diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/freemarker/AbstractFreeMarkerConfiguration.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/freemarker/AbstractFreeMarkerConfiguration.java
index 25b977306e77..fa9c4d50ca63 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/freemarker/AbstractFreeMarkerConfiguration.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/freemarker/AbstractFreeMarkerConfiguration.java
@@ -25,7 +25,7 @@
  *
  * @author Brian Clozel
  */
-class AbstractFreeMarkerConfiguration {
+abstract class AbstractFreeMarkerConfiguration {
 
 	private final FreeMarkerProperties properties;
 
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/AbstractSessionCondition.java b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/AbstractSessionCondition.java
index dc8378c41865..e8ba662cb23a 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/AbstractSessionCondition.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/AbstractSessionCondition.java
@@ -35,7 +35,7 @@
  * @author Madhura Bhave
  * @author Andy Wilkinson
  */
-class AbstractSessionCondition extends SpringBootCondition {
+abstract class AbstractSessionCondition extends SpringBootCondition {
 
 	private final WebApplicationType webApplicationType;
 
diff --git a/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestEmbeddedReactiveWebEnvironmentTests.java b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestEmbeddedReactiveWebEnvironmentTests.java
index 399db3206ea3..501fbb49d838 100644
--- a/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestEmbeddedReactiveWebEnvironmentTests.java
+++ b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestEmbeddedReactiveWebEnvironmentTests.java
@@ -88,7 +88,7 @@ public void annotationAttributesOverridePropertiesFile() throws Exception {
 		assertThat(this.value).isEqualTo(123);
 	}
 
-	protected static class AbstractConfig {
+	protected static abstract class AbstractConfig {
 
 		@Value("${server.port:8080}")
 		private int port = 8080;
diff --git a/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestWebServerWebEnvironmentTests.java b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestWebServerWebEnvironmentTests.java
index 11f95f7bd288..003100031d17 100644
--- a/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestWebServerWebEnvironmentTests.java
+++ b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/AbstractSpringBootTestWebServerWebEnvironmentTests.java
@@ -92,7 +92,7 @@ public void validateWebApplicationContextIsSet() {
 				WebApplicationContextUtils.getWebApplicationContext(this.servletContext));
 	}
 
-	protected static class AbstractConfig {
+	protected static abstract class AbstractConfig {
 
 		@Value("${server.port:8080}")
 		private int port = 8080;
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/AbstractExecutableArchiveLauncherTests.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/AbstractExecutableArchiveLauncherTests.java
index 6bace570ad98..6810605b63f7 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/AbstractExecutableArchiveLauncherTests.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/AbstractExecutableArchiveLauncherTests.java
@@ -43,7 +43,7 @@
  *
  * @author Andy Wilkinson
  */
-public class AbstractExecutableArchiveLauncherTests {
+public abstract class AbstractExecutableArchiveLauncherTests {
 
 	@Rule
 	public TemporaryFolder temp = new TemporaryFolder();
diff --git a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/server/AbstractConfigurableWebServerFactory.java b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/server/AbstractConfigurableWebServerFactory.java
index 82523bb7b641..2b5a32a54dcd 100644
--- a/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/server/AbstractConfigurableWebServerFactory.java
+++ b/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/server/AbstractConfigurableWebServerFactory.java
@@ -37,7 +37,7 @@
  * @author Brian Clozel
  * @since 2.0.0
  */
-public class AbstractConfigurableWebServerFactory
+public abstract class AbstractConfigurableWebServerFactory
 		implements ConfigurableWebServerFactory {
 
 	private int port = 8080;
diff --git a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java
index cafa281cba94..37a0c96d716b 100644
--- a/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java
+++ b/spring-boot-project/spring-boot/src/test/java/org/springframework/boot/SpringApplicationTests.java
@@ -1277,7 +1277,7 @@ static class RefreshFailureException extends RuntimeException {
 
 	}
 
-	static class AbstractTestRunner implements ApplicationContextAware, Ordered {
+	static abstract class AbstractTestRunner implements ApplicationContextAware, Ordered {
 
 		private final String[] expectedBefore;