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Table
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of
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Contents
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| Table of Contents |
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Vision
- Create a platform to enable language designers and the community to validate extensions to Java.
- Encourage and facilitate empirical research of features in Java.
A Query Language for Language Designers
Java Source Code Query Languages
In this section, we give an overview of the seven query languages that we evaluate in this paper: Java Tools Language, Browse-By-Query,
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SOUL,
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JQuery,
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.QL,
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Jackpot
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and
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PMD.
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We
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selected
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these
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languages
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because
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they
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provide
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a
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variety
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of
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design
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choices
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and
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strictly
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provide
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a
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query
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language.
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For
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example,
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we
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didn't
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select
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Findbugs
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as
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it
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only
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lets
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programmers
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query
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source
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by
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creating
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new
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classes
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based
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on
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a
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Java
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framework.
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We
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also
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only
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selected
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source
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code
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query
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languages
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that
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included
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a
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guide
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or
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a
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working
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implementation.
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Java
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Language
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Tools
The Java Tools Language (JTL)
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is
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a
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logic-paradigm
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query
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language
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to
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select
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Java
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elements
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in
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a
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code
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base.
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The
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current
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implementation
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is
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based
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on
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an
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analysis
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of
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Java
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bytecode
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classes.
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The
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JTL
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syntax
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is
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inspired
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by
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Query-by-Example
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ideas
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in
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order
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to
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increase
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productivity
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of
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users.
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For
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example,
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one
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could
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find
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all
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methods
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taking
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three
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int
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parameters
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and
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returning
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a
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subclass
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of
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Java's
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Date
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class
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using
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the
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follow
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query:
| Code Block |
|---|
} public static D method(int, int, int), D extends* /java.util.Date; {code} |
In
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addition,
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JTL
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features
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variable
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binding
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and
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data
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flow
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queries.
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Browse-By-Query
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Browse-By-Query
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(BBQ)
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reads
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Java
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bytecode
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files
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and
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creates
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a
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database
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representing
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classes,
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method
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calls,
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fields,
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field
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references,
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string
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constants
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and
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string
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constant
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references.
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This
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database
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can
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then
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be
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interrogated
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through
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English-like
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queries.
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The
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syntax
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is
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motivated
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by
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the
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desire
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to
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be
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intuitive.
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For
...
example,
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one
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could
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find
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all
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the
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methods
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that
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call
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a
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method
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whose
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name
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matches
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start
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by
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composing
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the
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following
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query:
| Code Block |
|---|
} methods containing calls to matching "start" methods in all classes {code} |
In
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addition,
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BBQ
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provides
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filtering
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mechanisms,
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set
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and
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and
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relational
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operators
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that
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can
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be
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combined
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to
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compose
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more
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complex
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queries.
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SOUL
SOUL is a logic-paradigm
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query
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language.
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It
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contains
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an
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extensive
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predicate
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library
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called
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CAVA
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that
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matches
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queries
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against
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AST
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nodes
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of
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a
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Java
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program
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generated
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by
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the
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Eclipse
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JDT.
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SOUL
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facilitates
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the
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specification
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of
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queries
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by
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using
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example-driven
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matching
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of
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templates
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and
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structural
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unification
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to
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match
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a
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code
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excerpt
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with
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an
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AST
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node.
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In
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practice,
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this
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means
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a
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user
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can
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create
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a
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logic
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variable
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to
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match
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an
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AST
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node
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and
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reuse
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this
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variable
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within
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the
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query
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regardless
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of
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the
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execution
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path
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where
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the
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variable
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appears.
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For
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example,
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one
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could
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specify
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a
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query
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that
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finds
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instances
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of
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Scanner
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that
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is
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read
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after
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it
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was
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closed
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as
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follows:
| Code Block |
|---|
{code} if jtMethodDeclaration(?m){ public static void main(String[] args) { ?scanner := [new java.util.Scanner(?argList);] ?scanner.close(); ?scanner.next(); } } {code} h4. JQuery h5. JQuery is a |
JQuery
JQuery is a logic-paradigm
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query
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language
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built
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on
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top
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of
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the
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logic
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programming
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language
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TyRuBa.
