diff --git a/src/hotspot/os/aix/os_aix.cpp b/src/hotspot/os/aix/os_aix.cpp
index 842ab0c6eebd6..44b9571e1024c 100644
--- a/src/hotspot/os/aix/os_aix.cpp
+++ b/src/hotspot/os/aix/os_aix.cpp
@@ -468,7 +468,7 @@ static void query_multipage_support() {
 
     // Can we use mmap with 64K pages? (Should be available with AIX7.3 TL1)
     {
-      void* p = mmap(NULL, 64*K, PROT_READ | PROT_WRITE, MAP_ANON_64K | MAP_ANONYMOUS | MAP_SHARED, -1, 0);
+      void* p = mmap(nullptr, 64*K, PROT_READ | PROT_WRITE, MAP_ANON_64K | MAP_ANONYMOUS | MAP_SHARED, -1, 0);
       assert(p != (void*) -1, "mmap failed");
       if (p != (void*) -1) {
         g_multipage_support.can_use_64K_mmap_pages = (64*K == os::Aix::query_pagesize(p));
diff --git a/src/hotspot/os/linux/cgroupSubsystem_linux.cpp b/src/hotspot/os/linux/cgroupSubsystem_linux.cpp
index d51499611a8d1..4a8fda432d894 100644
--- a/src/hotspot/os/linux/cgroupSubsystem_linux.cpp
+++ b/src/hotspot/os/linux/cgroupSubsystem_linux.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -167,7 +167,7 @@ static bool find_ro_opt(char* mount_opts) {
   char* token;
   char* mo_ptr = mount_opts;
   // mount options are comma-separated (man proc).
-  while ((token = strsep(&mo_ptr, ",")) != NULL) {
+  while ((token = strsep(&mo_ptr, ",")) != nullptr) {
     if (strcmp(token, "ro") == 0) {
       return true;
     }
diff --git a/src/hotspot/os/posix/os_posix.cpp b/src/hotspot/os/posix/os_posix.cpp
index 75253843593c6..df11832ae95c8 100644
--- a/src/hotspot/os/posix/os_posix.cpp
+++ b/src/hotspot/os/posix/os_posix.cpp
@@ -816,7 +816,7 @@ void* os::dll_lookup(void* handle, const char* name) {
   void* ret = ::dlsym(handle, name);
   if (ret == nullptr) {
     const char* tmp = ::dlerror();
-    // It is possible that we found a NULL symbol, hence no error.
+    // It is possible that we found a null symbol, hence no error.
     if (tmp != nullptr) {
       log_debug(os)("Symbol %s not found in dll: %s", name, tmp);
     }
diff --git a/src/hotspot/os/windows/os_windows.cpp b/src/hotspot/os/windows/os_windows.cpp
index 4dafef0c09823..40a022bbc174d 100644
--- a/src/hotspot/os/windows/os_windows.cpp
+++ b/src/hotspot/os/windows/os_windows.cpp
@@ -4150,7 +4150,7 @@ void getWindowsInstallationType(char* buffer, int bufferSize) {
   }
 
   // Query the value
-  if (RegQueryValueExA(hKey, valueName, NULL, NULL, (LPBYTE)buffer, &valueLength) != ERROR_SUCCESS) {
+  if (RegQueryValueExA(hKey, valueName, nullptr, nullptr, (LPBYTE)buffer, &valueLength) != ERROR_SUCCESS) {
     RegCloseKey(hKey);
     buffer[0] = '\0';
     return;
diff --git a/src/hotspot/share/classfile/classLoader.cpp b/src/hotspot/share/classfile/classLoader.cpp
index 9a68e2640443f..cb155bdeb1939 100644
--- a/src/hotspot/share/classfile/classLoader.cpp
+++ b/src/hotspot/share/classfile/classLoader.cpp
@@ -1242,7 +1242,7 @@ static char decode_percent_encoded(const char *str, size_t& index) {
     hex[1] = str[index + 2];
     hex[2] = '\0';
     index += 2;
-    return (char) strtol(hex, NULL, 16);
+    return (char) strtol(hex, nullptr, 16);
   }
   return str[index];
 }
diff --git a/src/hotspot/share/include/cds.h b/src/hotspot/share/include/cds.h
index af48c1a8c3554..4cc309dd9913d 100644
--- a/src/hotspot/share/include/cds.h
+++ b/src/hotspot/share/include/cds.h
@@ -69,7 +69,7 @@ typedef struct CDSFileMapRegion {
   size_t  _ptrmap_offset;     // Bitmap for relocating native pointer fields in archived heap objects.
                               // (The base address is the bottom of the BM region).
   size_t  _ptrmap_size_in_bits;
-  char*   _mapped_base;       // Actually mapped address (NULL if this region is not mapped).
+  char*   _mapped_base;       // Actually mapped address (null if this region is not mapped).
 } CDSFileMapRegion;
 
