public static void redo() {
if (currentState == null) {
return;
}
if (currentState.next == tail) {
return;
}
currentState = currentState.next;
gotoState(currentState.content);
}
public static void undo() {
if (currentState == null) {
return;
}
if (currentState.prev == head) {
return;
}
currentState = currentState.prev;
gotoState(currentState.content);
}
