diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrike/tools/ExtractMatchingClasses.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrike/tools/ExtractMatchingClasses.java
index 9182b2d66..7e9ab4f7a 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrike/tools/ExtractMatchingClasses.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrike/tools/ExtractMatchingClasses.java
@@ -42,6 +42,12 @@ public class ExtractMatchingClasses {
     }
     String in = args[0];
     String out = args[1];
+    if (in == null) {
+      throw new IllegalArgumentException("null args[0]");
+    }
+    if (out == null) {
+      throw new IllegalArgumentException("null args[1]");
+    }
     String[] match = new String[args.length - 2];
     System.arraycopy(args, 2, match, 0, match.length);
 
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/ConstantInstruction.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/ConstantInstruction.java
index 378dd811a..7fe4f26a9 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/ConstantInstruction.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/ConstantInstruction.java
@@ -457,8 +457,7 @@ public abstract class ConstantInstruction extends Instruction {
   }
 
   /**
-   * @return the constant value pushed: an Integer, a Long, a Float, a Double, a
-   *         String, or null
+   * @return the constant value pushed: an Integer, a Long, a Float, a Double, a String, or null
    */
   public abstract Object getValue();
 
@@ -478,17 +477,21 @@ public abstract class ConstantInstruction extends Instruction {
     } else if (type.equals(TYPE_Class)) {
       return makeClass((String) constant);
     } else {
-      switch (Util.getTypeIndex(type)) {
-      case TYPE_int_index:
-        return make(((Number) constant).intValue());
-      case TYPE_long_index:
-        return make(((Number) constant).longValue());
-      case TYPE_float_index:
-        return make(((Number) constant).floatValue());
-      case TYPE_double_index:
-        return make(((Number) constant).doubleValue());
-      default:
-        throw new IllegalArgumentException("Invalid type for constant: " + type);
+      try {
+        switch (Util.getTypeIndex(type)) {
+        case TYPE_int_index:
+          return make(((Number) constant).intValue());
+        case TYPE_long_index:
+          return make(((Number) constant).longValue());
+        case TYPE_float_index:
+          return make(((Number) constant).floatValue());
+        case TYPE_double_index:
+          return make(((Number) constant).doubleValue());
+        default:
+          throw new IllegalArgumentException("Invalid type for constant: " + type);
+        }
+      } catch (ClassCastException e) {
+        throw new IllegalArgumentException(e);
       }
     }
   }
@@ -540,7 +543,22 @@ public abstract class ConstantInstruction extends Instruction {
   final public boolean equals(Object o) {
     if (o instanceof ConstantInstruction) {
       ConstantInstruction i = (ConstantInstruction) o;
-      return i.getType().equals(getType()) && i.getValue().equals(getValue());
+      if (!i.getType().equals(getType())) {
+        return false;
+      }
+      if (i.getValue() == null) {
+        if (getValue() == null) {
+          return true;
+        } else {
+          return false;
+        }
+      } else {
+        if (getValue() == null) {
+          return false;
+        } else {
+          return i.getValue().equals(getValue());
+        }
+      }
     } else {
       return false;
     }
@@ -558,7 +576,8 @@ public abstract class ConstantInstruction extends Instruction {
 
   @Override
   final public int hashCode() {
-    return getType().hashCode() + 14411 * getValue().hashCode();
+    int v = getValue() == null ? 0 : getValue().hashCode();
+    return getType().hashCode() + 14411 * v;
   }
 
   @Override
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/InstanceofInstruction.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/InstanceofInstruction.java
index c2af623a0..33d92e02d 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/InstanceofInstruction.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/InstanceofInstruction.java
@@ -10,18 +10,19 @@
  *******************************************************************************/
 package com.ibm.wala.shrikeBT;
 
-import com.ibm.wala.annotations.NonNull;
 
