Slides used for tutorial at EclipseCon 2012 http://www.eclipsecon.org/2012/sessions/how-train-jdt-dragon

1. How To Train the JDT Dragon
Ayushman Jain Stephan Herrmann
IBM Bangalore, India GK Software AG, Berlin
ayushman.jain@in.ibm.com stephan@cs.tu-berlin.de

2. Acknowledgements
Title credits: Deepak Azad (JDT/UI
Committer, IBM Bangalore).
Thanks to the entire JDT team for all the hard
work!

3. The JDT Team
Olivier Thomann
Daniel Megert
Markus Keller
Deepak Azad Ayushman Jain
Satyam Rama Kandula Jayaprakash Arthanareeswaran
Srikanth Adayapalam
Stephan Herrmann
3

4. Outline
• A guided tour through services offered by JDT Core and JDT
UI
• Java Model
TM
• Search Engine and Type Hierarchy
• Abstract Syntax Tree (DOM/AST)
• Batch compiler
• A sneak preview of Object Teams and how it helps in
extending JDT
• Three hands-on exercises
4

5. Installing software for the tutorial
• 1. Install "Eclipse SDK" M6 from the Juno download site:
You can install either 3.8M6(http://download.eclipse.org/eclipse/downloads/eclipse3x.php ) or 4.2M6 (
http://download.eclipse.org/eclipse/downloads/ ) depending on what you prefer.
• 2. Install JDT's "ASTView Plugin" using the update site (
http://www.eclipse.org/jdt/ui/update-site ) . Add this site in Help -> Install New Software... and select the ASTView
plugin.
• 3. Install Egit: http://download.eclipse.org/egit/updates
Note: If you're new to git, we will provide you some basic steps to follow that will be needed during the tutorial.
However, if you're still not comfortable, feel free to skip this part.
From the above update site, install "Eclipse Egit".
• 4. Create another copy of your Juno M6 installation folder and install Object Teams in it:
Go to Help -> Install New Software... and add the Object teams update site
(http://download.eclipse.org/objectteams/updates/ot2.1milestones). Select everything under the category OTDT 2.1
based on Eclipse 3.8" and install.
• 5. Refer to https://github.com/aupsy/org.eclipsecon2012.misc.tutorial/blob/master/Handouts/git-handout_v3.pdf
for instructions on how to obtain the sources and handouts.

6. What do you learn?
• Plug-in implementers that want to use the Java infrastructure
• Programmatically create/work with Java resources, (viz.
generating/modifying source code).
• Programmatically launch java applications.
• Refactoring / quick fixes / content assist.
• Implementers of plug-ins for a new language
• Study JDT as an example on how to structure the core
infrastructure.
• Solve problems regarding memory usage and runtime
performance.
General knowledge about the Eclipse plug-in architecture and
basic knowledge of Java is expected.
6

7. Components of JDT
• JDT/Core – headless infrastructure for compiling
and modifying java code.
• JDT UI - the user interface extensions that
provide the IDE.
• JDT Debug - program launching and debug
support specific to the Java programming
language.
• JDT APT – JDT’s annotation processing
framework.
• JDT Text – editing support.

8. Anatomy of the JDT Dragon
AST: Abstract Syntax Tree
Java Model
Fine-grained, fully resolved compiler Search Engine
Lightweight model for views parse tree
Indexes of declarations,
• OK to keep references to it • No references to it must be kept:
references and type
• Contains unresolved Clients have to make sure only a
hierarchy relationships
information limited number of ASTs is loaded at
• From projects to declarations the same time
(types, methods,...) • Fully resolved information
• From a Java file (‘Compilation Unit’) to
identifier tokens

9. The Wings: Java Model
Java Model – classes that model java resources
• Java project and its elements
• Classpath elements
• Java project settings
• Creating a Java element
• Change notification
• Type hierarchy
• Code Assist & Code resolve
AST – Precise, fully resolved compiler parse tree
9 Search Engine

10. The Java Model - Design Motivation
• Requirements for an element to show in views:
• Lightweight: Quickly created, small memory footprint
• Must scale and work for big workspaces (10’000 types
and more). Cannot hold on resources, Eclipse is not just a
Java IDE
• Fault tolerant: Provide structure for files while editing
• Some source does not (yet) compile, missing brackets,
semicolons. Tooling should be as helpful as possible
• Views like the Outline want to show the structure while
typing. Structure should stay as stable as possible
• Chosen solution:
• Lazily populated model
• Quick creation: Single parse, no resolving, no dependency on
build state
10
• Underlying buffer can be released and recreated any time