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The
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implementation
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of
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JQuery
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analyse
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the
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AST
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of
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a
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Java
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program
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by
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making
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calls
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to
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the
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Eclipse
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JDT.
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JQuery
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includes
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a
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library
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of
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predicates
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that
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allows
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querying
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Java
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elements
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and
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the
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relationships
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between
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them.
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For
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example,
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the
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following
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query
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finds
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all
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method
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declarations
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?M
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that
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have
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at
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least
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one
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parameter
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of
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type
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Integer:
| Code Block |
|---|
} method(?M, paramType, ?PT), match(?PT, /Integer/). {code} h4. |
.QL
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.QL is an object-oriented
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query
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language.
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It
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enables
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programmers
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to
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query
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Java
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source
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code
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by
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composing
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queries
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that
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look
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like
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SQL.
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The
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motivation
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for
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this
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design
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choice
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is
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to
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reduce
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barrier
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to
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entry
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for
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developers
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that
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learn
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it.
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In
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addition,
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the
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authors
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argue
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that
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object-orientation
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provides
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the
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structure
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necessary
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for
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building
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reusable
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queries.
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An
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implementation
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is
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available,
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called
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SemmleCode,
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which
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includes
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an
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editor
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and
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various
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optimisations.
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As
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an
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example,
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the
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following
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query
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describes
...
how
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to
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find
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all
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classes
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that
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declare
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a
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method
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equals,
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but
...
which
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do
...
not
...
specify
...
a
...
method
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hashCode.
| Code Block |
|---|
} from Class c where c.declaresMethod("equals") and not (c.declaresMethod("hashCode")) and c.fromSource() select c.getPackage(), c {code} h4. Jackpot h5. Jackpot is a module for the NetBeans IDE for querying and transforming Java source files. Jackpot lets user query the AST of a Java program by composing rules under the form of a Java expression. In addition, one can specify variables to bind to a matching AST node. For example, the following query will match any code surrounded by a call to readLock() and readUnlock(): |
Jackpot
Jackpot is a module for the NetBeans IDE for querying and transforming Java source files. Jackpot lets user query the AST of a Java program by composing rules under the form of a Java expression. In addition, one can specify variables to bind to a matching AST node. For example, the following query will match any code surrounded by a call to readLock() and readUnlock():
| Code Block |
|---|
{code} $document.readLock(); $statementsUnderLock$; $document.readUnlock(); {code} |
PMD
PMD is a ruleset based Java source code analyzer that identifies bugs or potential problems including dead code, duplicate code or overcomplicated expressions. PMD has an extensive archive of built-in rules that can be used to identify such problems. One can specify new rules by writing it in Java and making use of the PMD helper classes. Alternatively, one can also compose custom rules via an XPath expression that queries the AST of the program to analyze. For example, the following query finds all method declarations that have at least one parameter of type Integer:
| Code Block |
|---|
h4. PMD h5. PMD is a ruleset based Java source code analyzer that identifies bugs or potential problems including dead code, duplicate code or overcomplicated expressions. PMD has an extensive archive of built-in rules that can be used to identify such problems. One can specify new rules by writing it in Java and making use of the PMD helper classes. Alternatively, one can also compose custom rules via an XPath expression that queries the AST of the program to analyze. For example, the following query finds all method declarations that have at least one parameter of type Integer: {code} //MethodDeclarator/FormalParameters [FormalParameter/Type/ReferenceType/ClassOrInterfaceType [@Image = 'Integer']] {code} |
Uses Cases
In this section, we describe the use cases examined for the evaluation. We selected use cases that are source of language design discussions and make use of a variety of Java features.
Final Array and Anonymous Inner Classes
Java lets programmers create inner classes, which is a nested class not declared static. There exists three different types of inner classes: non-static member, local and anonymous classes.
