diff --git a/core/src/main/java/hudson/FilePath.java b/core/src/main/java/hudson/FilePath.java
index 4d75292dce..ea1c06c7d6 100644
--- a/core/src/main/java/hudson/FilePath.java
+++ b/core/src/main/java/hudson/FilePath.java
@@ -3279,7 +3279,7 @@ public final class FilePath implements SerializableOnlyOverRemoting {
         return act(new IsDescendant(potentialChildRelativePath));
     }
 
-    private class IsDescendant extends SecureFileCallable<Boolean> {
+    private static class IsDescendant extends SecureFileCallable<Boolean> {
         private static final long serialVersionUID = 1L;
         private String potentialChildRelativePath;
 
diff --git a/core/src/main/java/hudson/TcpSlaveAgentListener.java b/core/src/main/java/hudson/TcpSlaveAgentListener.java
index 39ba388d2d..dfe9f4ce20 100644
--- a/core/src/main/java/hudson/TcpSlaveAgentListener.java
+++ b/core/src/main/java/hudson/TcpSlaveAgentListener.java
@@ -360,7 +360,7 @@ public final class TcpSlaveAgentListener extends Thread {
     }
 
     // This is essentially just to be able to pass the parent thread into the callback, as it can't access it otherwise
-    private abstract class ConnectionHandlerFailureCallback {
+    private static abstract class ConnectionHandlerFailureCallback {
         private Thread parentThread;
 
         public ConnectionHandlerFailureCallback(Thread parentThread) {
diff --git a/core/src/main/java/hudson/cli/CLIAction.java b/core/src/main/java/hudson/cli/CLIAction.java
index 102dbbc00b..efca422c44 100644
--- a/core/src/main/java/hudson/cli/CLIAction.java
+++ b/core/src/main/java/hudson/cli/CLIAction.java
@@ -190,7 +190,7 @@ public class CLIAction implements UnprotectedRootAction, StaplerProxy {
         }
     }
 
-    class ServerSideImpl extends PlainCLIProtocol.ServerSide {
+    static class ServerSideImpl extends PlainCLIProtocol.ServerSide {
         private Thread runningThread;
         private boolean ready;
         private final List<String> args = new ArrayList<>();
diff --git a/core/src/main/java/hudson/fsp/WorkspaceSnapshotSCM.java b/core/src/main/java/hudson/fsp/WorkspaceSnapshotSCM.java
index e8c19e62a8..426ad5b7e1 100644
--- a/core/src/main/java/hudson/fsp/WorkspaceSnapshotSCM.java
+++ b/core/src/main/java/hudson/fsp/WorkspaceSnapshotSCM.java
@@ -69,7 +69,7 @@ public class WorkspaceSnapshotSCM extends SCM {
     /**
      * {@link Exception} indicating that the resolution of the job/permalink failed.
      */
-    private final class ResolvedFailedException extends Exception {
+    private static final class ResolvedFailedException extends Exception {
         private ResolvedFailedException(String message) {
             super(message);
         }
diff --git a/core/src/main/java/hudson/util/XStream2.java b/core/src/main/java/hudson/util/XStream2.java
index 43f0dfd08c..fb3e4a8431 100644
--- a/core/src/main/java/hudson/util/XStream2.java
+++ b/core/src/main/java/hudson/util/XStream2.java
@@ -327,7 +327,7 @@ public class XStream2 extends XStream {
         mapperInjectionPoint.setDelegate(m);
     }
 
-    final class MapperInjectionPoint extends MapperDelegate {
+    final static class MapperInjectionPoint extends MapperDelegate {
         public MapperInjectionPoint(Mapper wrapped) {
             super(wrapped);
         }
diff --git a/core/src/main/java/jenkins/FilePathFilterAggregator.java b/core/src/main/java/jenkins/FilePathFilterAggregator.java
index 407d8da2cb..f338d25888 100644
--- a/core/src/main/java/jenkins/FilePathFilterAggregator.java
+++ b/core/src/main/java/jenkins/FilePathFilterAggregator.java
@@ -20,7 +20,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
 class FilePathFilterAggregator extends FilePathFilter {
     private final CopyOnWriteArrayList<Entry> all = new CopyOnWriteArrayList<>();
 