11. IJavaElements form a hierarchy that represents the
entire workspace from Java angle Java Elements
• Different from resource hierarchy
Important to note: API
• Not all Java elements must have an underlying resource
(elements inside a JAR, external JAR files)
• A Java package doesn’t have the same children as a IJavaProject
folder (no concept of subfolder)
IPackageFragmentRoot
JavaCore.create(resource)
IPackageFragment
IType
ICompilationUnit /
IMethod IClassFile
IField element.getParent()
IProject IInitialzier
IFolder
element.getChildren()
IFile
javaElement.getResource()
11

12. Java Element Handles
Handle/Info design
• IJavaElement objects are lightweight: OK to keep
references
• Underlying buffer (‘element info’) created on demand
• Element doesn’t need to exist or be on the build path
(anymore). Use IJavaElement#exists() to test
• Handle representation stable between workspace
sessions
String handleId= javaElement.getHandleIdentifier();
IJavaElement elem= JavaCore.create(handleId);
12

13. Using the Java Model
Setting up a Java project
• A Java project is a project with the Java nature set
• Java nature enables the Java builder
• Java builder needs a Java class path
IWorkspaceRoot root= ResourcesPlugin.getWorkspace().getRoot();
IProject project= root.getProject(projectName);
Create a project
project.create(null);
project.open(null);
IProjectDescription description = project.getDescription(); Set the
description.setNatureIds(new String[] { JavaCore.NATURE_ID }); Java nature
project.setDescription(description, null);
IJavaProject javaProject= JavaCore.create(project);
javaProject.setRawClasspath(classPath, defaultOutputLocation, null);
Set the Java
build path
13

14. Java Classpath
The Java element hierarchy is defined by the Java classpath:
Classpath entries define the roots of package fragments.
14

15. Classpath – Source and Library Entries
Source entry: Java source files to be built by the compiler
• Folder inside the project or the project itself
• Possibility to define inclusion and exclusion filters
• Compiled files go to either a specific or the projects default output
location
IPath srcPath= javaProject.getPath().append("src");
IPath[] excluded= new IPath[] { new Path("doc") };
IClasspathEntry srcEntry= JavaCore.newSourceEntry(srcPath, excluded);
NEW
Library entries can now specify
Library entry: Class folder or archive index locations for faster search
Class files in folder or JAR archive, in workspace or external
Source attachment specifies location of library’s source
IClasspathEntry libEntry = JavaCore.newLibraryEntry( new Path("d:/lib/foo.jar"), // library
location new Path("d:/lib/foo_src.zip"), // source archive location
new Path("src"), // source archive root
true); // exported
15
Java project can also be added as a newProjectEntry

16. Java Classpath: Container Entries
• Container entry: Multiple entries through an indirection
• Path denotes name and arguments for a ‘classpath container’
entry= JavaCore.newContainerEntry(new Path("containerId/containerArguments"));
• Classpath containers are contributed by extension point
• Classpath containers can compute classpath entries when first used
• Built-in containers: JRE, User library, JUnit, PDE dependencies
jreCPEntry= JavaCore.newContainerEntry(new Path(JavaRuntime.JRE_CONTAINER));
• Extension point ‘org.eclipse.jdt.core.classpathContainerInitializer’
• Initializes and manages containers (using
JavaCore.setClasspathContainer(..))
• Extension point ‘org.eclipse.jdt.ui.classpathContainerPage’
• Contributes a classpath container configuration page
16

17. Creating Java Elements
IJavaProject javaProject= JavaCore.create(project); Set the build path
IClasspathEntry[] buildPath= {
JavaCore.newSourceEntry(project.getFullPath().append("src")),
JavaRuntime.getDefaultJREContainerEntry()
};
javaProject.setRawClasspath(buildPath, project.getFullPath().append("bin"), null);
IFolder folder= project.getFolder("src"); Create the source folder
folder.create(true, true, null);
IPackageFragmentRoot srcFolder= javaProject.getPackageFragmentRoot(folder);
Assert.assertTrue(srcFolder.exists()); // resource exists and is on build path
Create the package fragment
IPackageFragment fragment= srcFolder.createPackageFragment("x.y", true, null);
String str= Create the compilation unit,
"package x.y;" + "n" +
"public class E {" + "n" +
including a type
" String first;" + "n" +
"}";
ICompilationUnit cu= fragment.createCompilationUnit("E.java", str, false, null);
IType type= cu.getType("E"); Create a field
type.createField("String name;", null, true, null);
17

