Recommending Automated Extract Method Refactorings (ICPC 2014)

Extract Method is a key refactoring for improving program comprehension. However, recent empirical research shows that refactoring tools designed to automate Extract Methods are often underused. To tackle this issue, we propose a novel approach to identify and rank Extract Method refactoring opportunities that are directly automated by IDE-based refactoring tools. Our approach aims to recommend new methods that hide structural dependencies that are rarely used by the remaining statements in the original method. We conducted an exploratory study to experiment and define the best strategies to compute the dependencies and the similarity measures used by the proposed approach. We also evaluated our approach in a sample of 81 extract method opportunities generated for JUnit and JHotDraw, achieving a precision of 48% (JUnit) and 38% (JHotDraw).

Transcript

1. Danilo Silva
   Dept. of Computer Science
   UFMG, Brazil
   danilofs@dcc.ufmg.br
   Recommending Automated Extract
   Method Refactorings
   Ricardo Terra
   Dept. of Computer Science
   UFLA, Brazil
   terra@dcc.ufla.br
   Marco Tulio Valente
   Dept. of Computer Science
   UFMG, Brazil
   mtov@dcc.ufmg.br
   APPLIED SOFTWARE ENGINEERING
   RESEARCH GROUP
   /
   

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2. Introduction
   Extract Method Refactoring
    Used in a wide range of scenarios
    IDE-based automated support available, but underused
   2
   

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3. Proposed Solution
    Automated identification of Extract Method opportunities
   3
   01 public String execute() throws Exception {
   02 logger.info("Starting execute()");
   03 Session sess = HibernateUtil.getSessionFactory().openSession();
   04 Transaction t = sess.beginTransaction();
   05 Criteria criteria = sess.createCriteria(User.class);
   06 criteria.add(Restrictions.idEq(this.user.getUsername()));
   07 criteria.add(Restrictions.eq("password", this.user.getPassword()));
   08 User user = (User) criteria.uniqueResult();
   09 t.commit();
   10 sess.close();
   11 if (user != null) {
   12 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
   13 logger.info("Finishing execute() -- Success");
   14 return SUCCESS;
   15 }
   16 this.addActionError(this.getText("login.failure"));
   17 logger.info("Finishing execute() -- Failure");
   18 return INPUT;
   19 }
   

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4. Proposed Solution
   JExtract
    Generation of Extract Method candidates
    Scoring function
    Structural similarity between dependency sets
    Filtering
   4
   

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5. Generation of Candidates
    Analysis of the AST to split the code into blocks
    For each block
    For each subsequence of statements
    Check if it is a candidate for extraction
   5
   

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6. Generation of Candidates
    Moving window algorithm
   6
   01 public String execute() throws Exception {
   02 1/01 logger.info("Starting execute()");
   03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
   04 1/03 Transaction t = sess.beginTransaction();
   05 1/04 Criteria criteria = sess.createCriteria(User.class);
   06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
   07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
   08 1/07 User user = (User) criteria.uniqueResult();
   09 1/08 t.commit();
   10 1/09 sess.close();
   11
   1/10
   if (user != null) {
   12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
   13 2/02 logger.info("Finishing execute() -- Success");
   14 2/03 return SUCCESS;
   15 }
   16 1/11 this.addActionError(this.getText("login.failure"));
   17 1/12 logger.info("Finishing execute() -- Failure");
   18 1/13 return INPUT;
   19 }
   

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7. Generation of Candidates
    Moving window algorithm
   6
   01 public String execute() throws Exception {
   02 1/01 logger.info("Starting execute()");
   03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
   04 1/03 Transaction t = sess.beginTransaction();
   05 1/04 Criteria criteria = sess.createCriteria(User.class);
   06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
   07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
   08 1/07 User user = (User) criteria.uniqueResult();
   09 1/08 t.commit();
   10 1/09 sess.close();
   11
   1/10
   if (user != null) {
   12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
   13 2/02 logger.info("Finishing execute() -- Success");
   14 2/03 return SUCCESS;
   15 }
   16 1/11 this.addActionError(this.getText("login.failure"));
   17 1/12 logger.info("Finishing execute() -- Failure");
   18 1/13 return INPUT;
   19 }
   

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8. Generation of Candidates
    Moving window algorithm
   6
   01 public String execute() throws Exception {
   02 1/01 logger.info("Starting execute()");
   03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
   04 1/03 Transaction t = sess.beginTransaction();
   05 1/04 Criteria criteria = sess.createCriteria(User.class);
   06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
   07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
   08 1/07 User user = (User) criteria.uniqueResult();
   09 1/08 t.commit();
   10 1/09 sess.close();
   11
   1/10
   if (user != null) {
   12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
   13 2/02 logger.info("Finishing execute() -- Success");
   14 2/03 return SUCCESS;
   15 }
   16 1/11 this.addActionError(this.getText("login.failure"));
   17 1/12 logger.info("Finishing execute() -- Failure");
   18 1/13 return INPUT;
   19 }
   

