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Display

One of the many great things about the Jupyter front ends is the support for display_data. IJava interfaces with the base kernel's high level rendering API.

Notebook functions

IJava injects 2 functions into the user space for displaying data: display and render. Most use cases should prefer the former but there is a necessary case for render that is outline below. In addition the updateDisplay function can be used to update a previously displayed object. All are defined in the runtime Display class.

All display/render functions include a text/plain representation in their output. By default this is the String.valueOf(Object) value but it can be overridden.

String display(Object o)

Display an object as it's preferred types. If you don't want a specific type it is best to let the object decide how it is best represented.

The object is rendered and published on the display stream. An id is returned which can be used to updateDisplay if desired.

String display(Object o, String... as)

Display an object as the requested types. In this case the object attempts to be rendered as the desired mime types given in as. No promises though, if a type is unsupported it will simply not appear in the output.

The object is rendered and published on the display stream. An id is returned which can be used to updateDisplay if desired.

This is useful when a type has many potential representations but not all are preferred. For example a CharSequence has many representations but only the text/plain is preferred. To display it as executable javascript we can use the following:

display("alert('Hello from IJava!');", "application/javascript");

Since there is the potential that some front ends don't support a given format many can be given and the front end chooses the best. For example, to display as html and markdown:

display("<b>Bold</b>", "text/html", "text/markdown");

This will trigger a display message with values for text/html, text/markdown, and the implicit text/plain.

DisplayData render(Object o)

Renders an object as it's preferred types and returns it's rendered format. Similar to display(Object o) but without publishing the result.

DisplayData render(Object o, String... as)

Renders an object as the requested types and returns it's rendered format. Similar to display(Object o, String... as) but without publishing the result.

When expressions are the last code unit in a cell they are rendered with the render(Object o) semantics. If this is not desired it can be hijacked by wrapping it in a call to this function.

String md = "Hello from **IJava**";

render(md, "text/markdown")

This will result in the Out[_] result to be the pretty text/markdown representation rather than the boring text/plain representation.

void updateDisplay(String id, Object o)

Renders an object as it's preferred types and updates an existing display with the given id to contain the new rendered object. Similar to display(Object o) but updates an existing displayed object instead of appending a new one.

void updateDisplay(String id, Object o, String... as)

Renders an object as it's requested types and updates an existing display with the given id to contain the new rendered object. Similar to display(Object o, String... as) but updates an existing displayed object instead of appending a new one.

String id = display("<b>Countdown:</b> 3", "text/html");
for (int i = 3; i >= 0; i--) {
    updateDisplay(id, "<b>Countdown:</b> " + i, "text/html");
    Thread.sleep(1000L);
}
render("<b>Liftoff!</b>", "text/html")