Thread: how to write generated numbers in a file without repeatition

import java.util.ArrayList;
import java.util.Random;
import java.io.FileWriter;
import java.io.BufferedWriter;
import java.io.IOException;
 
public class Test {
 
    public static void main(String[] args)throws IOException {
        int size = 100;
 
        ArrayList<Integer> list = new ArrayList<Integer>(size);
        for(int i = 1; i <= size; i++) {
            list.add(i);
        }
 
        Random rand = new Random(System.currentTimeMillis());
        while(list.size() > 60) {
            int num = rand.nextInt(list.size());
            BufferedWriter writer = new BufferedWriter(new FileWriter("C:\\Users\\glenn\\Desktop\\trial.txt",true)); // with existing data
            writer.write(list.remove(num)+ " ");
            writer.newLine();
            writer.close();   
       } 
   }
}

hi to everyone, im a beginner in java , i need some help of you guys if any,
i intend to write a generated numbers without repeatition, and my problem is,
if i write it in file with existing data on it... repeatition of numbers occurs ....

Thanks, can u give me code samples on how it look like,? for me to develop this code.