 /**
  * This class represents instanceof instructions.
  */
 public final class InstanceofInstruction extends Instruction {
-  @NonNull
   final private String type;
 
   protected InstanceofInstruction(String type) {
     super(OP_instanceof);
     this.type = type;
+    if (type == null) {
+      throw new IllegalArgumentException("null type");
+    }
   }
 
   public static InstanceofInstruction make(String type) {
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/MethodEditor.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/MethodEditor.java
index b0c3c04f4..025a9d916 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/MethodEditor.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/MethodEditor.java
@@ -129,6 +129,9 @@ public final class MethodEditor {
    * instructions-to-bytecode-offsets map.
    */
   public MethodEditor(Instruction[] instructions, ExceptionHandler[][] handlers, int[] instructionsToBytecodes) {
+    if (instructions == null) {
+      throw new IllegalArgumentException("null instructions");
+    }
     methodInfo = null;
     this.instructionsToBytecodes = instructionsToBytecodes;
     this.instructions = instructions;
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/Util.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/Util.java
index 6a70d619a..97fad7b66 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/Util.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/Util.java
@@ -41,8 +41,8 @@ public final class Util {
    * @throws IllegalArgumentException  if s is null
    */
   public static byte getWordSize(String s) {
-    if (s == null) {
-      throw new IllegalArgumentException("s is null");
+    if (s == null || s.length() == 0) {
+      throw new IllegalArgumentException("invalid s: " + s);
     }
     return getWordSize(s, 0);
   }
@@ -210,8 +210,8 @@ public final class Util {
    * @throws IllegalArgumentException  if type == null
    */
   static int getParamsCount(String type) throws IllegalArgumentException {
-    if (type == null) {
-      throw new IllegalArgumentException("type == null");
+    if (type == null || type.length() < 2) {
+      throw new IllegalArgumentException("invalid type: " + type);
     }
     int index = 1;
     int count = 0;
@@ -289,8 +289,8 @@ public final class Util {
    * @throws IllegalArgumentException  if t is null
    */
   public static String getStackType(String t) {
-    if (t == null) {
-      throw new IllegalArgumentException("t is null");
+    if (t == null || t.length() < 1) {
+      throw new IllegalArgumentException("invalid t: " + t);
     }
     switch (t.charAt(0)) {
     case 'Z':
@@ -330,7 +330,7 @@ public final class Util {
    * @return true iff t is a primitive type
    */
   public static boolean isPrimitiveType(String t) {
-    if (t == null) {
+    if (t == null || t.length() == 0) {
       return false;
     } else {
       switch (t.charAt(0)) {
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Analyzer.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Analyzer.java
index 0eead4608..76f290411 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Analyzer.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Analyzer.java
@@ -55,6 +55,9 @@ public class Analyzer {
   protected final static int[] noEdges = new int[0];
 
   public Analyzer(boolean isStatic, String classType, String signature, IInstruction[] instructions, ExceptionHandler[][] handlers) {
+    if (instructions == null) {
+      throw new IllegalArgumentException("null instructions");
+    }
     this.classType = classType;
     this.isStatic = isStatic;
     this.signature = signature;
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Verifier.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Verifier.java
index c903f6c27..18e9e6d80 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Verifier.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/analysis/Verifier.java
@@ -56,26 +56,26 @@ import com.ibm.wala.shrikeBT.Util;
  *          System.out.println(&quot;Verification failed at instruction &quot;
  *              + ex.getOffset() + &quot;: &quot; + ex.getReason());
  *      }
- *  
+ * 
  * </pre>
  * 
- * For full verification you need to provide class hierarchy information using
- * setClassHierarchy. Without this information, we can't compute the exact types
- * of variables at control flow merge points. If you don't provide a hierarchy,
- * or the hierarchy you provide is partial, then the Verifier will be
- * optimistic.
+ * For full verification you need to provide class hierarchy information using setClassHierarchy. Without this information, we can't
+ * compute the exact types of variables at control flow merge points. If you don't provide a hierarchy, or the hierarchy you provide
+ * is partial, then the Verifier will be optimistic.
  * 
- * This method can also be used to gather type information for every stack and
- * local variable at every program point. Just call computeTypes() instead of
- * verify() and then retrieve the results with getLocalTypes() and
- * getStackTypes().
+ * This method can also be used to gather type information for every stack and local variable at every program point. Just call
+ * computeTypes() instead of verify() and then retrieve the results with getLocalTypes() and getStackTypes().
  */
 public final class Verifier extends Analyzer {
   final class VerifyVisitor extends TypeVisitor {
     private int curIndex;
+
     private List<PathElement> curPath;
+
     private FailureException ex;
+
     private String[] curStack;
+
     private String[] curLocals;
 