Inner classes have a restriction that any local variable, formal parameter, or exception parameter used but not declared in the inner class must be declared final.
However, programmers can circumvent this restriction by declaring a final array with only one element and mutate the element of the array. The following code illustrates this mechanism:
| Code Block |
|---|
public class OutsideClass { h3. Uses Cases In this section, we describe the use cases examined for the evaluation. We selected use cases that are source of language design discussions and make use of a variety of Java features. h4. Final Array and Anonymous Inner Classes Java lets programmers create inner classes, which is a nested class not declared static. There exists three different types of inner classes: non-static member, local and anonymous classes. Inner classes have a restriction that any local variable, formal parameter, or exception parameter used but not declared in the inner class must be declared final. However, programmers can circumvent this restriction by declaring a final array with only one element and mutate the element of the array. The following code illustrates this mechanism:\\ {code} public class OutsideClass { public void methodA() { final String\[\] s = new String\[1\]; class InnerClass { { public void methodB() { s\[0\ { s[0] = "bypass"; // accepted by compiler } } } } {code}\\ *Use Case 1*: Find occurrence of an anonymous inner class whose code references a final array variable in the enclosing scope and which mutates array elements via that variable. h5. h4. Generic Constructors h5. h5. A constructor can have two sets of type arguments. A constructor can use the type parameters declared in a generic class. One can then specify the types after the class name: \texttt{new Foo<Integer>()}. In addition, a constructor can declare its own type parameters. The types are then specified between the \texttt{new} token and the class name: \texttt{new <Integer> Foo<Number>()}. The code below illustrates a constructor of class \texttt{Foo} which declares its own type parameter \texttt{S} that } } } } |
Use Case 1: Find occurrence of an anonymous inner class whose code references a final array variable in the enclosing scope and which mutates array elements via that variable.
Generic Constructors
A constructor can have two sets of type arguments. A constructor can use the type parameters declared in a generic class. One can then specify the types after the class name: new Foo<Integer>(). In addition, a constructor can declare its own type parameters. The types are then specified between the new token and the class name: new <Integer> Foo<Number>(). The code below illustrates a constructor of class Foo which declares its own type parameter S that extends the class's own parameters.
| Code Block |
|---|
extends the class's own parameters.{code}class Foo<T extends Number> { <S extends T> Foo() {}}{code} h5. A constructor can have two sets of type arguments. A constructor can use the type parameters declared in a generic class. One can then specify the types after the class name: new Foo<Integer>(). In addition, a constructor can declare its own type parameters. The types are then specified between the new token and the class name: new <Integer> Foo<Number>(). The code below illustrates a constructor of class Foo which declares its own type parameter S that extends the class's own parameters. h5. {code}class Foo<T extends Number> { h5. <S extends T> Foo() {} h5. }{code} h5. Capture Conversion Idiom h5. Overloaded Methods h5. Covariant Arrays h3. Evaluation || || Final Array & Anonymous Class || Generic Constructors || Capture Conversion Idiom || Overloaded Methods || Covariant Arrays || | +JTL+ | | | X | | | | +BBQ+ | X | X | X | * ?* | | | +SOUL+ | | | | | | | +JQuery+ | X | X | X | *?* | X | | +.QL+ | | | | | | | +Jackpot+ | | | | | | | +PMD+ | | | | | | *{+}JTL{+}* * *{+}BBQ{+}* * {color:#ff0000}doesn't detect local inner classes (local & anonymous). Only inner classes (doesn't differentiate): class in all classes{color} * {color:#ff0000}no access to local variable declared in methods{color} * {color:#ff0000}no support for generics on declaration.{color} * {color:#ff0000}no support for constructors (considered as method init) {color} * {color:#ff0000}no AST structural matching. (e.g loops ...){color} * {color:#ff0000}no variable binding/unification{color} * {color:#008000}set operators (union, intersection){color} * {color:#008000}support for read/write of{color} {color:#008000}{+}fields{+}{color} {color:#008000}references{color} *{+}SOUL{+}* * *{+}Jquery{+}* * [ } |
Capture Conversion Idiom
Overloaded Methods
Covariant Arrays
Evaluation
| Final Array & Anonymous Class | Generic Constructors | Capture Conversion Idiom | Overloaded Methods | Covariant Arrays |
|---|---|---|---|---|---|
JTL |
|
| X |
|
|
BBQ | X | X | X | ? |
|
SOUL |
|
|
|
|
|
JQuery | X | X | X | ? | X |
.QL |
|
|
|
|
|
Jackpot |
|
|
|
|
|
PMD |
|
|
|
|
|
JTL
BBQ
- doesn't detect local inner classes (local & anonymous). Only inner classes (doesn't differentiate): class in all classes
- no access to local variable declared in methods
- no support for generics on declaration.
