--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/gov/nasa/jpf/vm/Step.java	Fri Jan 23 10:14:01 2015 -0800
@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2014, United States Government, as represented by the
+ * Administrator of the National Aeronautics and Space Administration.
+ * All rights reserved.
+ *
+ * The Java Pathfinder core (jpf-core) platform is licensed under the
+ * Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ * 
+ *        http://www.apache.org/licenses/LICENSE-2.0. 
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and 
+ * limitations under the License.
+ */
+package gov.nasa.jpf.vm;
+
+import gov.nasa.jpf.util.Source;
+
+import java.util.WeakHashMap;
+
+/**
+ * this corresponds to an executed instruction. Note that we can have a
+ * potentially huge number of Steps, hence we want to save objects here
+ * (e.g. Collection overhead)
+ */
+public class Step {
+
+  private static WeakHashMap<Step, String> s_comments = new WeakHashMap<Step, String>();  // Not every Step gets a comment.  So save memory and put comments in a global comment HashMap.  Make this a WeakHashMap so that old Step objects can be GCed.
+
+  private final Instruction insn;
+  Step next;
+
+  public Step (Instruction insn) {
+    if (insn == null)
+      throw new IllegalArgumentException("insn == null");
+
+    this.insn = insn;
+  }
+
+  public Step getNext() {
+    return next;
+  }
+
+  public Instruction getInstruction() {
+    return insn;
+  }
+
+  public void setComment (String s) {
+    s_comments.put(this, s);
+  }
+
+  public String getComment () {
+    return s_comments.get(this);
+  }
+
+  public String getLineString () {
+    MethodInfo mi = insn.getMethodInfo();
+    if (mi != null) {
+      Source source = Source.getSource(mi.getSourceFileName());
+      if (source != null) {
+        int line = mi.getLineNumber(insn);
+        if (line > 0) {
+          return source.getLine(line);
+        }
+      }
+    }
+
+    return null;
+  }
+
+  public boolean sameSourceLocation (Step other){
+    
+    if (other != null){
+      MethodInfo mi = insn.getMethodInfo();
+      MethodInfo miOther = other.insn.getMethodInfo();
+      if (mi == miOther){
+        return (mi.getLineNumber(insn) == miOther.getLineNumber(other.insn));
+      }
+    }
+    
+    return false;
+  }
+  
+  public String getLocationString() {
+    MethodInfo mi = insn.getMethodInfo();
+    if (mi != null) {
+      return mi.getSourceFileName() + ':' + mi.getLineNumber(insn);
+    }
+
+    return "?:?";
+  }
+
+  @Override
+  public String toString() {
+    return getLocationString();
+  }
+}