MyClass.java
 

import java.util.ArrayList;
import java.util.Collections;

public class MyClass { 
  public static void main(String[] args) { 
    ArrayList<Integer> myNumbers = new ArrayList<Integer>();
    myNumbers.add(33);
    myNumbers.add(15);
    myNumbers.add(20);
    myNumbers.add(34);
    myNumbers.add(8);
    myNumbers.add(12);

    Collections.sort(myNumbers);

    for (int i : myNumbers) {
      System.out.println(i);
    }
  } 
}

Result:
8
12
15
20
33
34