Use random.nextInt(range-1)
and then map that number to the output number with a function that excludes the previous number:
public class Test {
private final Random random = new Random();
private final int range;
private int previous;
Test(int range) { this.range = range; }
int nextRnd() {
if (previous == 0) return previous = random.nextInt(range) + 1;
final int rnd = random.nextInt(range-1) + 1;
return previous = (rnd < previous? rnd : rnd + 1);
}
public static void main(String[] args) {
final Test t = new Test(4);
for (int i = 0; i < 100; i++) System.out.println(t.nextRnd());
}
}