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A Java Optimization Framework
There is a newer version: 4.6.0
package soot.jimple.toolkits.callgraph;

/*-
 * #%L
 * Soot - a J*va Optimization Framework
 * %%
 * Copyright (C) 2003 Ondrej Lhotak
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import soot.MethodOrMethodContext;
import soot.util.queue.ChunkedQueue;
import soot.util.queue.QueueReader;

/**
 * Keeps track of the methods transitively reachable from the specified entry points through the given call graph edges.
 *
 * @author Ondrej Lhotak
 */
public class ReachableMethods {
  protected CallGraph cg;
  protected Iterator edgeSource;
  protected final ChunkedQueue reachables = new ChunkedQueue<>();
  protected final Set set = new HashSet<>();
  protected QueueReader unprocessedMethods;
  protected final QueueReader allReachables = reachables.reader();
  protected Filter filter;

  public ReachableMethods(CallGraph graph, Iterator entryPoints) {
    this(graph, entryPoints, null);
  }

  public ReachableMethods(CallGraph graph, Iterator entryPoints, Filter filter) {
    this.filter = filter;
    this.cg = graph;
    addMethods(entryPoints);
    unprocessedMethods = reachables.reader();
    this.edgeSource = graph.listener();
    if (filter != null) {
      this.edgeSource = filter.wrap(this.edgeSource);
    }
  }

  public ReachableMethods(CallGraph graph, Collection entryPoints) {
    this(graph, entryPoints.iterator());
  }

  protected void addMethods(Iterator methods) {
    while (methods.hasNext()) {
      addMethod(methods.next());
    }
  }

  protected void addMethod(MethodOrMethodContext m) {
    if (set.add(m)) {
      reachables.add(m);
    }
  }

  /**
   * Causes the QueueReader objects to be filled up with any methods that have become reachable since the last call.
   */
  public void update() {
    while (edgeSource.hasNext()) {
      Edge e = edgeSource.next();
      if (e != null) {
        MethodOrMethodContext srcMethod = e.getSrc();
        if (!e.isInvalid() && srcMethod != null && set.contains(srcMethod)) {
          addMethod(e.getTgt());
        }
      }
    }
    while (unprocessedMethods.hasNext()) {
      MethodOrMethodContext m = unprocessedMethods.next();
      Iterator targets = cg.edgesOutOf(m);
      if (filter != null) {
        targets = filter.wrap(targets);
      }
      addMethods(new Targets(targets));
    }
  }

  /**
   * Returns a QueueReader object containing all methods found reachable so far, and which will be informed of any new
   * methods that are later found to be reachable.
   */
  public QueueReader listener() {
    return allReachables.clone();
  }

  /**
   * Returns a QueueReader object which will contain ONLY NEW methods which will be found to be reachable, but not those that
   * have already been found to be reachable.
   */
  public QueueReader newListener() {
    return reachables.reader();
  }

  /** Returns true iff method is reachable. */
  public boolean contains(MethodOrMethodContext m) {
    return set.contains(m);
  }

  /** Returns the number of methods that are reachable. */
  public int size() {
    return set.size();
  }
}