Class Diagrams for activemq-4.0-M4 source code.
These diagrams cover the bulk of the source code and are in EMF format.
Note about conversion to other formats: Some files when converted to something like JPG or PNG will be quite large. If your system doesn't have enough RAM you will get an error or in some cases the converting program will just scale to fit which usually will mangle the image. For the larger file conversions you will need 1GB of RAM. A free program I came across for converting is IrfanView (http://www.irfanview.com/). I found it much better than Windows Image Viewer, but you still need an appropriate amount of memory.
Note about printing: Adobe In Design works well for printing if you want a large print but don't have access to an oversized/wide format ink jet (http://www.adobe.com/products/tryadobe/main.jsp#product=31). Set up the page dimensions first, for example, normal letter size page is measured in pts, 51p0 width, 66p0 height. So for a wider than long oversized diagram you might go to File->Document Setup... and set Page Size to "Custom" and width to 255p0 (5 8 1/2" letter pages in width), and height to 112p0 (2 11" letter pages in height). Next go to File->Place... to import the EMF. Using the Scale tool (smaller box with an arrow pointing into larger box) size the image to fit inside the page (hold down shift key while sizing to keep proportions), and position it using the Selection tool (arrow).
Then go to File->Print..., select "Setup" and check the "Tile" option. The "Tile" dropdown setting should be "Auto" and Overlap 4p0. Then set the Scale option to a percentage that maximizes the image coverage (there is a visual thumbnail that will indicate the coverage). Then Print. This should yield a nice large image printed out in tiled format on letter size pages. Each page will be properly numbered so you know their positions, and there will be marks for trimming and taping the pages together. A page cutter is neccessary. Just trim the right and bottom overlap on each page, then align and tape.