     VerifyVisitor() {
@@ -293,18 +293,17 @@ public final class Verifier extends Analyzer {
 
   /**
    * Initialize a verifier.
-   * @throws NullPointerException  if info is null
+   * 
+   * @throws NullPointerException if info is null
    */
   public Verifier(MethodData info) throws NullPointerException {
     super(info);
   }
 
   /**
-   * Try to verify the method. If verification is unsuccessful, we throw an
-   * exception.
+   * Try to verify the method. If verification is unsuccessful, we throw an exception.
    * 
-   * @throws FailureException
-   *           the method contains invalid bytecode
+   * @throws FailureException the method contains invalid bytecode
    */
   public void verify() throws FailureException {
     VerifyVisitor v = new VerifyVisitor();
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/shrikeCT/tools/AddSerialVersion.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/shrikeCT/tools/AddSerialVersion.java
index 269dcd037..cb9ea5cd3 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/shrikeCT/tools/AddSerialVersion.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/shrikeCT/tools/AddSerialVersion.java
@@ -182,6 +182,9 @@ public class AddSerialVersion {
 
   public static void main(String[] args) {
     for (int i = 0; i < args.length; i++) {
+      if (args[i] == null) {
+        throw new IllegalArgumentException("args[" + i + "] is null");
+      }
       try {
         byte[] data = Util.readFully(new FileInputStream(args[i]));
         ClassReader r = new ClassReader(data);
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/MethodOptimizer.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/MethodOptimizer.java
index 78584b5e0..b9498c92e 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/MethodOptimizer.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/MethodOptimizer.java
@@ -55,6 +55,9 @@ public final class MethodOptimizer {
   final static int[] noEdges = new int[0];
 
   public MethodOptimizer(MethodData d, MethodEditor e) {
+    if (d == null) {
+      throw new IllegalArgumentException("null d");
+    }
     this.data = d;
     this.editor = e;
   }
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/OfflineInstrumenterBase.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/OfflineInstrumenterBase.java
index d87b3a15b..793c9cada 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/OfflineInstrumenterBase.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeBT/tools/OfflineInstrumenterBase.java
@@ -322,6 +322,9 @@ public abstract class OfflineInstrumenterBase {
 
     for (int i = 0; i < args.length; i++) {
       String a = args[i];
+      if (a == null) {
+        throw new IllegalArgumentException("args[" + i + "] is null");
+      }
       if (a.equals("-o") && i + 1 < args.length) {
         setOutputJar(new File(args[i + 1]));
         i++;
@@ -600,7 +603,7 @@ public abstract class OfflineInstrumenterBase {
   /**
    * Call this when you're done modifying classes.
    */
-  final public void close() throws IOException {
+  final public void close() throws IOException, IllegalStateException {
     if (passUnmodifiedClasses) {
       writeUnmodifiedClasses();
     }
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ClassWriter.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ClassWriter.java
index d4fc25a50..806ef7770 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ClassWriter.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ClassWriter.java
@@ -902,13 +902,14 @@ public final class ClassWriter implements ClassConstants {
     if (buf == null) {
       throw new IllegalArgumentException("buf is null");
     }
-    if (offset >= buf.length) {
+    try {
+      buf[offset] = (byte) (v >> 24);
+      buf[offset + 1] = (byte) (v >> 16);
+      buf[offset + 2] = (byte) (v >> 8);
+      buf[offset + 3] = (byte) v;
+    } catch (ArrayIndexOutOfBoundsException e) {
       throw new IllegalArgumentException("illegal offset " + offset);
     }
-    buf[offset] = (byte) (v >> 24);
-    buf[offset + 1] = (byte) (v >> 16);
-    buf[offset + 2] = (byte) (v >> 8);
-    buf[offset + 3] = (byte) v;
   }
 
