1. Because programs written in Java language runs on a virtual machine, it runs somewhat slowly compared to other programs. However, it is unlikely that it feels annoyingly slow on today's fast computers. 2. Rather, a worse problem is that the programs do not always work correctly even if they are written correctly, because a Java virtual machine may be written incorrectly. It is difficult to write a perfect program, especially if it is as big as a virtual machine, so that programs written in Java langauge tend to suffer from slightly different problems depending on the platforms on which the Java virtual machines run.