 // This portion of the archive file header must remain unchanged for
diff --git a/src/hotspot/share/include/jvm.h b/src/hotspot/share/include/jvm.h
index 6634306636b15..23040aa1dcd45 100644
--- a/src/hotspot/share/include/jvm.h
+++ b/src/hotspot/share/include/jvm.h
@@ -419,7 +419,7 @@ JVM_FindPrimitiveClass(JNIEnv *env, const char *utf);
 
 
 /*
- * Find a class from a boot class loader. Returns NULL if class not found.
+ * Find a class from a boot class loader. Returns null if class not found.
  */
 JNIEXPORT jclass JNICALL
 JVM_FindClassFromBootLoader(JNIEnv *env, const char *name);
diff --git a/src/hotspot/share/oops/constantPool.cpp b/src/hotspot/share/oops/constantPool.cpp
index 1c295e10b21db..7147e2588c965 100644
--- a/src/hotspot/share/oops/constantPool.cpp
+++ b/src/hotspot/share/oops/constantPool.cpp
@@ -477,7 +477,7 @@ void ConstantPool::remove_resolved_klass_if_non_deterministic(int cp_index) {
   if (k == nullptr) {
     // We'd come here if the referenced class has been excluded via
     // SystemDictionaryShared::is_excluded_class(). As a result, ArchiveBuilder
-    // has cleared the resolved_klasses()->at(...) pointer to NULL. Thus, we
+    // has cleared the resolved_klasses()->at(...) pointer to null. Thus, we
     // need to revert the tag to JVM_CONSTANT_UnresolvedClass.
     can_archive = false;
   } else {
diff --git a/src/hotspot/share/opto/escape.cpp b/src/hotspot/share/opto/escape.cpp
index f8a0209d9ad15..d16f778ea8462 100644
--- a/src/hotspot/share/opto/escape.cpp
+++ b/src/hotspot/share/opto/escape.cpp
@@ -644,7 +644,7 @@ bool ConnectionGraph::can_reduce_phi(PhiNode* ophi) const {
 //
 // 'curr_ctrl' is the control of the CastPP that we want to split through phi.
 // If the CastPP currently doesn't have a control then the CmpP/N will be
-// against the NULL constant, otherwise it will be against the constant input of
+// against the null constant, otherwise it will be against the constant input of
 // the existing CmpP/N. It's guaranteed that there will be a CmpP/N in the later
 // case because we have constraints on it and because the CastPP has a control
 // input.
@@ -672,7 +672,7 @@ Node* ConnectionGraph::specialize_cmp(Node* base, Node* curr_ctrl) {
 // means that the CastPP now will be specific for a given base instead of a Phi.
 // An If-Then-Else-Region block is inserted to control the CastPP. The control
 // of the CastPP is a copy of the current one (if there is one) or a check
-// against NULL.
+// against null.
 //
 // Before:
 //
@@ -806,10 +806,10 @@ Node* ConnectionGraph::split_castpp_load_through_phi(Node* curr_addp, Node* curr
 // After splitting the CastPP we'll put it under an If-Then-Else-Region control
 // flow. If the CastPP originally had an IfTrue/False control input then we'll
 // use a similar CmpP/N to control the new If-Then-Else-Region. Otherwise, we'll
-// juse use a CmpP/N against the NULL constant.
+// juse use a CmpP/N against the null constant.
 //
 // The If-Then-Else-Region isn't always needed. For instance, if input to
-// splitted cast was not nullable (or if it was the NULL constant) then we don't
+// splitted cast was not nullable (or if it was the null constant) then we don't
 // need (shouldn't) use a CastPP at all.
 //
 // After the casts are splitted we'll split the AddP->Loads through the Phi and
@@ -837,7 +837,7 @@ Node* ConnectionGraph::split_castpp_load_through_phi(Node* curr_addp, Node* curr
 //
 // After (Very much simplified):
 //
-//                         Call  NULL
+//                         Call  Null
 //                            \  /
 //                            CmpP
 //                             |
@@ -873,7 +873,7 @@ void ConnectionGraph::reduce_phi_on_castpp_field_load(Node* curr_castpp, Growabl
   // array, depending on the nullability status of the corresponding input in
   // ophi.
   //
-  //  - nullptr:    Meaning that the base is actually the NULL constant and therefore
+  //  - nullptr:    Meaning that the base is actually the null constant and therefore
   //                we won't try to load from it.
   //
   //  - CFG Node:   Meaning that the base is a CastPP that was specialized for
@@ -890,7 +890,7 @@ void ConnectionGraph::reduce_phi_on_castpp_field_load(Node* curr_castpp, Growabl
 
