Remove use of ArrayStack and rename get(int) to peek(int) which is a better name IMHO.

import-control.xml

@@ -38,7 +38,6 @@
     <allow pkg="java.math"/>
 
     <subpackage name="indentation">
-      <allow class="org.apache.commons.collections.ArrayStack"/>
       <allow pkg="java.lang.reflect"/>
     </subpackage>
 

src/checkstyle/com/puppycrawl/tools/checkstyle/Checker.java

@@ -396,7 +396,7 @@ public class Checker extends AutomaticBean
                 // already contains one
                 sb.append(File.separatorChar);
             }
-            sb.append(s.get(i));
+            sb.append(s.peek(i));
         }
 
 

src/checkstyle/com/puppycrawl/tools/checkstyle/api/FastStack.java

@@ -87,12 +87,13 @@ public class FastStack<E> implements Iterable<E>
     }
 
     /**
-     * Return the element at the specified index.
+     * Return the element at the specified index. It does not remove the
+     * element from the stack.
      * @param aIndex the index to return
      * @return the element at the index
      * @throws IllegalArgumentException if index out of range
      */
-    public E get(int aIndex)
+    public E peek(int aIndex)
     {
         if ((aIndex < 0) || (aIndex >= mEntries.size())) {
             throw new IllegalArgumentException("index out of range.");

src/checkstyle/com/puppycrawl/tools/checkstyle/checks/coding/FinalLocalVariableCheck.java

@@ -185,7 +185,7 @@ public class FinalLocalVariableCheck extends Check
     private void removeVariable(DetailAST aAST)
     {
         for (int i = mScopeStack.size() - 1; i >= 0; i--) {
-            final Map<String, DetailAST> state = mScopeStack.get(i);
+            final Map<String, DetailAST> state = mScopeStack.peek(i);
             final Object obj = state.remove(aAST.getText());
             if (obj != null) {
                 break;

src/checkstyle/com/puppycrawl/tools/checkstyle/checks/indentation/IndentationCheck.java

@@ -20,9 +20,9 @@ package com.puppycrawl.tools.checkstyle.checks.indentation;
 
 import com.puppycrawl.tools.checkstyle.api.Check;
 import com.puppycrawl.tools.checkstyle.api.DetailAST;
+import com.puppycrawl.tools.checkstyle.api.FastStack;
 import com.puppycrawl.tools.checkstyle.api.ScopeUtils;
 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
-import org.apache.commons.collections.ArrayStack;
 
 // TODO: allow preset indentation styles (IE... GNU style, Sun style, etc...)?
 
@@ -122,7 +122,8 @@ public class IndentationCheck extends Check
     private int mBraceAdjustment;
 
     /** handlers currently in use */
-    private final ArrayStack mHandlers = new ArrayStack();
+    private final FastStack<ExpressionHandler> mHandlers =
+        FastStack.newInstance();
 
     /** factory from which handlers are distributed */
     private final HandlerFactory mHandlerFactory = new HandlerFactory();
@@ -241,7 +242,7 @@ public class IndentationCheck extends Check
         }
 
         final ExpressionHandler handler = mHandlerFactory.getHandler(this, aAST,
-            (ExpressionHandler) mHandlers.peek());
+            mHandlers.peek());
         mHandlers.push(handler);
         try {
             handler.checkIndentation();

src/tests/com/puppycrawl/tools/checkstyle/api/FastStackTest.java

@@ -35,7 +35,7 @@ public class FastStackTest
         }
         assertEquals(num, fs.size());
         assertFalse(fs.isEmpty());
-        assertEquals(1, fs.get(1).intValue());
+        assertEquals(1, fs.peek(1).intValue());
         assertEquals(num - 1, fs.peek().intValue());
         assertEquals(num, fs.size());
         for (int i = 0; i < num; i++)