public class LazarHelper {
    private ArrayList<String> vidime;

    public LazarHelper() {
        vidime = null;
    }

    public ArrayList<String> getObject() {
        return this.vidime;
    }

    public void setObject(ArrayList<String> newObject) {
        this.vidime = newObject;
    }
}

public static void main(String argc, String[] *argv) {
    LazarHelper testSample = new LazarHelper();
    testSample.getObject(); //Ovde je null
    randomMethod(testSample);
    ArrayList<String> ovdeSeIDaljeVidi = testSample.getObject();
    System.out.println(ovdeSeIDaljeVidi.get(0));
}

public static void randomMethod(LazarHelper lazarHelperInstance) {
    ArrayList<String> ovoNestaje = new ArrayList<String>();
    ovoNestaje.add("TEST");
    lazarHelperInstance.setObject(ovoNestaje);
}