We can check the type of property(whether single or multiple) using the method isMultiple() of Property interface. Below is an example to check the node property "items" is a single value or multiple values and based on that get the value or values for that property in AEM.
Property property = node.getProperty("items");Value[] values = null;if(property.isMultiple()){values = property.getValues();} else {values[0] = property.getValue();}
Hope this helps. Thank you!