Insert/Add Statements to Java Source Code by using Eclipse JDT ASTRewrite

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This belongs to Eclipse JDT Tutorial Series.

This code example is for inserting a statement to existing Java source code by using eclipse JDT. It works inside of a Plug-in.

For simplicity purpose, the following code simple add a method invocation statement called “add” to the first line of a method.

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

The code above becomes the following:

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

Again, this is a completely working code tested under Eclipse Indigo.

	private void AddStatements() 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();
 
		// create new statements for insertion
		MethodInvocation newInvocation = ast.newMethodInvocation();
		newInvocation.setName(ast.newSimpleName("add"));
		Statement newStatement = ast.newExpressionStatement(newInvocation);
 
		//create ListRewrite
		ListRewrite listRewrite = rewriter.getListRewrite(block, Block.STATEMENTS_PROPERTY);
		listRewrite.insertFirst(newStatement, 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());
	}

3 thoughts on “Insert/Add Statements to Java Source Code by using Eclipse JDT ASTRewrite”

  1. I don’t understand exactly what you mean. Can you give me an example which shows your input and your expected output?

  2. Hi,
    I need to add some strings and also an if-else that whenever the condition is right some part of the original code is executed do you think that the code here could help?
    could you please guide me?

  3. I get a “The method parse(ICompilationUnit) is undefined for the type Main” message.
    Where Main is the name of my class and java file (Main.java).
    How could I fix it?

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