How to check if aspecified object exists in a given list of object or not with java

Question

I am using java 11 and i want to check if a object exist in list of object i use

   List<MenuDTO> menuDTO=new ArrayList<>();
   MenuDTO menu=menuData.findByIdMenu(menuItemDTO.getMenuid());

   if(menuDTO.contains(menu)){
                    menuItemResult.add(menuItemDTO);
                    menu.setMenuitems(menuItemResult);
   }

But it return always false even the list contain the element

Answer 1

I don't know if this is what you are looking for, but maybe this can help:

List<MenuDTO> menuDTO=new ArrayList<>();
MenuDTO menu=menuData.findByIdMenu(menuItemDTO.getMenuid());
boolean doesExists = menuDTO.stream().anyMatch(menuElement -> menuElement.getMenuId() == menu.getMenuId());
if(doesExists){
    menuItemResult.add(menuItemDTO);
    menu.setMenuitems(menuItemResult);
}
 

Answer 2

Java collections contains use object equals methods to determine if specified object is in the collection, so you need to implement it for objects that you use in collections. Here is some guide on how to implement equals and hashCode methods on objects:

Java equals() and hashCode() Contracts