check for redundant modifier

src/checkstyle/com/puppycrawl/tools/checkstyle/checks/RedundantModifierCheck.java

@@ -0,0 +1,85 @@
+package com.puppycrawl.tools.checkstyle.checks;
+
+import java.util.Stack;
+
+import com.puppycrawl.tools.checkstyle.api.Check;
+import com.puppycrawl.tools.checkstyle.api.DetailAST;
+import com.puppycrawl.tools.checkstyle.JavaTokenTypes;
+
+public class RedundantModifierCheck extends Check implements JavaTokenTypes
+{
+    private final Stack mInInterface = new Stack();
+
+    public void beginTree()
+    {
+        super.beginTree();
+        mInInterface.clear();
+    }
+
+    public int[] getDefaultTokens()
+    {
+        return new int[] {MODIFIERS, INTERFACE_DEF, CLASS_DEF};
+    }
+
+    public void visitToken(DetailAST aAST)
+    {
+        switch (aAST.getType())
+        {
+            case INTERFACE_DEF:
+                mInInterface.push(Boolean.TRUE);
+                break;
+            case CLASS_DEF:
+                mInInterface.push(Boolean.FALSE);
+                break;
+            case MODIFIERS:
+
+                // modifiers of the interface itself (public interface X)
+                // will be below the INTERFACE_DEF node. Example:
+
+                // public interface X {void y();}
+
+                // INTERFACE_DEF
+                // + MODUFIERS
+                //   + public
+                // + OBJ_BLOCK
+                //   + ...
+
+                if (inInterfaceBlock(aAST)) {
+                    DetailAST ast = (DetailAST) aAST.getFirstChild();
+                    while (ast != null) {
+                        String modifier = ast.getText();
+                        if ("public".equals(modifier)
+                                || "abstract".equals(modifier))
+                        {
+                            log(ast.getLineNo(),
+                                    ast.getColumnNo(),
+                                    "redundantModifier",
+                                    new String[] {modifier});
+                        }
+                        ast = (DetailAST) ast.getNextSibling();
+                    }
+                }
+                break;
+            default:
+                return;
+        }
+    }
+
+    /** @return whether currently in an interface block,
+     *          i.e. in an OBJ_BLOCK of an INTERFACE_DEF
+     */
+    private boolean inInterfaceBlock(DetailAST aAST)
+    {
+        if (mInInterface.empty()) {
+            return false;
+        }
+        if (aAST.getParent().getType() == INTERFACE_DEF) {
+            int size = mInInterface.size();
+            return size > 1 && Boolean.TRUE.equals(mInInterface.get(size - 2));
+        }
+        else {
+            return Boolean.TRUE.equals(mInInterface.peek());
+        }
+    }
+
+}

src/tests/com/puppycrawl/tools/checkstyle/RedundantModifierTest.java

@@ -0,0 +1,32 @@
+package com.puppycrawl.tools.checkstyle;
+
+import com.puppycrawl.tools.checkstyle.api.LocalizedMessages;
+import com.puppycrawl.tools.checkstyle.api.Check;
+import com.puppycrawl.tools.checkstyle.checks.RedundantModifierCheck;
+
+public class RedundantModifierTest extends AbstractCheckTestCase
+{
+    public RedundantModifierTest(String aName)
+    {
+        super(aName);
+    }
+
+    public void testIt()
+            throws Exception
+    {
+        final LocalizedMessages msgs = new LocalizedMessages(8);
+        final TreeWalker walker = new TreeWalker(msgs);
+        final CheckConfiguration config = new CheckConfiguration();
+        config.setClassname(RedundantModifierCheck.class.getName());
+        final Check c = config.createInstance(
+            Thread.currentThread().getContextClassLoader());
+        walker.registerCheck(c, config);
+        final String fname = CheckerTest.getPath("InputModifier.java");
+        final String[] lines = getLines(fname);
+        walker.walk(getAST(fname, lines), lines, fname);
+        assertEquals(2, msgs.getMessages().length);
+        int idx = 0;
+        verifyMessage(msgs, idx++, 32, 9, "Redundant 'public' modifier.");
+        verifyMessage(msgs, idx++, 38, 9, "Redundant 'abstract' modifier.");
+    }
+}