18. Java Project Settings
Configure compiler settings on the project
• Compiler compliance, class file compatibility, source
compatibility
(JavaCore.COMPILER_COMPLIANCE, JavaCore.COMPILER_CODEGEN_TARGET_PLATFORM,
JavaCore.COMPILER_SOURCE )
• Compiler problems severities (Ignore/Warning/Error)
javaProject.setOption(JavaCore.COMPILER_COMPLIANCE, JavaCore.VERSION_1_5);
NEW javaProject.setOption(JavaCore.COMPILER_ANNOTATION_NULL_ANALYSIS,
JavaCore.ENABLED);
If not set on the project, taken from the workspace settings
• Project settings persisted in project/.settings/org.eclipse.jdt.core.prefs
• Used to share the settings in the team
• More project specific settings: Formatter, code templates,…
See Platform preferences story
18 • Platform.getPreferencesService()

19. Working Copies
• A compilation unit in a buffered state is a working copy
• Primary working copy: shared buffer shown by all editors
• based on the Eclipse Platform’s buffer manager (plug-in org.eclipse.core.filebuffers)
• becomeWorkingCopy(...): Increment count, internally create buffer, if first
• commitWorkingCopy(): Apply buffer to underlying resource
• discardWorkingCopy(): Decrement count, discard buffer, if last
• Element stays the same, only state change
• Private working copy: Build a virtual Java model layered on top of the current
content
• ICompilationUnit.getWorkingCopy(workingCopyOwner) returns a new element with a
new buffer (managed by the workingCopyOwner) based on the underlying element
• commitWorkingCopy(): Apply changes to the underlying element
• Refactoring uses this to first try all changes in a sandbox to only apply them if
compilable
• Working copy owner: Connects working copies so that they reference each
other
19

20. Java Element Change Notifications
Change Listeners: JavaCore.addElementChangedListener(IElementChangedListener)
Java element delta information for all changes: Class path changes, added/removed
elements, changed source, change to buffered state (working copy)
Changes triggered by resource change notifications (resource deltas), call to
‘reconcile()’
Java element deltas do not contain the old state (not a diff)
The granularity ends at the member level (no AST)
Table: IJavaElementDelta - Description of changes of an element or its children
Delta kind Descriptions and additional flags
ADDED Element has been added
REMOVED Element has been removed
CHANGED F_CONTENT Content has changed. If F_FINE_GRAINED is set: Analysis of
structural changed has been performed
F_MODIFIERS Changed modifiers
F_CHILDREN Deltas in children IJavaElementDelta[] getAffectedChildren()
F_ADDED_TO_CLASSPATH, F_SOURCEATTACHED, F_REORDER,
F_PRIMARY_WORKING_COPY,…
20

21. JavaElementListener – an Example
Find out if types were added or removed
fJavaListener= new IElementChangedListener() {
public void elementChanged(ElementChangedEvent event) {
boolean res= hasTypeAddedOrRemoved(event.getDelta());
}
Parent constructs:
private boolean hasTypeAddedOrRemoved(IJavaElementDelta delta) {
IJavaElement elem= delta.getElement();
Recursively go
boolean isAddedOrRemoved= (delta.getKind() != IJavaElementDelta.CHANGED); down the delta tree
switch (elem.getElementType()) {
case IJavaElement.JAVA_MODEL: case IJavaElement.JAVA_PROJECT:
case IJavaElement.PACKAGE_FRAGMENT_ROOT: case IJavaElement.PACKAGE_FRAGMENT:
if (isAddedOrRemoved) return true;
return processChildrenDelta(delta.getAffectedChildren());
case IJavaElement.COMPILATION_UNIT:
ICompilationUnit cu= (ICompilationUnit) elem; Be aware of
if (!cu.getPrimary().equals(cu)) private
return false; working copies
if (isAddedOrRemoved || isPossibleStructuralChange(delta.getFlags()))
return true;
return processChildrenDelta(delta.getAffectedChildren());
case IJavaElement.TYPE:
if (isAddedOrRemoved) return true;
return processChildrenDelta(delta.getAffectedChildren()); // inner types
default: // fields, methods, imports...
return false;
21 }
}
}

