Storing non-duplicated numbers in an array

Overview: My program has to store 20, non-duplicated randomly generated numbers from a range of 1 to 100 in an array. Problem: If I find a match(duplicated #) in the inner for loop, I flag the boolean variable. Here is what I don't know how to do. After the for loop, if the boolean hasn't been flagged, I want to add the random number to the array. I also want to increment x (until I have 20 non-duplicated numbers stored) but only if I add the element to the array.

public void duplication(){
    int max = 100; // max value for range
    int min = 1; // min value for range
    boolean duplicate = false;
    Random rand = new Random();

    for (int x = 0; x < 20; x++){
        //initiates array that stores 20 values
        int[] all = new int[20];
        //generates # from 1-100
        int randomNum = rand.nextInt((max - min) + 1) + min;
        all[x] = randomNum;
        //iterates through array
        for (int i : all) {
            //if there's a match (duplicate) flag boolean
            if (i == randomNum){
                duplicate = true;
            }
            else {
                duplicate = false;
            }
        }
    }
    //if boolean hasn't been flagged
    if (duplicate=false){
        //store to array
    }
}