Base Language
The BaseLanguage is an MPS' counterpart to Java, since it shares with Java almost the same set of constructs. BaseLanguage is the most common target of code generation in MPS and the most extensively extended language at the same time.
In order to simplify integration with Java, it is possible to specify the classpath for all modules in MPS. Classes found on the classpath will then be automatically imported into @java_stub models and so can be used directly in programs that use the BaseLanguage.
The frequently extended concepts of MPS include:
Expression. Constructs, which are evaluated to some results like 1, "abc", etc.
Statement. Constructs, which can be contained on a method level like if/while/synchronized statement.
Type. Types of variables, like int, double.
IOperation. Constructs, which can be placed after a dot like in node.parent. The parent element is a IOperation here.
AbstractCreator. Constructs, which can be used to instantiate various elements.
Although, BaseLanguage was originally created using the Java 6 specification, it now includes features like try with resources, catch multiple exceptions, local variable type inference, default and private interface methods or the diamond operator from later Java versions. No additional language import is required to use these features since they are part of BaseLanguage itself. To provide compatibility with build processes requiring certain java language level, each solution can be configured in the Java tab of the module properties dialog to prohibit language feature not compatible with required language level.
Javadoc
Just like Java, BaseLanguage supports documentation comments in the javadoc style. The jetbrains.mps.baseLanguage.javadoc language must be imported for javadoc to be available. You insert a fresh skeleton of a javadoc comment either by an intention called "Add Documentation Comment" or by typing "/**" in front of a method or a (static) field declaration.
While editing a javadoc comment, side transformations as well as intentions are available to create inline and block tags (e.g. @author, {@link ...}, etc.), html markup or code snippets.
Since javadoc uses jetbrains.mps.lang.text under the hood, the editing experience is the same as in other "textual" languages in MPS. You can apply styles (e.g. bold) and formatting (e.g. header, bullet point, etc.). Copy/paste between these "textual" languages also works smoothly. See the documentation of the text language editing for more details on the subject.
Import textual Java
To help the users bridge the gap between textual Java and projectional BaseLanguage, several contextual actions are available in the pop-up menu when editing BaseLanguage code that can paste Java code from the clipboard. These actions trigger the built-in Java parser and insert projectional code that represents the original Java code using the concepts of BaseLanguage.
Paste as Java Class Content - parses the text from the clipboard and pastes it into a class/interface/enum definition and methods, fields and nested classes.
Paste as Java Statements - parses the text from the clipboard and pastes it into a BaseLanguage method as its body.
Paste as JavaDoc - parses the text from the clipboard and pastes it into a javadoc comment at the current position of the cursor. If the cursor is not positioned within an existing javadoc comment, the action attaches the parsed javadoc to the following field/method/class definition’s javadoc, creating a new javadoc for them, if needed.