import java.util.ArrayList;
import java.util.List;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		BarManager bm = new BarManager();
		System.out.println(bm.get());
	}
}
 
class BarManager {
	private List<Integer> bars;
 
	BarManager() {
		// build using a mutable list, make an immutable copy when done
		ArrayList<Integer> bars = new ArrayList<>();
		bars.add(1);
		bars.add(2);
		bars.add(3);
		this.bars = List.copyOf(bars);
	}
 
	public List<Number> get() {
		return List.copyOf(bars); // does not actually copy
	}
}
 

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