遍历哈希表并使用get和containsKey方法

Question

Having trouble with the containsKey and get method, also not sure how to iterate through the hashtable keys and values, I want to iterate through and add the keys with the value of true to the solution list

1st error: The method containsKey(int) is undefined for the type hashTable

2nd error: Can only iterate over an array or an instance of java.lang.Iterable

3rd error: The method get(int) is undefined for the type hashTable

  package practice;

        import java.util.*;
        /*

        You are given an integer array, where all numbers except for TWO numbers appear even number of times. 

        Q: Find out the two numbers which appear odd number of times.

        */

        public class hashTable{
        public static void main(String[] args){
            int[] test = {2, 2, 5, 7, 4, 4};
            List<Integer> solution = new ArrayList<Integer>();
            Hashtable<Integer, Boolean> ht = new Hashtable<Integer, Boolean>(); 
            Boolean check = true;
            for (int item : test){
//error             if (!containsKey(item)){
                    check = true;
                } else{
                    check = false;
                    ht.put(item, check);

                }
                }

//error            for (int item : ht){
//error             if (get(item) == true){
                    solution.add(item);
                }
                }
            System.out.println("the result is");
            System.out.println(solution);
            }

         }

Answer 1

The issue would seem that you are using a generic type without providing the generic information. If you put @SuppressWarnings("unchecked") (or something along those lines, do not have an IDE to test), the warning should go away. That being said, I would advise against that.

Ideally, you should provide generic information and do as @BackSlash suggested: Hashtable<Integer, String> ht = new Hashtable<Integer, String>(); . This will provide the compiler with the generic information it needs and makes your collection type safe which is something you usually want.

That being said, I would recommend a different approach:

1. Iterate over your array.
2. Create a hash table: HashTable<Integer, Boolean> .
3. If the number you are iterating on exists in the hash table, then apply the not operator on the value at HashTable[number] .
4. If not, add a new entry and set the boolean value to false.

Seeing your comment, you could try something like so:

Hashtable<Integer, Boolean>  table = new Hashtable<Integer, Boolean>();
int[] nums = ...
for(Integer number : nums)
{
    if(table.containsKey(number))
    {
        table.put(number, !table.get(number));
    }
    else
    {
        table.put(number, false);
    }
}