- no support for constructors (considered as method init)
- no AST structural matching. (e.g loops ...)
- no variable binding/unification
- set operators (union, intersection)
- support for read/write of fields references
SOUL
Jquery
...
...
- variable binding through predicates
Wiki Markup support for read & mutation of fields (write) \[writes(?B,?F,?L) means: "Block ?B writes to field ?F at location ?L"\]
...
- no structural matching (e.g
...
- pattern
...
- match
...
- on
...
- a
...
- loop
...
- or
...
- body
...
- of
...
- a
...
- method)
...
- no generics support
.QL
Jackpot
...
PMD
Time Plan
| Week 1 | Week 2 | Week 3 | Week 4 | Week 5 |
July | Raoul in Cambridge |
|
|
|
|
August |
|
|
|
|
|
September |
|
|
|
|
|
October | Joel JavaOne |
| Raoul in Cambridge | Raoul in Cambridge | Raoul in Cambridge |
Color scheme:
- Alex
- Joel
- Raoul
Relevant Literature
| Wiki Markup |
|---|
\[1\] Brian Goetz. Language designer's notebook: Quantitative language design. [http://www.ibm.com/developerworks/java/library/j-ldn1/|http://www.ibm.com/developerworks/java/library/j-ldn1/]. |
...
| Wiki Markup |
|---|
\[2\] Chris Parnin, Christian Bird, and Emerson Murphy-Hill. 2011. Java generics adoption: how new features are introduced, championed, or ignored. In Proceedings of the 8th Working Conference on Mining Software Repositories (MSR '11) |
...
| Wiki Markup |
|---|
\[3\] Ewan Tempero, Craig Anslow, Jens Dietrich, Ted Han, Jing Li, Markus Lumpe, Hayden Melton, and James Noble. 2010. The Qualitas Corpus: A Curated Collection of Java Code for Empirical Studies. In Proceedings of the 2010 Asia Pacific Software Engineering Conference (APSEC '10) |
...
| Wiki Markup |
|---|
\[4\] Joseph Gil and Keren Lenz. 2010. The use of overloading in JAVA programs. In Proceedings of the 24th European conference on Object-oriented programming (ECOOP '10) |
...
| Wiki Markup |
|---|
\[5\] Raoul-Gabriel Urma and Janina Voigt. Using the OpenJDK to Investigate Covariance in Java. Java Magazine May/June 2012. |
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Related
...
Projects
| Wiki Markup |
|---|
\[a\] Refactoring NG. [http://kenai.com/projects/refactoringng|http://kenai.com/projects/refactoringng] |
...
| Wiki Markup |
|---|
\[b\] Tal Cohen, Joseph (Yossi) Gil, and Itay Maman. 2006. JTL: the Java tools language. In Proceedings of the 21st annual ACM SIGPLAN conference on Object-oriented programming systems, languages, and applications (OOPSLA '06) |
...
| Wiki Markup |
|---|
\[c\] Browse By Query. [http://browsebyquery.sourceforge.net/|http://browsebyquery.sourceforge.net/] |
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