22. JavaElementListener – cont’d
private static boolean isPossibleStructuralChange(int flags) {
return hasSet(flags, IJavaElementDelta.F_CONTENT)
&& !hasSet(flags , IJavaElementDelta.F_FINE_GRAINED));
}
private boolean processChildrenDelta(IJavaElementDelta[] children) {
for (int i= 0; i < children.length; i++) {
if (hasTypeAddedOrRemoved(children[i])) ‘Fine Grained’ set means that
return true; children deltas have been
}
return false;
computed. If not, it is a unknown
} change (potentially full change)
Visit delta children recursively
22

23. Code Assist
See Also:
jdt.ui.JavaTypeCompletionProposalComputer
ICodeAssist.codeCo
mplete(..)
accept(..)
acceptContext(..)
extends
javaCompletionProposalComputer

24. Type Hierarchy - Design Motivation
Subtype hierarchies are expensive to create and maintain.
Why not having an API IType.getSubtypes()?
• Bad performance for repeated queries in the same hierarchy
Why not keep a constantly updated hierarchy in memory?
• Does not scale for big workspaces. JDT is not alone in the workbench and
should avoid holding on to lots of memory.
• Expensive updating. Every class path change would require types to
recheck if they still resolve to the same type
Chosen solution:
• Explicit hierarchy object
• Defined life cycle
• Well known creation costs (sub type relationship is stored in index files)
• Allows scoped hierarchies
24

25. Type Hierarchy
• Snapshot of ITypes in a sub/super type relationship
• Used in Type Hierarchy view
25

26. Type Hierarchy
• Create – on a type or on a region (= set of Java Elements)
typeHierarchy= type.newTypeHierarchy(progressMonitor);
typeHierarchy= project.newTypeHierarchy(region, progressMonitor);
• Supertype hierarchy – faster!
typeHierarchy= type.newSupertypeHierarchy(progressMonitor);
• Get super and subtypes, interfaces and classes
typeHierarchy.getSubtypes(type)
• Change listener – when changed, refresh is required
typeHierarchy.addTypeHierarchyChangedListener(..);
typeHierarchy.refresh(progressMonitor);
26

27. Code Resolve
• Resolve the element at the given offset and length in the source
javaElements= compilationUnit.codeSelect(50, 10);
• Used for Navigate > Open (F3) and tool tips
27

28. Code Resolve – an Example
Set up a
compilation unit
Resolving the reference to “String” in a compilation unit
String content =
"public class X {" + "n" +
" String field;" + "n" +
"}";
ICompilationUnit cu=
fragment.createCompilationUnit(“X.java", content, false, null);
int start = content.indexOf("String");
int length = "String".length();
IJavaElement[] declarations = cu.codeSelect(start, length);
Contains a single IType:
‘java.lang.String’
28

29. More Java Model Features
Navigation – resolve a name
IType type= javaProject.findType("java.util.Vector");
Context – resolve an enclosing element
element= compilationUnit.getElementAt(position);
Code assist – evaluate completions for a given offset
compilationUnit.codeComplete(offset, resultRequestor);
Code formatting
ToolFactory.createCodeFormatter(options)
.format(kind, string, offset, length, indentationLevel, lineSeparator);
29

30. API in JDT UI
Labels, images, structure, order for IJavaElements:
• JavaElementLabelProvider
• StandardJavaElementContentProvider
• JavaElementComparator
Selection and configuration dialogs, wizards
• JavaUI.createPackageDialog(..), JavaUI.createTypeDialog(..)
• BuildPathDialogAccess
• NewClassWizardPage, NewInterfaceWizardPage…
• JavadocExportWizardPage, NewJavaProjectWizardPageOne /
Two
Java Actions to add to context menus
• package org.eclipse.jdt.ui.actions
• org.eclipse.jdt.ui.actions.OpenAttachedJavadocAction
30

31. The Backbone: AST
Java Model – Lightweight model for views
Search Engine
AST – Precise, fully resolved compiler parse tree
• Overall design
• Creating an AST
• AST node details
• Bindings
• AST rewrite
• Refactoring toolkit
31

32. Abstract Syntax Tree - Design
Motivation
• Java Model and type hierarchy
• optimized to present model elements in a view.
• Refactorings and code manipulation features
• need fully resolved information down to statement level
to perform exact code analysis.
• Need a way to manipulate source code on a higher abstraction than
characters.
• Chosen solution:
• On-demand created abstract syntax tree with all resolved bindings
• Defined life cycle
• Well known creation costs
• Abstract syntax tree rewriter to manipulate code on language element level
32

