The problem is that when width (of type double) is greater than Float.MAX_VALUE, then the cast

    (float) width

results in Float.POSITIVE_INFINITY. This is what happens in TextFlow.java on line 227 (method computePrefHeight(double)):

    layout.setWrapWidth((float)wrappingWidth);

So this sets the wrapWidth in PrismTextLayout.java to infinity. Later, in PrismTextLayout.layout(), there is

    float fullWidth = Math.max(wrapWidth, layoutWidth); // fullWidth is now Infinity
    // ...
    align = 0;
    // ...
    float lineX = (fullWidth - [...]) * align; // lineX is now NaN (Infinity*0)
    // ...
    float runX = lineX; // runX is now NaN
    // ...
    run.setLocation(runX, lineY);

So we have a TextRun whose location's x coordinate is NaN. Now, I don't have an example that demonstrates this bug using only the public API, but I have one that uses non-public API, namely PrismTextLayout.getCaretShape(). These lines from the getCaretShape() method cause the propagation of the NaN value to path elements of the caret shape, making them unusable.

    Point2D location = run.getLocation();
    lineX = location.x + [...]; // lineX is now NaN
    // ...
    result[0] = new MoveTo(lineX, lineY);
    result[1] = new LineTo(lineX, lineY + lineHeight);
    return result;

I guess that depending on how this is fixed, it may also affect this advice in TextFlow's Javadoc:

    "If no wrapping is desired, the application can either set the preferred with to Double.MAX_VALUE or Region.USE_COMPUTED_SIZE."

Namely, I'm concerned about the use of Double.MAX_VALUE, or anything greater than Float.MAX_VALUE.