How to implement a dropdown menu that supports multiple selections

I want to implement a dropdown menu similar to combobox, but with the option to select multiple contents. How can I achieve this

I tried the following methods and found that they couldn't unfold as expected

omboBox combobox = new ComboBox(retnumber, retname, new ArrayList()); combobox.setId(arg0);			
combobox.setColumnName(AttributeDataUtilityHelper.getColumnName(arg0, arg1, arg2));
combobox.setMultiSelect(true);
combobox.setSelected("00");
guicomponentarray.addGUIComponent(combobox);