33. Abstract Syntax Tree
The human eye sees:
ASTParser#createAST(...)
JDT Dragon sees:
AST
ReturnStatement
expression
InfixExpression
leftOperand rightOperand
resolveBinding
IMethodBinding MethodInvocation SimpleName
33

34. Abstract Syntax Tree cond’t
A Java type for each syntactic construct
Assignment, CastExpression, ConditionalExpression…
Bindings for type information
Can resolve all references through bindings
Visitors and node properties for analysis
ASTRewriter to manipulate an AST
34

35. AST Workflow
additional symbol resolved information
called bindings may be present.
Two ways:
• direct manipulation or
• through a ‘scratchpad’ i.e. ASTRewrite

36. Creating an AST
• Build AST with AST factory: ASTParser
• Either from Java model elements: ICompilationUnit, IClassFile
(ITypeRoot)
• Or source string, file name and IJavaProject as context
• Bindings or no bindings
• Bindings contain resolved information. Fully available on syntax-error-
free code, best effort when there are errors.
• Full AST or partial AST
• For a given source position: All other methods have empty bodies
• AST for an element: Only method, statement or expression
36

37. Creating an AST
• Statements recovery
• No recovery: When detecting syntax error: Skip method body
• With recovery: Skip tokens, or introduce artificial tokens to create
statements.
Recovered node are flagged with ASTNode#RECOVERED
• Bindings recovery
• No recovery: No bindings if element can not be found
(for example is not on the class path)
• With recovery: Introduce recovered bindings, only name is correct,
no package or members. Bindings marked with binding.isRecovered()
• Create multiple ASTs using same binding environment, much faster
• setIgnoreMethodBodies(boolean): Can be used when the method bodies
are not needed. This saves a lot of memory.
• Bindings can be resolved without an Eclipse workspace:
37 ASTParser#setEnvironment(..)

38. Creating an AST
Create AST on an element
ASTParser parser= ASTParser.newParser(AST.JLS3);
parser.setSource(cu);
parser.setResolveBindings(true);
parser.setStatementsRecovery(true);
ASTNode node= parser.createAST(null);
Create AST on source string
ASTParser parser= ASTParser.newParser(AST.JLS3);
parser.setSource("System.out.println();".toCharArray());
parser.setProject(javaProject);
parser.setKind(ASTParser.K_STATEMENTS);
parser.setStatementsRecovery(false);
ASTNode node= parser.createAST(null);
38

39. AST Browsing
Typed access to the node children:
ConditionalExpression:
getExpression()
getThenExpression()
getElseExpression()
Homogenous access using node
properties:
List allProperties= node.structuralPropertiesForType();
Will contain 3 elements of type ‘StructuralPropertyDescriptor’:
ConditionalExpression.EXPRESSION_PROPERTY,
ConditionalExpression.THEN_EXPRESSION_PROPERTY,
ConditionalExpression.ELSE_EXPRESSION_PROPERTY ,
expression=
node.getStructuralProperty(ConditionalExpression.EXPRESSION_PROPERTY);
39

40. AST View
private void print(ASTNode node) {
List properties= node.structuralPropertiesForType();
for (Iterator iterator= properties.iterator(); iterator.hasNext();) {
Object descriptor= iterator.next();
if (descriptor instanceof SimplePropertyDescriptor) {
SimplePropertyDescriptor simple= (SimplePropertyDescriptor)descriptor;
Object value= node.getStructuralProperty(simple);
System.out.println(simple.getId() + " (" + value.toString() + ")");
} else if (descriptor instanceof ChildPropertyDescriptor) {
ChildPropertyDescriptor child= (ChildPropertyDescriptor)descriptor;
ASTNode childNode= (ASTNode)node.getStructuralProperty(child);
if (childNode != null) {
System.out.println("Child (" + child.getId() + ") {");
print(childNode);
System.out.println("}");
}
} else {
ChildListPropertyDescriptor list= (ChildListPropertyDescriptor)descriptor;
System.out.println("List (" + list.getId() + "){");
print((List)node.getStructuralProperty(list));
System.out.println("}");
}
}
}
private void print(List nodes) {
for (Iterator iterator= nodes.iterator(); iterator.hasNext();) {
print( (ASTNode) iterator.next() );
}
40
}