-    private class Entry implements Comparable<Entry> {
+    private static class Entry implements Comparable<Entry> {
         final FilePathFilter filter;
         final double ordinal;
 
diff --git a/core/src/test/java/hudson/BulkChangeTest.java b/core/src/test/java/hudson/BulkChangeTest.java
index 7e93dc4e09..e738e9259f 100644
--- a/core/src/test/java/hudson/BulkChangeTest.java
+++ b/core/src/test/java/hudson/BulkChangeTest.java
@@ -37,7 +37,7 @@ import java.io.IOException;
  */
 public class BulkChangeTest {
 
-    private class Point implements Saveable {
+    private static class Point implements Saveable {
         /**
          * Don't actually do any save, but just remember how many the actual I/O would have happened.
          */
diff --git a/core/src/test/java/hudson/model/AbstractItemTest.java b/core/src/test/java/hudson/model/AbstractItemTest.java
index b5dcdf41d2..4ee09dfad0 100644
--- a/core/src/test/java/hudson/model/AbstractItemTest.java
+++ b/core/src/test/java/hudson/model/AbstractItemTest.java
@@ -16,7 +16,7 @@ import org.jvnet.hudson.test.Issue;
 @SuppressWarnings("unchecked")
 public class AbstractItemTest {
 
-    private class StubAbstractItem extends AbstractItem {
+    private static class StubAbstractItem extends AbstractItem {
 
         protected StubAbstractItem() {
             // sending in null as parent as I don't care for my current tests
@@ -91,7 +91,7 @@ public class AbstractItemTest {
         assertEquals(displayName, i.getDisplayName());
     }
 
-    private class NameNotEditableItem extends AbstractItem {
+    private static class NameNotEditableItem extends AbstractItem {
 
         protected NameNotEditableItem(ItemGroup parent, String name){
             super(parent, name);
diff --git a/core/src/test/java/hudson/model/EnvironmentContributingActionTest.java b/core/src/test/java/hudson/model/EnvironmentContributingActionTest.java
index 8bf6c69b30..aee451908a 100644
--- a/core/src/test/java/hudson/model/EnvironmentContributingActionTest.java
+++ b/core/src/test/java/hudson/model/EnvironmentContributingActionTest.java
@@ -11,7 +11,7 @@ import static org.mockito.Mockito.when;
 
 
 public class EnvironmentContributingActionTest {
-    class OverrideRun extends InvisibleAction implements EnvironmentContributingAction {
+    static class OverrideRun extends InvisibleAction implements EnvironmentContributingAction {
         private boolean wasCalled = false;
 
         @Override
@@ -24,7 +24,7 @@ public class EnvironmentContributingActionTest {
         }
     }
 
-    class OverrideAbstractBuild extends InvisibleAction implements EnvironmentContributingAction {
+    static class OverrideAbstractBuild extends InvisibleAction implements EnvironmentContributingAction {
         private boolean wasCalled = false;
 
         @Override
@@ -38,7 +38,7 @@ public class EnvironmentContributingActionTest {
         }
     }
 
-    class OverrideBoth extends InvisibleAction implements EnvironmentContributingAction {
+    static class OverrideBoth extends InvisibleAction implements EnvironmentContributingAction {
         private boolean wasCalledAbstractBuild = false;
         private boolean wasCalledRun = false;
 
diff --git a/core/src/test/java/hudson/model/FingerprintCleanupThreadTest.java b/core/src/test/java/hudson/model/FingerprintCleanupThreadTest.java
index 61a1a72645..549a50df50 100644
--- a/core/src/test/java/hudson/model/FingerprintCleanupThreadTest.java
+++ b/core/src/test/java/hudson/model/FingerprintCleanupThreadTest.java
@@ -107,7 +107,7 @@ public class FingerprintCleanupThreadTest {
         tempDirectory.toFile().deleteOnExit();
     }
 
-    private class TestTaskListener implements TaskListener {
+    private static class TestTaskListener implements TaskListener {
 
         private ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
         private PrintStream logStream = new PrintStream(outputStream);
@@ -126,7 +126,6 @@ public class FingerprintCleanupThreadTest {
 
         public TestFingerprintCleanupThread(Fingerprint fingerprintToLoad) throws IOException {
             this.fingerprintToLoad = fingerprintToLoad;
-            return;
         }
 
         @Override
@@ -146,7 +145,7 @@ public class FingerprintCleanupThreadTest {
 
     }
 
-    private class TestFingerprint extends Fingerprint {
+    private static class TestFingerprint extends Fingerprint {
 
         private boolean isAlive = true;
 
diff --git a/core/src/test/java/hudson/model/LoadStatisticsTest.java b/core/src/test/java/hudson/model/LoadStatisticsTest.java
index 246bdb3f1d..d49fad2609 100644
--- a/core/src/test/java/hudson/model/LoadStatisticsTest.java
+++ b/core/src/test/java/hudson/model/LoadStatisticsTest.java
@@ -101,7 +101,7 @@ public class LoadStatisticsTest {
         assertThat(LoadStatistics.isModern(LoadStatistics.class), is(false));
     }
 
