cannot be cast to java.lang.Comparable

Question

import java.util.HashMap; import java.io.*; import java.util.*; public class Fegan implements Comparable{ HashMap<String, Integer> cart = new HashMap<String, Integer>(); List list = new ArrayList<FoodItems>(); int x =0; public void addToCart(FoodItems f) {     cart.put(f.name, f.valueOfFood); } public String display(FoodItems f) {     return(f.name + " costs " + f.valueOfFood); } public void addToList(FoodItems f) {     //FoodItems temp = (FoodItems) f;     list.add(f); } public int compareTo(Object o) {     //FoodItems temp = (FoodItems) o;     if(this.x == ((FoodItems)o).valueOfFood)         return 0;     else if (this.x <((FoodItems)o).valueOfFood)         return 1;     else          return -1; } public void sortMap(List list) {     for(int i =0; i< list.size(); i++)     {         FoodItems temp = (FoodItems) list.get(i);         cart.put(temp.name, temp.valueOfItem);      } } } 

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import java.util.Collections; import java.util.HashMap; import java.util.Iterator; import java.io.*; import java.util.*; public class Test { public static void main(String [] args) {     HashMap<String, Integer> cart = new HashMap<String, Integer>();     FoodItems firts = new FoodItems("Chocolate" , 50);     FoodItems second = new FoodItems("Juice", 79);     FoodItems third = new FoodItems("Apple", 200);     FoodItems forth = new FoodItems("Orange", 300);     FoodItems fifth = new FoodItems("Milk" , 400);     ArrayList items = new ArrayList();     items.add(firts);     items.add(second);     items.add(third);     items.add(forth);     items.add(fifth);     Collections.sort(items);     Iterator itr = items.iterator();     Fegan myFegan = new Fegan();     myFegan.sortMap(items);      while(itr.hasNext()){         Object element = itr.next();         System.out.println(element + "\n");     } } } 

Why it is writing:

Exception in thread "main" java.lang.ClassCastException: FoodItems cannot be cast to java.lang.Comparable at java.util.ComparableTimSort.countRunAndMakeAscending(Unknown Source) at java.util.ComparableTimSort.sort(Unknown Source) at java.util.ComparableTimSort.sort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at Test.main(Test.java:21) 

Answer 1

• 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.