Add Comments by using Eclipse JDT ASTRewrite

Category: Java Development Tools (JDT) June 10, 2012

This code example belongs to the Eclipse JDT tutorial series.

The goal of this code example is add a comment to the following code.

public class Main {
	public static void main(String[] args) {
		int i = 1;
		System.out.println(i);
	}
	public static void add() {
		int i = 1;
		System.out.println(i);
	}
}

After adding a comment before the first statement of the first method, it becomes the following:

public class Main {
	public static void main(String[] args) {
		//mycomment
		int i = 1;
		System.out.println(i);
	}
	public static void add() {
		int i = 1;
		System.out.println(i);
	}
}

In order to add a comment to java source code, we need to use ASTRewrite. The tutorial from eclipse programmer's guide does not work. The main reason is missing of the following statement:

unit.getBuffer().setContents(document.get());

Here is the working code tested under Eclipse Indigo.

private void AddComments() throws MalformedTreeException, BadLocationException, CoreException {
 
	IProject project = ResourcesPlugin.getWorkspace().getRoot().getProject("testAddComments");
	IJavaProject javaProject = JavaCore.create(project);
	IPackageFragment package1 = javaProject.getPackageFragments()[0];
 
	//get first compilation unit
	ICompilationUnit unit = package1.getCompilationUnits()[0];
 
	// parse compilation unit
	CompilationUnit astRoot = parse(unit);
 
	//create a ASTRewrite
	AST ast = astRoot.getAST();
	ASTRewrite rewriter = ASTRewrite.create(ast);
 
	//for getting insertion position
	TypeDeclaration typeDecl = (TypeDeclaration) astRoot.types().get(0);
	MethodDeclaration methodDecl = typeDecl.getMethods()[0];
	Block block = methodDecl.getBody();
 
	ListRewrite listRewrite = rewriter.getListRewrite(block, Block.STATEMENTS_PROPERTY);
	Statement placeHolder = (Statement) rewriter.createStringPlaceholder("//mycomment", ASTNode.EMPTY_STATEMENT);
	listRewrite.insertFirst(placeHolder, null);
 
	TextEdit edits = rewriter.rewriteAST();
 
	// apply the text edits to the compilation unit
	Document document = new Document(unit.getSource());
 
	edits.apply(document);
 
	// this is the code for adding statements
	unit.getBuffer().setContents(document.get());
 
	System.out.println("done");
}

#It is not necessary to run the code above inside an eclipse plug-in project, but it is easier to do so.

Category >> Java Development Tools (JDT)

If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:

<pre><code> 
String foo = "bar";
</code></pre>

ak

Hi, I want to delete all comments from code(line comment,block comment and javadoc) i used BlockComment.getAlternateRoot().delete and node.delete, ASTrewrite ; but i failed.
arman

thank you for the information, Obat Diabetes we respect each other and visit each other by exchanging link..insha Allah four months
João Lopes

You think this could be used to change the superclass of a class?
João Lopes

There is no parse(..) method.

Add Comments by using Eclipse JDT ASTRewrite

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