Creating a random exercise in Android eclipse

Hi everybody, i have this exercise and i need help, how i can create this in android: I have 6 buttons with a cat image on it

then i want a random that set a fb image in 1 button so by default the other 5 buttons must have a twitter images.

so when run the program and if i press one button the button change to the fb image or to the twitter images

note: the random is because the fb image cant be in the same place, so can be hard to find

thank you!