]];
+  case 'F': [[fallthrough]];
   case 'I': [[fallthrough]];
-  case 'F':
+  case 'L': [[fallthrough]];
+  case 'S': [[fallthrough]];
+  case 'Z':
     {
       uint32_t value = operand_stack_pop_u32(old_frame);
       operand_stack_push_u32(vm->current_frame, value);
@@ -304,6 +338,7 @@ void vm_method_return(struct vm * vm)
     break;
   default:
     fprintf(stderr, "return type not implemented: %c\n", old_frame->return_type);
+    assert(false);
     break;
   }
   assert(old_frame->operand_stack_ix == 0);
diff --git a/c/frame.h b/c/frame.h
index b9788d5..984911e 100644
--- a/c/frame.h
+++ b/c/frame.h
@@ -13,7 +13,8 @@ struct frame {
   uint32_t * operand_stack;
   uint32_t pc;
   uint32_t next_pc;
-  uint16_t operand_stack_ix;
+  int32_t operand_stack_ix;
+  struct class_entry * initialization_frame;
   uint8_t return_type;
 };
 
@@ -22,8 +23,8 @@ struct stack {
     struct frame * frame;
     uint32_t * data;
   };
-  uint32_t ix;
-  uint32_t capacity;
+  int32_t ix;
+  int32_t capacity;
 };
 
 struct vm {
@@ -35,7 +36,6 @@ struct vm {
     struct hash_table_entry * entry;
   } class_hash_table;
 };
-
 static inline struct frame * stack_push_frame(struct stack * stack, int num_frames)
 {
   struct frame * frame = &stack->frame[stack->ix];
@@ -77,6 +77,7 @@ static inline void operand_stack_push_u32(struct frame * frame, uint32_t value)
 static inline uint32_t operand_stack_pop_u32(struct frame * frame)
 {
   frame->operand_stack_ix--;
+  assert(frame->operand_stack_ix >= 0);
   uint32_t value = frame->operand_stack[frame->operand_stack_ix];
   frame->operand_stack[frame->operand_stack_ix] = -1;
   return value;
@@ -99,6 +100,7 @@ static inline void operand_stack_push_f32(struct frame * frame, float f)
 static inline float operand_stack_pop_f32(struct frame * frame)
 {
   frame->operand_stack_ix--;
+  assert(frame->operand_stack_ix >= 0);
   uint32_t value = frame->operand_stack[frame->operand_stack_ix];
   frame->operand_stack[frame->operand_stack_ix] = -1;
   float f = *((float *)&value);
@@ -116,8 +118,10 @@ static inline void operand_stack_push_u64(struct frame * frame, uint64_t value)
 static inline uint64_t operand_stack_pop_u64(struct frame * frame)
 {
   frame->operand_stack_ix--;
+  assert(frame->operand_stack_ix >= 0);
   uint64_t high = frame->operand_stack[frame->operand_stack_ix];
   frame->operand_stack_ix--;
+  assert(frame->operand_stack_ix >= 0);
   uint64_t low = frame->operand_stack[frame->operand_stack_ix];
   uint64_t value = (high << 32) | (low << 0);
   return value;
@@ -135,8 +139,10 @@ static inline void operand_stack_push_f64(struct frame * frame, double f)
 static inline double operand_stack_pop_f64(struct frame * frame)
 {
   frame->operand_stack_ix--;
+  assert(frame->operand_stack_ix >= 0);
   uint64_t high = frame->operand_stack[frame->operand_stack_ix];
   frame->operand_stack_ix--;
+  assert(frame->operand_stack_ix >= 0);
   uint64_t low = frame->operand_stack[frame->operand_stack_ix];
   uint64_t value = (high << 32) | (low << 0);
   double f = *((double *)&value);
diff --git a/p/ByteArray.java b/p/ByteArray.java
new file mode 100644
index 0000000..6ff21c4
--- /dev/null
+++ b/p/ByteArray.java
@@ -0,0 +1,17 @@
+package p;
+
+class ByteArray {
+    static byte test() {
+        byte[] l = new byte[10];
+        for (int i = 0; i < l.length; i++)
+            l[i] = (byte)(i * 3);
+        byte sum = 0;
+        for (int i = 0; i < l.length; i++)
+            sum += l[i];
+        return sum;
+    }
+
+    public static void main() {
+        System.out.println(test());
+    }
+}
diff --git a/p/NullReference.java b/p/NullReference.java
new file mode 100644
index 0000000..34b676e
--- /dev/null
+++ b/p/NullReference.java
@@ -0,0 +1,51 @@
+package p;
+
+class NullReference {
+    int field;
+
+    static int test() {
+        Object o = null;
+        if (o == null)
+            return 1;
+        else
+            return 0;
+    }
+
+    static NullReference test2(NullReference r) {
+        NullReference b = new NullReference();
+        b.field = 39;
+        return b;
+    }
+
+    static int test3() {
+        NullReference a = new NullReference();
+        a.field = 12;
+        NullReference c = test2(a);
+
+        if (a != c)
+            c.field += 1000;
+
+        return c.field;
+    }
+
+    static int test4() {
+        Object[] oa = new Object[10];
+        for (int i = 0; i < oa.length; i++) {
+            if (i % 2 == 0)
+                oa[i] = null;
+            else
+                oa[i] = new Object();
+        }
+        int count = 0;
+        for (int i = 0; i < oa.length; i++) {
+            if (oa[i] == null)
+                count += 1;
+        }
+        return count;
+    }
+
+    public static void main() {
+        test4();
+        test3();
+    }
+}
diff --git a/p/ShortArray.java b/p/ShortArray.java
new file mode 100644
index 0000000..5ab5e2e
--- /dev/null
+++ b/p/ShortArray.java
@@ -0,0 +1,17 @@
+package p;
+
+class ShortArray {
+    static short test() {
+        short[] l = new short[10];
+        for (int i = 0; i < l.length; i++)
+            l[i] = (short)(i * 3);
+        short sum = 0;
+        for (int i = 0; i < l.length; i++)
+            sum += l[i];
+        return sum;
+    }
+
+    public static void main() {
+        test();
+    }
+}