In Java, you can use collections.shuffle to clean or rerun a ArrayList

TestApp.java

package com.mkyong.utils;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class TestApp {

    public static void main(String[] args) {

        List<String> list = Arrays.asList("A", "B", "C", "D", "1", "2", "3");

        //before shuffle
        System.out.println(list);

        // again, same insert order
        System.out.println(list);

        // shuffle or randomize
        Collections.shuffle(list);
        System.out.println(list);
        System.out.println(list);

        // shuffle again, different result
        Collections.shuffle(list);
        System.out.println(list);

    }

}

Output

[A, B, C, D, 1, 2, 3]
[A, B, C, D, 1, 2, 3]

[2, B, 3, C, 1, A, D]
[2, B, 3, C, 1, A, D]

[C, B, D, 2, 3, A, 1]

References

Collections.shuffle JavaDoc