   /**
@@ -942,10 +943,14 @@ public final class ClassWriter implements ClassConstants {
     if (buf == null) {
       throw new IllegalArgumentException("buf is null");
     }
-    if (offset + 1 >= buf.length) {
+    if (offset < 0 || offset + 1 >= buf.length) {
       throw new IllegalArgumentException("buf is too short " + buf.length + " " + offset);
     }
-    buf[offset] = (byte) (v >> 8);
-    buf[offset + 1] = (byte) v;
+    try {
+      buf[offset] = (byte) (v >> 8);
+      buf[offset + 1] = (byte) v;
+    } catch (ArrayIndexOutOfBoundsException e) {
+      throw new IllegalArgumentException("invalid offset: " + offset);
+    }
   }
 }
\ No newline at end of file
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ConstantPoolParser.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ConstantPoolParser.java
index e1483a5b1..c62c71d1c 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ConstantPoolParser.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/ConstantPoolParser.java
@@ -19,6 +19,9 @@ public final class ConstantPoolParser implements ClassConstants {
   private int[] cpOffsets;
 
   private String[] cpItems;
+  
+  // TODO: use JVM spec limit here?
+  private final static int MAX_CP_ITEMS = Integer.MAX_VALUE / 4;
 
   /**
    * @param bytes the raw class file data
@@ -30,7 +33,7 @@ public final class ConstantPoolParser implements ClassConstants {
     if (offset < 0) {
       throw new IllegalArgumentException("invalid offset: " + offset);
     }
-    if (itemCount < 0) {
+    if (itemCount < 0 || itemCount > MAX_CP_ITEMS) {
       throw new IllegalArgumentException("invalid itemCount: " + itemCount);
     }
     parseConstantPool(offset, itemCount);
diff --git a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/LocalVariableTableWriter.java b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/LocalVariableTableWriter.java
index 2d8726394..2ad52db5f 100644
--- a/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/LocalVariableTableWriter.java
+++ b/com.ibm.wala.shrike/src/com/ibm/wala/shrikeCT/LocalVariableTableWriter.java
@@ -17,13 +17,15 @@ import java.util.Arrays;
  */
 public final class LocalVariableTableWriter extends ClassWriter.Element {
   final private int attrID;
+
   private int[] rawTable = emptyTable;
 
   private static final int[] emptyTable = new int[0];
 
   /**
    * Create a blank LocalVariableTable.
-   * @throws IllegalArgumentException  if w is null
+   * 
+   * @throws IllegalArgumentException if w is null
    */
   public LocalVariableTableWriter(ClassWriter w) {
     if (w == null) {
@@ -33,12 +35,9 @@ public final class LocalVariableTableWriter extends ClassWriter.Element {
   }
 
   /**
-   * Set the raw local variable table values. Consider using
-   * LocalVariableTableWriter.makeRawTable to build the raw values.
+   * Set the raw local variable table values. Consider using LocalVariableTableWriter.makeRawTable to build the raw values.
    * 
-   * @param table
-   *          the raw values, a flattened sequence of (startPC, length,
-   *          nameIndex, typeIndex, var) tuples
+   * @param table the raw values, a flattened sequence of (startPC, length, nameIndex, typeIndex, var) tuples
    */
   public void setRawTable(int[] table) {
     if (table == null) {
@@ -83,73 +82,74 @@ public final class LocalVariableTableWriter extends ClassWriter.Element {
   /**
    * Build a raw local variable table from a formatted variable map.
    * 
-   * @param varMap
-   *          an array mapping bytecode offsets to a variable map for each
-   *          offset; a variable map is a array of 2*localVars elements,
-   *          containing a (nameIndex, typeIndex) for each local variable; the
-   *          pair (0,0) indicates that there is no information about that local
-   *          variable at that offset
-   * @throws IllegalArgumentException  if varMap == null
+   * @param varMap an array mapping bytecode offsets to a variable map for each offset; a variable map is a array of 2*localVars
+   *          elements, containing a (nameIndex, typeIndex) for each local variable; the pair (0,0) indicates that there is no
+   *          information about that local variable at that offset
+   * @throws IllegalArgumentException if varMap == null
    */
   public static int[] makeRawTable(int[][] varMap) throws IllegalArgumentException {
     if (varMap == null) {
       throw new IllegalArgumentException("varMap == null");
     }
-    int varCount = 0;
-    for (int i = 0; i < varMap.length; i++) {
-      if (varMap[i] != null) {
-        varCount = Math.max(varCount, varMap[i].length);
+    try {
+      int varCount = 0;
+      for (int i = 0; i < varMap.length; i++) {
+        if (varMap[i] != null) {
+          varCount = Math.max(varCount, varMap[i].length);
+        }
       }
-    }
-    varCount /= 2;
+      varCount /= 2;
 
