如何随机生成数组中的数字，每个数字都是唯一的

I hav a numeric array,which contains 20 elements.I am displaying the numbers randomly for a blackberry application,bt i want dat all d numbers generated should b unique.It should b randomly generated,bt it has b unique until all the elemnts in the array is exhausted.I am giving the piece of code here,if anyone can help me out,i will b extremely grateful.I hav a numeric array,which contains 20 element