Hack #1 - Recursion

public void drawLine(int n) {
    for (int i = 1; i <= n; i++) {
        System.out.print("*");
    }
    if(n > 0){
        System.out.println();
        drawLine(n - 1);
    }
}
drawLine(10);

**********
*********
********
*******
******
*****
****
***
**
*

Hack #2 - Sorting

import java.util.ArrayList;
import java.util.Comparator;

public class Country {
    private String name;
    private int size;

    public Country(String name, int size) {
        this.name = name;
        this.size = size; // in million miles ^2
    }

    public String getName() {
        return name;
    }

    public int getSize() {
        return size;
    }

    public static void main(String[] args) {
        ArrayList<Country> countries = new ArrayList<>();
        countries.add(new Country("USA", 3797));
        countries.add(new Country("Russia", 6602));
        countries.add(new Country("China", 3702));
        countries.add(new Country("Canada", 3855));

        // Print the unsorted countries
        System.out.println("Unsorted:");
        for (Country country : countries) {
            System.out.print(country.getName() + ": " + country.getSize() + ", ");
        }
        System.out.println("");

        // Sort the countries in decreasing order based on their size
        countries.sort(new Comparator<Country>() {
            @Override
            public int compare(Country c1, Country c2) {
                // Compare the sizes in descending order
                return Integer.compare(c2.getSize(), c1.getSize());
            }
        });

        // Print the sorted countries
        System.out.println("Sorted:");
        for (Country country : countries) {
            System.out.print(country.getName() + ": " + country.getSize()  + ", ");
        }
    }
}

Country.main(null)

Unsorted:
USA: 3797, Russia: 6602, China: 3702, Canada: 3855, 
Sorted:
Russia: 6602, Canada: 3855, USA: 3797, China: 3702,

Hack #3 - Arraylists

public class Compare{
    public boolean compareArrayLists(ArrayList<Integer> list1, ArrayList<Integer> list2){
        if(list1.size() != list2.size()){
            return false;
        }
        for(int i=0; i < list1.size(); i++){
            if(list1.get(i) != list2.get(list2.size()-i-1)){
                return false;
            }
        }
        return true;
    }

    public void delete(ArrayList<Integer> list1){
        int int1 = list1.get(0);

        for(int i = 0; i < list1.size(); i++){
            if (i !=0){
                list1.remove(i);
            }
        }
    }

    public static void main(String[] args){
        Compare compare = new Compare();

        ArrayList<Integer> list1 = new ArrayList<Integer>();
        list1.add(1);
        list1.add(2);
        list1.add(3);
        list1.add(4);
        list1.add(5);
        list1.add(6);
        list1.add(7);


        ArrayList<Integer> list2 = new ArrayList<Integer>();
        list2.add(7);
        list2.add(6);
        list2.add(5);
        list2.add(4);
        list2.add(3);
        list2.add(2);
        list2.add(1);

        System.out.println(list1);
        System.out.println(list2);

        System.out.println("Reversed - " + compare.compareArrayLists(list1,list2));
        compare.delete(list1);
        System.out.println(list1);
    }
}

Compare.main(null);

[1, 2, 3, 4, 5, 6, 7]
[7, 6, 5, 4, 3, 2, 1]
Reversed - true
[1, 3, 5, 7]