Return value of method

Hi, How do i write a statement that checks the return value of a method in java. I have to do a conditional action based on the return value of true or false.
How do i put this in an If statement and a while loop.
Thanks

Here's a small example: filling an array with unique numbers.

Code:

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import java.util.*;

public class LoopTesting {
    public static void main(String[] args) {
        Random rand = new Random();
        int seed = 20;
        int count = 0;
        int[] vals = new int[10];
        // Initialize elements with -1 to avoid value of zero.
        Arrays.fill(vals, -1);
        // Fill the vals array with unique numbers [0 - 19].
        while(count < vals.length) {
            int next = rand.nextInt(seed);
            if(isUnique(next, vals))
                vals[count++] = next;
        }
        System.out.printf("vals = %s%n", Arrays.toString(vals));
    }

    private static boolean isUnique(int n, int[] array) {
        for(int j = 0; j < array.length; j++) {
            if(array[j] == n)
                return false;
        }
        return true;
    }
}

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