41. ASTView Demo
ASTView and JavaElement view:
http://www.eclipse.org/jdt/ui/update-site
41

42. Bindings
Bindings are fully connected
• ITypeBinding has bindings for super type, interfaces, all members
• IMethodBinding has bindings for parameter types, exceptions,
return type
• IVariableBinding has binding for variable type
Bindings retain a lot of memory:
• Do not hold on bindings
• Do not hold on ASTNodes that contain bindings
Within an AST:
• Binding identity (can use ‘==‘ to compare bindings)
Bindings from different ASTs:
• isEqualTo(…)
42 • Or compare binding.getKey()

43. Bindings cont’d
From a binding to an IJavaElement:
• binding.getJavaElement()
From a binding to its declaring ASTNode:
• All within the same context:
astRoot.findDeclaringNode(binding) (on CompilationUnit)
• If binding is from a different AST:
astRoot.findDeclaringNode(foreignBinding.getKey())
• Looking for a node in a different CU:
cu = binding.getJavaElement().getCompilationUnit();
astParser.setSource(cu);
otherRoot = astParser.createAst(…);
otherRoot.findDeclaringNode(binding.getKey());
43

44. More Utility Classes
• E.g.: NodeFinder:
• From a position to an ASTNode
• For more please see
http://wiki.eclipse.org/JDT/FAQ
• Please help us maintaining this list

45. AST Visitor
ASTParser parser= ASTParser.newParser(AST.JLS3);
parser.setSource(cu);
parser.setResolveBindings(true);
ASTNode root= parser.createAST(null); Count the number of casts
root.accept(new ASTVisitor() {
public boolean visit(CastExpression node) {
fCastCount++;
return true; Count the number of references to
} a field of ‘java.lang.System’
(‘System.out’, ‘System.err’)
public boolean visit(SimpleName node) {
IBinding binding= node.resolveBinding();
if (binding instanceof IVariableBinding) {
IVariableBinding varBinding= (IVariableBinding) binding;
ITypeBinding declaringType= varBinding.getDeclaringClass();
if (varBinding.isField() &&
"java.lang.System".equals(declaringType.getQualifiedName())) {
fAccessesToSystemFields++;
}
}
return true;
}
45

46. AST Rewriting
• Instead of manipulating the source code, change the AST and
write changes back to source
• Descriptive approach
• describe changes without actually modifying the AST
• allows reuse of the AST for multiple independent rewrites
• support generation of a preview
• Modifying approach
• start by: ast.recordModifications();
• directly manipulates the AST
• API is more intuitive
• implemented using the descriptive rewriter: ast.rewrite()
• Rewriter characteristics
• preserves user formatting and markers
46 • generates a TextEdit that describes document changes

47. AST Rewriting cont’d
Implementation of descriptive rewrite is more powerful:
• String placeholders: Use a node that is a placeholder for
an arbitrary string of code or comments
• Track node positions: Get the new source ranges after the
rewrite
• Copy/move a range of nodes
• Modify the comment mapping heuristic used by the rewriter
(comments are associated with nodes. Operation on nodes
also include the associated comments)
47

48. Copy/Move details
void foo(Foo f) {
if (f != null) { 1. t=r.createMoveTarget(node);
f.bar1();
}
2. l.insert(t);
bar2(); t 3. l2.removeLast();
}
If original should be kept:
void foo(Foo f) {
if (f != null) { • use createCopyTarget(node);
f.bar1();
bar2();
}
}

49. AST Rewrite cont’d
Example of the descriptive AST rewrite:
public void modify(MethodDeclaration decl) {
Create the rewriter
AST ast= decl.getAST();
Change the method name
ASTRewrite astRewrite= ASTRewrite.create(ast);
SimpleName newName= ast.newSimpleName("newName");
astRewrite.set(decl, MethodDeclaration.NAME_PROPERTY, newName, null);
ListRewrite paramRewrite=
astRewrite.getListRewrite(decl, MethodDeclaration.PARAMETERS_PROPERTY);
SingleVariableDeclaration newParam= ast.newSingleVariableDeclaration();
newParam.setType(ast.newPrimitiveType(PrimitiveType.INT));
newParam.setName(ast.newSimpleName("p1"));
paramRewrite.insertFirst(newParam, null);
TextEdit edit= astRewrite.rewriteAST(document, null); Insert a new parameter as
first parameter
edit.apply(document); Create resulting edit script
49 } Apply edit script to source buffer
See also: ImportRewrite