     if (base_t->maybe_null()) {
       if (base->is_Con()) {
-        // Nothing todo as bases_for_loads[i] is already nullptr
+        // Nothing todo as bases_for_loads[i] is already null
       } else {
         Node* new_castpp = specialize_castpp(curr_castpp, base, ophi->in(0)->in(i));
         bases_for_loads.at_put(i, new_castpp->in(0)); // Use the ctrl of the new node just as a flag
diff --git a/src/hotspot/share/opto/library_call.cpp b/src/hotspot/share/opto/library_call.cpp
index 523b1efd0c243..e3cd60e6d918a 100644
--- a/src/hotspot/share/opto/library_call.cpp
+++ b/src/hotspot/share/opto/library_call.cpp
@@ -7750,11 +7750,11 @@ bool LibraryCallKit::inline_intpoly_montgomeryMult_P256() {
   r = must_be_not_null(r, true);
 
   Node* a_start = array_element_address(a, intcon(0), T_LONG);
-  assert(a_start, "a array is NULL");
+  assert(a_start, "a array is null");
   Node* b_start = array_element_address(b, intcon(0), T_LONG);
-  assert(b_start, "b array is NULL");
+  assert(b_start, "b array is null");
   Node* r_start = array_element_address(r, intcon(0), T_LONG);
-  assert(r_start, "r array is NULL");
+  assert(r_start, "r array is null");
 
   Node* call = make_runtime_call(RC_LEAF | RC_NO_FP,
                                  OptoRuntime::intpoly_montgomeryMult_P256_Type(),
@@ -7779,9 +7779,9 @@ bool LibraryCallKit::inline_intpoly_assign() {
   b = must_be_not_null(b, true);
 
   Node* a_start = array_element_address(a, intcon(0), T_LONG);
-  assert(a_start, "a array is NULL");
+  assert(a_start, "a array is null");
   Node* b_start = array_element_address(b, intcon(0), T_LONG);
-  assert(b_start, "b array is NULL");
+  assert(b_start, "b array is null");
 
   Node* call = make_runtime_call(RC_LEAF | RC_NO_FP,
                                  OptoRuntime::intpoly_assign_Type(),
diff --git a/src/hotspot/share/services/diagnosticFramework.cpp b/src/hotspot/share/services/diagnosticFramework.cpp
index 73aa80a950f93..16f074c9cb503 100644
--- a/src/hotspot/share/services/diagnosticFramework.cpp
+++ b/src/hotspot/share/services/diagnosticFramework.cpp
@@ -424,7 +424,7 @@ bool DCmd::reorder_help_cmd(CmdLine line, stringStream &updated_line) {
   args.print("%s", line.args_addr());
   char* rest = args.as_string();
   char* token = strtok_r(rest, " ", &rest);
-  while (token != NULL) {
+  while (token != nullptr) {
     if (strcmp(token, "-h") == 0 || strcmp(token, "--help") == 0 ||
         strcmp(token, "-help") == 0) {
       updated_line.print("%s", "help ");
diff --git a/test/hotspot/jtreg/serviceability/jvmti/GetMethodDeclaringClass/libTestUnloadedClass.cpp b/test/hotspot/jtreg/serviceability/jvmti/GetMethodDeclaringClass/libTestUnloadedClass.cpp
index c32b787d57894..ad7708ba55d02 100644
--- a/test/hotspot/jtreg/serviceability/jvmti/GetMethodDeclaringClass/libTestUnloadedClass.cpp
+++ b/test/hotspot/jtreg/serviceability/jvmti/GetMethodDeclaringClass/libTestUnloadedClass.cpp
@@ -39,9 +39,9 @@ static std::atomic<jmethodID> ring_buffer[BUFFER_SIZE];
 
