Java doesn't allow programmers to directly access for safety reasons. Basically with pointers you could access memory directly and alter it's state. That is like tampering with the something that a programmer shouldn't do. For instance, some of the viruses were developed to use pointers to tamper with user's memory, refer (wiki link), under heading Function pointer.
Java is developed to be a better, secured programming language. That is why. And there are some other reasons as well, but this is the important one.
