Let’s repeat that ‘Java is not Android‘.
Many people think that because Android uses the same syntax as Java that it will run Java code. The problem is that a language consists just not of the syntax but what is built into the language. Simple Java programs will run in Android but lots of libraries are missing, especially the Swing and the Graphics2D libraries. So you would need to rewrite all your graphical code to make Java code run on Android. As rendering a PDF involves a lot of Graphics2D code, that makes converting a Java PDF viewer to Android a major task.
And that is why most Java code can not run on Android.
This post is part of our “Android Articles Index” series. In these articles, we aim to explore android in different ways. Have a look!