Back and forward implementation

History.java

import java.util.ArrayDeque;
import java.util.Deque;

public class History<ENTITY> {

    private Deque<ENTITY> backStack = new ArrayDeque<>();
    private Deque<ENTITY> forwardStack;
    private ENTITY current;
    private int max;

    public History(int max) {
        this.max = max;
    }

    public void record(ENTITY entity) {
        if (backStack.size() >= max) {
            backStack.pollFirst();
        }

        if (!entity.equals(current)) {
            current = entity;
            backStack.add(entity);
            forwardStack = new ArrayDeque<>();
        }
    }

    public ENTITY back() {
        ENTITY back = backStack.pollLast();
        if (back != null) {
            forwardStack.add(current);
        }
        if (current.equals(back)) {
            back = backStack.pollLast();
        }
        if (back != null) {
            current = back;
        }
        return back;
    }

    public ENTITY forward() {
        ENTITY forward = forwardStack.pollLast();
        if (forward != null) {
            backStack.add(current);
        }
        if (current.equals(forward)) {
            forward = forwardStack.pollLast();
        }
        if (forward != null) {
            current = forward;
        }
        return forward;
    }
}