diff --git a/src/main/java/org/jboss/netty/util/MapUtil.java b/src/main/java/org/jboss/netty/util/MapUtil.java
index 42a476501c..409ca2c165 100644
--- a/src/main/java/org/jboss/netty/util/MapUtil.java
+++ b/src/main/java/org/jboss/netty/util/MapUtil.java
@@ -33,16 +33,21 @@ import org.jboss.netty.logging.InternalLogger;
 import org.jboss.netty.logging.InternalLoggerFactory;
 
 /**
+ * A set of utility methods related with a {@link Map}.
+ *
  * @author The Netty Project (netty-dev@lists.jboss.org)
  * @author Trustin Lee (tlee@redhat.com)
  *
  * @version $Rev$, $Date$
- *
  */
 public class MapUtil {
     private static final InternalLogger logger =
         InternalLoggerFactory.getInstance(MapUtil.class);
 
+    /**
+     * Returns {@code true} if and only if the specified {@code map} is an
+     * ordered map, like {@link LinkedHashMap} is.
+     */
     @SuppressWarnings("unchecked")
     public static boolean isOrderedMap(Map<?, ?> map) {
         Class<?> mapType = map.getClass();
diff --git a/src/main/java/org/jboss/netty/util/StackTraceSimplifier.java b/src/main/java/org/jboss/netty/util/StackTraceSimplifier.java
index 2e0768ee28..db365dfd4b 100644
--- a/src/main/java/org/jboss/netty/util/StackTraceSimplifier.java
+++ b/src/main/java/org/jboss/netty/util/StackTraceSimplifier.java
@@ -26,7 +26,14 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.regex.Pattern;
 
+import org.jboss.netty.channel.DefaultChannelPipeline;
+import org.jboss.netty.channel.SimpleChannelHandler;
+
 /**
+ * Simplifies an exception stack trace by removing unnecessary
+ * {@link StackTraceElement}s.  Please note that the stack trace simplification
+ * is disabled if {@linkplain DebugUtil debug mode} is turned on.
+ *
  * @author The Netty Project (netty-dev@lists.jboss.org)
  * @author Trustin Lee (tlee@redhat.com)
  *
@@ -42,6 +49,11 @@ public class StackTraceSimplifier {
                 "(util\\.(ThreadRenamingRunnable)" +
                 "|channel\\.(SimpleChannelHandler|DefaultChannelPipeline.*))$");
 
+    /**
+     * Removes unnecessary {@link StackTraceElement}s from the specified
+     * exception. {@link ThreadRenamingRunnable}, {@link SimpleChannelHandler},
+     * and {@link DefaultChannelPipeline} will be dropped from the trace.
+     */
     public static void simplify(Throwable e) {
         if (!SIMPLIFY_STACK_TRACE) {
             return;
diff --git a/src/main/java/org/jboss/netty/util/SystemPropertyUtil.java b/src/main/java/org/jboss/netty/util/SystemPropertyUtil.java
index 6ca5fec69f..4e889bfc72 100644
--- a/src/main/java/org/jboss/netty/util/SystemPropertyUtil.java
+++ b/src/main/java/org/jboss/netty/util/SystemPropertyUtil.java
@@ -23,6 +23,8 @@
 package org.jboss.netty.util;
 
 /**
+ * Accesses the system property swallowing a {@link SecurityException}.
+ *
  * @author The Netty Project (netty-dev@lists.jboss.org)
  * @author Trustin Lee (tlee@redhat.com)
  *
@@ -31,6 +33,14 @@ package org.jboss.netty.util;
  */
 public class SystemPropertyUtil {
 
+    /**
+     * Returns the value of the Java system property with the specified
+     * {@code key}.
+     *
+     * @return the property value.
+     *         {@code null} if there's no such property or if an access to the
+     *         specified property is not allowed.
+     */
     public static String get(String key) {
         try {
             return System.getProperty(key);
@@ -39,6 +49,15 @@ public class SystemPropertyUtil {
         }
     }
 
+    /**
+     * Returns the value of the Java system property with the specified
+     * {@code key}, while falling back to the specified default value if
+     * the property access fails.
+     *
+     * @return the property value.
+     *         {@code def} if there's no such property or if an access to the
+     *         specified property is not allowed.
+     */
     public static String get(String key, String def) {
         String value = get(key);
         if (value == null) {