cannot be cast to java.lang.Comparable

I faced a similar kind of issue while using a custom object as a key in Treemap. Whenever you are using a custom object as a key in hashmap then you override two function equals and hashcode, However if you are using ContainsKey method of Treemap on this object then you need to override CompareTo method as well otherwise you will be getting this error Someone using a custom object as a key in hashmap in kotlin should do like following

 data class CustomObjectKey(var key1:String = "" , var 
 key2:String = ""):Comparable<CustomObjectKey?>
 {
override fun compareTo(other: CustomObjectKey?): Int {
    if(other == null)
        return -1
   // suppose you want to do comparison based on key 1 
    return this.key1.compareTo((other)key1)
}

override fun equals(other: Any?): Boolean {
    if(other == null)
        return false
    return this.key1 == (other as CustomObjectKey).key1
}

override fun hashCode(): Int {
    return this.key1.hashCode()
} 
}

• the object which implements Comparable is Fegan.

The method compareTo you are overidding in it should have a Fegan object as a parameter whereas you are casting it to a FoodItems. Your compareTo implementation should describe how a Fegan compare to another Fegan.

• To actually do your sorting, you might want to make your FoodItems implement Comparable aswell and copy paste your actual compareTo logic in it.