50. Code Manipulation Toolkits
• Refactoring – org.eclipse.ltk.refactoring
• refactorings - org.eclipse.ltk.core.refactoring.Refactoring
• responsible for precondition checking
• create code changes
• code changes - org.eclipse.ltk.core.refactoring.Change
• provide Undo/Redo support
• support non-textual changes (e.g. renaming a file)
• support textual changes based on text edit support
• user interface is wizard-based
• Quick Fix & Quick Assist – org.eclipse.jdt.ui.text.java
• processors - org.eclipse.jdt.ui.text.java.IQuickFixProcessor
• check availability based on problem identifier
• generate a list of fixes
• user interface is provided by editor
50

51. The Eyes: Search Engine
Java Model – Lightweight model for views
AST – Precise, fully resolved compiler parse tree
Search Engine
• Design motivation
• Using the search engine
• Code example
51

52. Search Engine – Design Motivation
• Need quick access to all references or declarations of a Java element
• Searching for all references to type “A”
• Used to build call graphs
• All types in workspace
• Trade-off between search and update performance
• Chosen solution:
• Index based search engine
• Index is “word” based. It doesn’t contain resolved information (e.g.
class U references method foo(), not method A#foo()).
• Special resolve step needed to narrow down matches reported
from index (e.g. searching for B#foo() must not report U).
52

53. Search Engine
• Search for declarations and references
• packages, types, fields, methods and constructors
• using wildcards (including camel-case) or from a Java element
• Scoped search
• region = set of Java elements
• predefined workspace and hierarchy scopes
• Potential matches
• Code with errors, incomplete class paths
• Limit the match locations
• in casts, in catch clauses, only return types…
53

54. Search Engine – Using the APIs
• Creating a search pattern
SearchPattern.createPattern("foo*",
IJavaSearchConstants.FIELD, IJavaSearchConstants.REFERENCES,
SearchPattern.R_PATTERN_MATCH | SearchPattern.R_CASE_SENSITIVE);
• Creating a search scope
SearchEngine.createWorkspaceScope();
SearchEngine.createJavaSearchScope(new IJavaElement[] { project });
SearchEngine.createHierarchyScope(type);
SearchEngine.createStrictHierarchyScope(
project,
type,
onlySubtypes,
includeFocusType,
progressMonitor);
• Collecting results
• Subclass SearchRequestor
• Each result reported as a SearchMatch
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55. Search Engine – an Example
Searching for all declarations of methods “foo” that return an int Search pattern
SearchPattern pattern = SearchPattern.createPattern(
"foo(*) int",
IJavaSearchConstants.METHOD,
IJavaSearchConstants.DECLARATIONS,
SearchPattern.R_PATTERN_MATCH);
Search scope
IJavaSearchScope scope = SearchEngine.createWorkspaceScope();
SearchRequestor requestor = new SearchRequestor() {
public void acceptSearchMatch(SearchMatch match) {
System.out.println(match.getElement());
Result
}
collector
};
SearchEngine searchEngine = new SearchEngine(); Start search
searchEngine.search(
pattern,
new SearchParticipant[] { SearchEngine.getDefaultSearchParticipant()},
scope,
requestor,
null /*progress monitor*/);
55

56. The Batch Compiler
• Eclipse provides and uses its own compiler that is not javac
• The Eclipse compiler is used inside the IDE (Eclipse)
• The Eclipse compiler can also be used as a pure batch compiler outside of Eclipse
• The Eclipse batch compiler can be used as:
• A command line tool
• A compiler adapter inside an Ant task:
• As a compiler service used by the Compiler API (jsr 199)
56

57. Extending the JDT
• Can be fun, if
• API exposes what you need to see
• Extension points exist where you want to adapt
• JDT offers a wealth of API and extension points
• Not every RFE can create new API
• Conflicts with other clients
• Performance impact
• Maintenance costs
• What if your RFE gets rejected?
• Abandon your project?
• Copy&Paste
• Use Object Teams

58. The JDT Dragon meets Object Teams
Ayushman Jain Stephan Herrmann
IBM Bangalore, India GK Software AG, Berlin
ayushman.jain@in.ibm.com stephan@cs.tu-berlin.de

59. Relation between two Projects
Debug UI
commi lead
... t
JDT
Core OTDT
Object Teams
Equinox OT/Equinox
Java OT/J
59

60. Cheat with Style
• What if API is missing?
• Ignore restrictions, even private
• What if extension point is missing?
• We have other means for extending:
• specialize instances not classes
• What about maintainability?
• Do minimal harm
• Group extensions to higher-level modules: teams.

