Java Memory Playground Studio

Edit .jmp files — diagrams of the Java stack and heap — visually, inside VS Code.

Open a .jmp file and the diagram opens instead of the JSON: build objects, drag references between them, push and pop stack frames, and step through a trace. It is the same editor as jmp.openpatch.org, with the teacher's tools on.

Getting started

• Java Memory Playground: New Diagram creates a .jmp file and opens it.
• Opening any .jmp file shows the diagram.
• Show Source switches to the JSON; Show Diagram switches back.

Saving

The diagram is the file. Every edit goes straight into the document, so the tab picks up its unsaved dot, Ctrl+S saves as usual, and the editor's own undo works on the file the way it does anywhere else.

The playground's own Ctrl+S is unbound here, because VS Code already owns it.

Classes from Java source

The config view takes the classes as Java rather than asking for each field through a dialog:

class Node {
    int value;
    Node next;
}

Only the structure is read — class names, and the name and type of each field. Method bodies are skipped and nothing is executed.

The file format

A .jmp file is JSON, the same shape the playground puts in a shared link, so a diagram moves between the app, an embedded playground and this editor unchanged. It is a normal text file: diffable, reviewable, and fine to keep in a repository next to the code it illustrates.

Keyboard shortcuts

License

MIT