-    int[] entries = new int[20];
-    int[] varEnd = new int[varCount];
-    Arrays.fill(varEnd, -1);
-    int[] lastVector = null;
-    int entryCount = 0;
-    for (int i = 0; i < varMap.length; i++) {
-      if (varMap[i] != lastVector) {
-        lastVector = varMap[i];
+      int[] entries = new int[20];
+      int[] varEnd = new int[varCount];
+      Arrays.fill(varEnd, -1);
+      int[] lastVector = null;
+      int entryCount = 0;
+      for (int i = 0; i < varMap.length; i++) {
+        if (varMap[i] != lastVector) {
+          lastVector = varMap[i];
 
-        if (lastVector != null) {
-          for (int k = 0; k < lastVector.length / 2; k++) {
-            if (lastVector[k * 2] > 0 && i >= varEnd[k]) {
-              int entryOffset = entryCount * 5;
-              entryCount++;
-              if (entryCount * 5 > entries.length) {
-                int[] newEntries = new int[entries.length * 2];
-                System.arraycopy(entries, 0, newEntries, 0, entries.length);
-                entries = newEntries;
-              }
-              int nameIndex = lastVector[k * 2];
-              int typeIndex = lastVector[k * 2 + 1];
-              int end = i + 1;
-              while (end < varMap.length) {
-                if (varMap[end] == null || k * 2 >= varMap[end].length || varMap[end][k * 2] != nameIndex
-                    || varMap[end][k * 2 + 1] != typeIndex) {
-                  break;
+          if (lastVector != null) {
+            for (int k = 0; k < lastVector.length / 2; k++) {
+              if (lastVector[k * 2] > 0 && i >= varEnd[k]) {
+                int entryOffset = entryCount * 5;
+                entryCount++;
+                if (entryCount * 5 > entries.length) {
+                  int[] newEntries = new int[entries.length * 2];
+                  System.arraycopy(entries, 0, newEntries, 0, entries.length);
+                  entries = newEntries;
                 }
-                end++;
+                int nameIndex = lastVector[k * 2];
+                int typeIndex = lastVector[k * 2 + 1];
+                int end = i + 1;
+                while (end < varMap.length) {
+                  if (varMap[end] == null || k * 2 >= varMap[end].length || varMap[end][k * 2] != nameIndex
+                      || varMap[end][k * 2 + 1] != typeIndex) {
+                    break;
+                  }
+                  end++;
+                }
+                varEnd[k] = end;
+                entries[entryOffset] = i;
+                entries[entryOffset + 1] = end - i;
+                entries[entryOffset + 2] = nameIndex;
+                entries[entryOffset + 3] = typeIndex;
+                entries[entryOffset + 4] = k;
               }
-              varEnd[k] = end;
-              entries[entryOffset] = i;
-              entries[entryOffset + 1] = end - i;
-              entries[entryOffset + 2] = nameIndex;
-              entries[entryOffset + 3] = typeIndex;
-              entries[entryOffset + 4] = k;
             }
           }
         }
       }
-    }
 
-    if (entryCount == 0) {
-      return null;
-    } else {
-      int[] r = new int[entryCount * 5];
-      System.arraycopy(entries, 0, r, 0, r.length);
-      return r;
+      if (entryCount == 0) {
+        return null;
+      } else {
+        int[] r = new int[entryCount * 5];
+        System.arraycopy(entries, 0, r, 0, r.length);
+        return r;
+      }
+    } catch (ArrayIndexOutOfBoundsException e) {
+      throw new IllegalArgumentException("malformed varMap");
     }
   }
 }
\ No newline at end of file