61. Exercise Stopwatch
• New → Example → Stop Watch Example
• src / ... / Main.java
→ Run As → Java Application
Note: to stop application click (Console view)
Find role class WatchUI.WatchDisplay:
• When are instances of this role created ?
• When is its method update() called?
Extra (Demo):
• Terminate application when watch is reset at 3 seconds.

62. OT/Equinox
Plug-in B
Plug-in C
export
Team1 CC1 «aspectBinding» CB2
R1 CB1
rmbm «playedBy»
internal
R2 CB4
«playedBy» CB3

63. Exercise: AntiDemo Plug-in
• Write a new Plug-in
• adapting org.eclipse.jdt.core
• Change the Java naming rules
• Class names cannot start with “Foo”
• Hint: JavaConventions#validateXZY()
• In a runtime workbench
• Try to create a class “Foobar”
• Be inventive!
Note: you may need to scroll to see
Enable OT/Equinox

64. Demo: Reachability Analysis
• Implement a Plug-in that finds unreachable code.
• All “main” methods are considered reachable.
• All methods called from a reachable method are also reachable.
• Method calls inside dead code should not be considered.
(e.g. “if (false) m();”)
• Analyzing method calls must consider polymorphism /overriding.
• Methods that are only called from unreachable methods are not
reachable (including “islands”: cycles of unreachable methods).
Need a whole-system call graph.
+ local flow analysis
+ inheritance information

65. Design
• Piggy-back on the JDT compiler
• Find all MethodDeclarations during resolve
• Record start nodes, like “main” methods
• Create a graph of MethodBindings
• Connect nodes when analysing MessageSends
• Ignore calls in dead code
• Start from set of all methods
• subtract all methods reachable from a start node
• consider method overriding
• Only work during full build
• report remaining methods after subtracting

66. No Limits – No Pain
playedBy: every object is extensible
callout: every method / field can be made accessible
callin: every method is overridable
warnings for decapsulation: proceed at your own (low) risk
• interface (bidirectional) fully explicit
• lean & mean = powerful & maintainable

67. Extending the JDT into new Dimensions
• Each feature is a module / team
• Define suitable structure using teams & roles
• Create connections using playedBy, callout & callin

68. Summary
• JDT delivers powerful program manipulation services
• Java Model, Search engine and DOM AST
• Use them to add your own tool to the Eclipse Java IDE
• but also in headless mode (can be used programmatically)
• E.g. EMF, metrics tools, …
• Full J2SE 5.0/6.0/7.0 support
• Full-fledged batch compiler
• Community feedback is essential
• bug reports:
https://bugs.eclipse.org/bugs/enter_bug.cgi?product=JDT
• Forum:
http://www.eclipse.org/forums/index.php/f/13
68

69. Give Feedback on the Sessions
1 Sign In: www.eclipsecon.org
2 Select Session Evaluate
3 Vote

70. Legal Notice
• Copyright © IBM Corp., 2007-2012. All rights reserved. This presentation and
the source code in it are made available under the EPL, v1.0.
• Java and all Java-based trademarks are trademarks of Sun Microsystems, Inc.
in the United States, other countries, or both.
• Eclipse and the Eclipse logo are trademarks of Eclipse Foundation, Inc.
• IBM and the IBM logo are trademarks or registered trademarks of IBM
Corporation, in the United States, other countries or both.
• Other company, product, or service names may be trademarks or service
marks of others.
• THE INFORMATION DISCUSSED IN THIS PRESENTATION IS PROVIDED
FOR INFORMATIONAL PURPOSES ONLY. WHILE EFFORTS WERE MADE
TO VERIFY THE COMPLETENESS AND ACCURACY OF THE
INFORMATION, IT IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY
KIND, EXPRESS OR IMPLIED, AND IBM SHALL NOT BE RESPONSIBLE
FOR ANY DAMAGES ARISING OUT OF THE USE OF, OR OTHERWISE
RELATED TO, SUCH INFORMATION. ANY INFORMATION CONCERNING
IBM'S PRODUCT PLANS OR STRATEGY IS SUBJECT TO CHANGE BY IBM
WITHOUT NOTICE
70