-    private class Modern extends LoadStatistics {
+    private static class Modern extends LoadStatistics {
 
         protected Modern(int initialOnlineExecutors, int initialBusyExecutors) {
             super(initialOnlineExecutors, initialBusyExecutors);
diff --git a/core/src/test/java/hudson/util/CyclicGraphDetectorTest.java b/core/src/test/java/hudson/util/CyclicGraphDetectorTest.java
index d99640068b..42c68e0e27 100644
--- a/core/src/test/java/hudson/util/CyclicGraphDetectorTest.java
+++ b/core/src/test/java/hudson/util/CyclicGraphDetectorTest.java
@@ -16,7 +16,7 @@ import java.util.Set;
  */
 public class CyclicGraphDetectorTest {
 
-    private class Edge {
+    private static class Edge {
         String src,dst;
 
         private Edge(String src, String dst) {
@@ -25,7 +25,7 @@ public class CyclicGraphDetectorTest {
         }
     }
 
-    private class Graph extends ArrayList<Edge> {
+    private static class Graph extends ArrayList<Edge> {
         Graph e(String src, String dst) {
             add(new Edge(src,dst));
             return this;
diff --git a/core/src/test/java/hudson/util/IsOverriddenTest.java b/core/src/test/java/hudson/util/IsOverriddenTest.java
index 36f45c3de5..0048a69553 100644
--- a/core/src/test/java/hudson/util/IsOverriddenTest.java
+++ b/core/src/test/java/hudson/util/IsOverriddenTest.java
@@ -62,7 +62,7 @@ public class IsOverriddenTest {
         Util.isOverridden(Base.class, Intermediate.class, "aPrivateMethod");
     }
 
-    public abstract class Base<T> {
+    public static abstract class Base<T> {
         protected abstract void method();
         private void aPrivateMethod() {}
         public void setX(T t) {}
diff --git a/core/src/test/java/hudson/util/io/TarArchiverTest.java b/core/src/test/java/hudson/util/io/TarArchiverTest.java
index 8900f83193..0983d9a199 100644
--- a/core/src/test/java/hudson/util/io/TarArchiverTest.java
+++ b/core/src/test/java/hudson/util/io/TarArchiverTest.java
@@ -136,7 +136,7 @@ public class TarArchiverTest {
         t1.join();
     }
 
-    private class GrowingFileRunnable implements Runnable {
+    private static class GrowingFileRunnable implements Runnable {
         private boolean finish = false;
         private Exception ex = null;
         private File file;
diff --git a/core/src/test/java/jenkins/util/MarkFindingOutputStreamTest.java b/core/src/test/java/jenkins/util/MarkFindingOutputStreamTest.java
index 3de38b3449..19e18af62b 100644
--- a/core/src/test/java/jenkins/util/MarkFindingOutputStreamTest.java
+++ b/core/src/test/java/jenkins/util/MarkFindingOutputStreamTest.java
@@ -84,7 +84,7 @@ public class MarkFindingOutputStreamTest {
             m.write(s.charAt(i));
     }
 
-    class MarkCountingOutputStream extends MarkFindingOutputStream {
+    static class MarkCountingOutputStream extends MarkFindingOutputStream {
         int count = 0;
 
         MarkCountingOutputStream(OutputStream base) {
diff --git a/test/src/test/java/hudson/ExtensionListListenerTest.java b/test/src/test/java/hudson/ExtensionListListenerTest.java
index b3449dbeb9..3a6088e50d 100644
--- a/test/src/test/java/hudson/ExtensionListListenerTest.java
+++ b/test/src/test/java/hudson/ExtensionListListenerTest.java
@@ -56,7 +56,7 @@ public class ExtensionListListenerTest {
         Assert.assertEquals(1, listListener.onChangeCallCount);
     }
 
