To generate random numbers in java, you can use the random module.

a$)$ A random integer number between $20$ and $80($inclusive$).$

b$)$ A random integer number between $-20$ and $20($inclusive$).$

c$)$ A random integer number between $-50$ and $-20($inclusive$).$

d$)$ A random floating$-$point number between $0\mathrm{.}0$ and $21\mathrm{.}9999($inclusive$).$