 void get_method_details(jmethodID method) {
   jclass method_class;
-  char *class_name = NULL;
+  char *class_name = nullptr;
   if (_jvmti->GetMethodDeclaringClass(method, &method_class) == JVMTI_ERROR_NONE) {
-    if (_jvmti->GetClassSignature(method_class, &class_name, NULL) == JVMTI_ERROR_NONE) {
+    if (_jvmti->GetClassSignature(method_class, &class_name, nullptr) == JVMTI_ERROR_NONE) {
       _jvmti->Deallocate((unsigned char *)class_name);
     }
   }
@@ -49,14 +49,14 @@ void get_method_details(jmethodID method) {
 
 void* read_ringbuffer(void* arg) {
   JNIEnv *env;
-  _jvm->AttachCurrentThreadAsDaemon((void **)&env, NULL);
+  _jvm->AttachCurrentThreadAsDaemon((void **)&env, nullptr);
   for (;;) {
     jmethodID id = ring_buffer[rand() % BUFFER_SIZE].load(std::memory_order_relaxed);
     if (id != (jmethodID)0) {
       get_method_details(id);
     }
   }
-  return NULL;
+  return nullptr;
 }
 
 static void JNICALL ClassPrepareCallback(jvmtiEnv *jvmti_env,
@@ -66,8 +66,8 @@ static void JNICALL ClassPrepareCallback(jvmtiEnv *jvmti_env,
   static bool reader_created = false;
   static int ring_buffer_idx = 0;
 
-  char *class_name = NULL;
-  if (jvmti_env->GetClassSignature(klass, &class_name, NULL) != JVMTI_ERROR_NONE) {
+  char *class_name = nullptr;
+  if (jvmti_env->GetClassSignature(klass, &class_name, nullptr) != JVMTI_ERROR_NONE) {
     return;
   }
   // We only care MyClass and only one thread loads it
@@ -79,7 +79,7 @@ static void JNICALL ClassPrepareCallback(jvmtiEnv *jvmti_env,
 
   if (!reader_created) {
     pthread_t tid;
-    pthread_create(&tid, NULL, read_ringbuffer, NULL);
+    pthread_create(&tid, nullptr, read_ringbuffer, nullptr);
     reader_created = true;
   }
 
@@ -119,7 +119,7 @@ JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *jvm, char *options, void *reserved)
   }
 
   // Enable the ClassPrepare event
-  error = _jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_CLASS_PREPARE, NULL);
+  error = _jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_CLASS_PREPARE, nullptr);
   if (error != JVMTI_ERROR_NONE) {
     fprintf(stderr, "Error enabling ClassPrepare event: %d\n", error);
     return JNI_ERR;
diff --git a/test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/libVThreadEventTest.cpp b/test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/libVThreadEventTest.cpp
index c97a8ef3471aa..13ff93de9dc25 100644
--- a/test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/libVThreadEventTest.cpp
+++ b/test/hotspot/jtreg/serviceability/jvmti/vthread/VThreadEventTest/libVThreadEventTest.cpp
@@ -118,13 +118,13 @@ Agent_OnAttach(JavaVM *vm, char *options, void *reserved) {
   }
 
   clazz = env->FindClass("VThreadEventTest");
-  if (clazz == NULL) {
+  if (clazz == nullptr) {
       LOG("FindClass failed\n");
       return JNI_ERR;
   }
 
   mid = env->GetStaticMethodID(clazz, "agentStarted", "()V");
-  if (mid == NULL) {
+  if (mid == nullptr) {
       LOG("GetStaticMethodID failed\n");
       return JNI_ERR;
   }