-    private class MyExtensionListListener extends ExtensionListListener {
+    private static class MyExtensionListListener extends ExtensionListListener {
         private int onChangeCallCount = 0;
         @Override
         public void onChange() {
diff --git a/test/src/test/java/hudson/model/ApiSEC1704Test.java b/test/src/test/java/hudson/model/ApiSEC1704Test.java
index e0a8bcf4b6..3aca1048b5 100644
--- a/test/src/test/java/hudson/model/ApiSEC1704Test.java
+++ b/test/src/test/java/hudson/model/ApiSEC1704Test.java
@@ -99,7 +99,7 @@ public class ApiSEC1704Test {
         }
 
         @ExportedBean
-        class CustomData {
+        static class CustomData {
             private String secret;
             CustomData(String secret){
                 this.secret = secret;
diff --git a/test/src/test/java/hudson/model/UpdateCenterConnectionStatusTest.java b/test/src/test/java/hudson/model/UpdateCenterConnectionStatusTest.java
index b06ee59627..50c2eb69a9 100644
--- a/test/src/test/java/hudson/model/UpdateCenterConnectionStatusTest.java
+++ b/test/src/test/java/hudson/model/UpdateCenterConnectionStatusTest.java
@@ -124,7 +124,7 @@ public class UpdateCenterConnectionStatusTest {
         Assert.assertEquals(ConnectionStatus.FAILED, job.connectionStates.get(ConnectionStatus.UPDATE_SITE));
     }
 
-    private class TestConfig extends UpdateCenter.UpdateCenterConfiguration {
+    private static class TestConfig extends UpdateCenter.UpdateCenterConfiguration {
 
         private IOException checkConnectionException;
         private IOException checkUpdateCenterException;
diff --git a/test/src/test/java/hudson/security/SecurityRealmTest.java b/test/src/test/java/hudson/security/SecurityRealmTest.java
index 5d4ef3868f..da4f4a05e7 100644
--- a/test/src/test/java/hudson/security/SecurityRealmTest.java
+++ b/test/src/test/java/hudson/security/SecurityRealmTest.java
@@ -72,7 +72,7 @@ public class SecurityRealmTest {
         assertThat(response.getResponseHeaderValue("Expires"), is("0"));
     }
 
-    private class DummyCaptcha extends CaptchaSupport {
+    private static class DummyCaptcha extends CaptchaSupport {
         @Override
         public boolean validateCaptcha(String id, String text) {
             return false;
diff --git a/test/src/test/java/hudson/security/WhoAmITest.java b/test/src/test/java/hudson/security/WhoAmITest.java
index b59bc98cbc..e74e07ccf2 100644
--- a/test/src/test/java/hudson/security/WhoAmITest.java
+++ b/test/src/test/java/hudson/security/WhoAmITest.java
@@ -201,7 +201,7 @@ public class WhoAmITest {
         )));
     }
 
-    private class SecurityRealmImpl extends AbstractPasswordBasedSecurityRealm {
+    private static class SecurityRealmImpl extends AbstractPasswordBasedSecurityRealm {
 
         @Override
         protected UserDetails authenticate(String username, String password) throws AuthenticationException {
diff --git a/test/src/test/java/hudson/tools/ZipExtractionInstallerTest.java b/test/src/test/java/hudson/tools/ZipExtractionInstallerTest.java
index 22a211ddfd..75f41e5d6e 100644
--- a/test/src/test/java/hudson/tools/ZipExtractionInstallerTest.java
+++ b/test/src/test/java/hudson/tools/ZipExtractionInstallerTest.java
@@ -136,7 +136,7 @@ public class ZipExtractionInstallerTest {
         assertThat(lastRequest.getResponseText(), containsString(Messages.ZipExtractionInstaller_malformed_url()));
     }
     
-    private class SpyingJavaScriptEngine extends JavaScriptEngine {
+    private static class SpyingJavaScriptEngine extends JavaScriptEngine {
         private List<XMLHttpRequest> storedRequests = new ArrayList<>();
         private String urlToMatch;
         private HttpMethod method;
diff --git a/test/src/test/java/jenkins/security/stapler/DoActionFilterTest.java b/test/src/test/java/jenkins/security/stapler/DoActionFilterTest.java
index ed5bafdfca..d59bed0d8a 100644
--- a/test/src/test/java/jenkins/security/stapler/DoActionFilterTest.java
+++ b/test/src/test/java/jenkins/security/stapler/DoActionFilterTest.java
@@ -73,7 +73,7 @@ public class DoActionFilterTest extends StaplerAbstractTest {
         
         private TestAccessModifier getPrivate() {return new TestAccessModifier();}
         
-        public class TestAccessModifier {
+        public static class TestAccessModifier {
             @GET
             public String doValue() {
                 return "hello";