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9. Generation of Candidates
    Moving window algorithm
   6
   01 public String execute() throws Exception {
   02 1/01 logger.info("Starting execute()");
   03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
   04 1/03 Transaction t = sess.beginTransaction();
   05 1/04 Criteria criteria = sess.createCriteria(User.class);
   06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
   07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
   08 1/07 User user = (User) criteria.uniqueResult();
   09 1/08 t.commit();
   10 1/09 sess.close();
   11
   1/10
   if (user != null) {
   12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
   13 2/02 logger.info("Finishing execute() -- Success");
   14 2/03 return SUCCESS;
   15 }
   16 1/11 this.addActionError(this.getText("login.failure"));
   17 1/12 logger.info("Finishing execute() -- Failure");
   18 1/13 return INPUT;
   19 }
   

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10. Generation of Candidates
     Moving window algorithm
    6
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    

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11. Generation of Candidates
     Moving window algorithm
    6
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    

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12. Generation of Candidates
     Moving window algorithm
    6
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    

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13. Generation of Candidates
     Moving window algorithm
    6
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    

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14. Generation of Candidates
     Moving window algorithm
    6
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    

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15. Generation of Candidates
     Moving window algorithm
    6
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    

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16. Scoring Function
     Structural dependencies
     Three levels:
     Variables
     Types
     Packages
    7
    

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17. Scoring Function
     Variables
    8
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    Dependency on variable criteria
    

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18. Scoring Function
     Types
    9
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    Method of type Criteria invoked
    Dependency on type Criteria
    

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19. Scoring Function
     Packages
    10
    01 public String execute() throws Exception {
    02 1/01 logger.info("Starting execute()");
    03 1/02 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 1/03 Transaction t = sess.beginTransaction();
    05 1/04 Criteria criteria = sess.createCriteria(User.class);
    06 1/05 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 1/06 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 1/07 User user = (User) criteria.uniqueResult();
    09 1/08 t.commit();
    10 1/09 sess.close();
    11
    1/10
    if (user != null) {
    12 2/01 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 2/02 logger.info("Finishing execute() -- Success");
    14 2/03 return SUCCESS;
    15 }
    16 1/11 this.addActionError(this.getText("login.failure"));
    17 1/12 logger.info("Finishing execute() -- Failure");
    18 1/13 return INPUT;
    19 }
    Dependency on package org.hibernate
    (where Criteria belongs to)
    

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20. Scoring Function
     Two dependency sets:
     The code fragment to be extracted Dep
     The remaining statements Dep’
     Dep should not be similar to Dep’
     Extracted fragment should hide complexity
    11
    Dep’
    (Remaining)
    Dep
    (Extracted)
    Good Bad
    Dep’
    (Remaining)
    Dep
    (Extracted)
    

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21. Scoring Function
    12
     Distance using Kulczynski set similarity coefficient
     Final scoring function
    

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22. Case study: MyWebMarket
     Small Web application
     25 well-known Extract Method instances
     14 of then supported by IDEs
    13
    Approach #Recom. #Found Recall Prec.
    JExtract (top-1) 14 12 85.7% 85.7%
    JExtract (top-2) 28 14 100.0% 50.0%
    JExtract (top-3) 42 14 100.0% 33.3%
    JDeodorant 20 2 14.3% 10.0%
    

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23. Case study: JUnit and JHotDraw
     Well-known opportunities introduced by inlining methods
     25 in JUnit
     56 in JHotDraw
    14
    System Approach #Reco. #Found Recall Prec.
    JUnit
    (25 known
    opport.)
    JExtract (top-1) 25 12 48.0% 48.0%
    JExtract (top-2) 29 16 64.0% 32.7%
    JExtract (top-3) 72 18 72.0% 25.0%
    JDeodorant 39 0 0.0% 0.0%
    JHotDraw
    (56 known
    opport.)
    JExtract (top-1) 56 21 37.5% 37.5%
    JExtract (top-2) 110 28 50.0% 25.5%
    JExtract (top-3) 162 33 58.9% 20.4%
    JDeodorant 67 4 7.1% 6.0%
    

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24. Future Work
     New evaluation with developers
     Statement reordering before extracting the code fragment
     Combine Extract Method with Move Method
    15
    

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25. Thank you
    16
    APPLIED SOFTWARE ENGINEERING
    RESEARCH GROUP
    /
    

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26. Extra slide
     Some of JDeodorant’s recommendations incorrectly
    reordered statements involving database transactions
    17
    01 public String execute() throws Exception {
    02 logger.info("Starting execute()");
    03 Session sess = HibernateUtil.getSessionFactory().openSession();
    04 Transaction t = sess.beginTransaction();
    05 Criteria criteria = sess.createCriteria(User.class);
    06 criteria.add(Restrictions.idEq(this.user.getUsername()));
    07 criteria.add(Restrictions.eq("password", this.user.getPassword()));
    08 User user = (User) criteria.uniqueResult();
    09 t.commit();
    10 sess.close();
    11 if (user != null) {
    12 ActionContext.getContext().getSession().put(AUTHENTICATED_USER, user);
    13 logger.info("Finishing execute() -- Success");
    14 return SUCCESS;
    15 }
    16 this.addActionError(this.getText("login.failure"));
    17 logger.info("Finishing execute() -- Failure");
    18 return INPUT;
    19 }
    

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