/*******************************************************************************
 * Copyright (c) 2006, 2007 Oracle. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0, which accompanies this distribution
 * and is available at http://www.eclipse.org/legal/epl-v10.html.
 * 
 * Contributors:
 *     Oracle - initial API and implementation
 ******************************************************************************/
package org.eclipse.jpt.core.internal.jdtutility;

import org.eclipse.jdt.core.dom.AST;
import org.eclipse.jdt.core.dom.Expression;
import org.eclipse.jdt.core.dom.StringLiteral;

/**
 * Convert a string literal to/from a string (e.g. "text").
 */
public final class StringExpressionConverter
	extends AbstractExpressionConverter<String>
{
	private static ExpressionConverter<String> INSTANCE;

	/**
	 * Return the singleton.
	 */
	public static ExpressionConverter<String> instance() {
		if (INSTANCE == null) {
			INSTANCE = new StringExpressionConverter();
		}
		return INSTANCE;
	}

	/**
	 * Ensure single instance.
	 */
	private StringExpressionConverter() {
		super();
	}

	@Override
	protected StringLiteral convertObject(String string, AST ast) {
		StringLiteral stringLiteral = ast.newStringLiteral();
		stringLiteral.setLiteralValue(string);
		return stringLiteral;
	}

	@Override
	protected String convertExpression(Expression expression) {
		Object value = expression.resolveConstantExpressionValue();
		return (value instanceof String) ? (String) value : null;
	}

}