diff --git a/core/src/main/java/hudson/ClassicPluginStrategy.java b/core/src/main/java/hudson/ClassicPluginStrategy.java
index e46014f1a9208589b1d9aa645a7b49d5cac2cd57..58c528474ff484b145c342c4eac05ac97461505d 100644
--- a/core/src/main/java/hudson/ClassicPluginStrategy.java
+++ b/core/src/main/java/hudson/ClassicPluginStrategy.java
@@ -289,7 +289,7 @@ public class ClassicPluginStrategy implements PluginStrategy {
     protected ClassLoader createClassLoader(List<File> paths, ClassLoader parent, Attributes atts) throws IOException {
         if (atts != null) {
             String usePluginFirstClassLoader = atts.getValue( "PluginFirstClassLoader" );
-            if (Boolean.valueOf( usePluginFirstClassLoader )) {
+            if (Boolean.parseBoolean( usePluginFirstClassLoader )) {
                 PluginFirstClassLoader classLoader = new PluginFirstClassLoader();
                 classLoader.setParentFirst( false );
                 classLoader.setParent( parent );
diff --git a/core/src/main/java/hudson/Util.java b/core/src/main/java/hudson/Util.java
index 20539986c3a9ddf912a2358a75700fd5376e2b05..e0009b24536e666eaad495bc25bdf2ee9c6bfbfb 100644
--- a/core/src/main/java/hudson/Util.java
+++ b/core/src/main/java/hudson/Util.java
@@ -905,10 +905,10 @@ public class Util {
                 }
 
                 byte[] bytes = new String(new int[] { codePoint }, 0, 1).getBytes(StandardCharsets.UTF_8);
-                for(int j=0;j<bytes.length;j++) {
+                for (byte aByte : bytes) {
                     out.append('%');
-                    out.append(toDigit((bytes[j] >> 4) & 0xF));
-                    out.append(toDigit(bytes[j] & 0xF));
+                    out.append(toDigit((aByte >> 4) & 0xF));
+                    out.append(toDigit(aByte & 0xF));
                 }
 
                 if(Character.charCount(codePoint) > 1) {
diff --git a/core/src/main/java/hudson/model/BooleanParameterDefinition.java b/core/src/main/java/hudson/model/BooleanParameterDefinition.java
index 15cb4ec80aee93663f490f5f86f1eb974698bce1..5a96b06ec2459263a123050654fa3c01a114262c 100644
--- a/core/src/main/java/hudson/model/BooleanParameterDefinition.java
+++ b/core/src/main/java/hudson/model/BooleanParameterDefinition.java
@@ -65,7 +65,7 @@ public class BooleanParameterDefinition extends SimpleParameterDefinition {
     }
 
     public ParameterValue createValue(String value) {
-        return new BooleanParameterValue(getName(),Boolean.valueOf(value),getDescription());
+        return new BooleanParameterValue(getName(),Boolean.parseBoolean(value),getDescription());
     }
 
     @Override
diff --git a/core/src/main/java/hudson/model/DirectoryBrowserSupport.java b/core/src/main/java/hudson/model/DirectoryBrowserSupport.java
index a69a83e7a3eb680a928bc7a218aaa2d92779999e..679ca34f66acf837d06e2f6fa01be6c28436d2e6 100644
--- a/core/src/main/java/hudson/model/DirectoryBrowserSupport.java
+++ b/core/src/main/java/hudson/model/DirectoryBrowserSupport.java
@@ -181,7 +181,7 @@ public final class DirectoryBrowserSupport implements HttpResponse {
         }
 
         String path = getPath(req);
-        if(path.replace('\\','/').indexOf("/../")!=-1) {
+        if(path.replace('\\', '/').contains("/../")) {
             // don't serve anything other than files in the artifacts dir
             rsp.sendError(HttpServletResponse.SC_BAD_REQUEST);
             return;
diff --git a/core/src/main/java/jenkins/model/Configuration.java b/core/src/main/java/jenkins/model/Configuration.java
index 8b4cea7ac7fa7f257044bc90a76b9dac55faad24..66ca7302c36335a713b3ff0feeb5f4786ed3a602 100644
--- a/core/src/main/java/jenkins/model/Configuration.java
+++ b/core/src/main/java/jenkins/model/Configuration.java
@@ -31,7 +31,7 @@ public class Configuration {
 
     public static boolean getBooleanConfigParameter(String name, boolean defaultValue) {
         String value = getStringConfigParameter(name,null);
-        return (value==null)?defaultValue:Boolean.valueOf(value);
+        return (value==null)?defaultValue:Boolean.parseBoolean(value);
     }
 
     public static String getStringConfigParameter(String name, String defaultValue) {
diff --git a/core/src/main/java/jenkins/security/FrameOptionsPageDecorator.java b/core/src/main/java/jenkins/security/FrameOptionsPageDecorator.java
index eaade662f435a341429f09926613e47416def289..0fb11fa4ede903c183fd46a779534f567582da0f 100644
--- a/core/src/main/java/jenkins/security/FrameOptionsPageDecorator.java
+++ b/core/src/main/java/jenkins/security/FrameOptionsPageDecorator.java
@@ -15,5 +15,5 @@ import org.kohsuke.accmod.restrictions.NoExternalUse;
 @Extension(ordinal = 1000) @Symbol("frameOptions")
 public class FrameOptionsPageDecorator extends PageDecorator {
     @Restricted(NoExternalUse.class)
-    public static boolean enabled = Boolean.valueOf(SystemProperties.getString(FrameOptionsPageDecorator.class.getName() + ".enabled", "true"));
+    public static boolean enabled = Boolean.parseBoolean(SystemProperties.getString(FrameOptionsPageDecorator.class.getName() + ".enabled", "true"));
 }
diff --git a/core/src/main/java/jenkins/util/AntClassLoader.java b/core/src/main/java/jenkins/util/AntClassLoader.java
index 854e3d00992407ab9d2a52423ed5783f1db28f87..7579ce7e0f3d803f78704d7e97f381c2d0cb8a7c 100644
--- a/core/src/main/java/jenkins/util/AntClassLoader.java
+++ b/core/src/main/java/jenkins/util/AntClassLoader.java
@@ -365,9 +365,9 @@ public class AntClassLoader extends ClassLoader implements SubBuildListener {
         if (classpath != null) {
             Path actualClasspath = classpath.concatSystemClasspath("ignore");
             String[] pathElements = actualClasspath.list();
-            for (int i = 0; i < pathElements.length; ++i) {
+            for (String pathElement : pathElements) {
                 try {
-                    addPathElement(pathElements[i]);
+                    addPathElement(pathElement);
                 } catch (BuildException e) {
                     // ignore path elements which are invalid
                     // relative to the project