CODEWITHSUNDEEP
java
Michael
Michael

Reputation: 13614

Why I get HashMap cannot be resolved to a type error?

Here is my Java code:

import java.util.HashMap;
import java.util.Map;


    public class Polynomial<K> {
        Map<Integer, Object> polynomial;

        public Polynomial(){
            polynomial = new HashMap<K, V>();
        }
        public  Polynomial(int numberOfMembers){
            polynomial = new HashMap<K, V>(numberOfMembers);
        }
        public void addElm(int power, int coefficient){
            if (power < 0) {
                power = Math.abs(power);
                throw new RuntimeException("ERROR: The power must be an absolute number, converting to absolute");
            }
            for (Map.Entry m : polynomial.entrySet()) {
                if ((Integer) m.getKey() == power){
                    polynomial.put(power,m.getValue());
                }
            }
        }

    }

On this two rows:

polynomial = new HashMap<K, V>();

and this:

polynomial = new HashMap<K, V>(numberOfMembers);

I get this error:

HashMap<K,V> cannot be resolved to a type

Any idea what cause to the error above and how to fix it?

Upvotes: 2

Views: 33774

Answers (2)

kmecpp
kmecpp

Reputation: 2479

I don't think you actually intend to use the generics you are have.

When you create a new HashMap<K,V>(), those <K,V> values are the actual class names for the types that the HashMap will hold. In your case, those types are Integer and Object so you should write new HashMap<Integer, Object>().

Even that is unnecessary however because Java can infer the type of the HashMap since you have already defined it once. It is best to just use new HashMap<>();

public class Polynomial {

    Map<Integer, Object> polynomial;

    public Polynomial() {
        polynomial = new HashMap<>();
    }

    public Polynomial(int numberOfMembers) {
        polynomial = new HashMap<>(numberOfMembers);
    }

    public void addElm(int power, int coefficient) {
        if (power < 0) {
            power = Math.abs(power);
            throw new RuntimeException("ERROR: The power must be an absolute number, converting to absolute");
        }
        for (Entry<Integer, Object> m : polynomial.entrySet()) {
            if ((Integer) m.getKey() == power) {
                polynomial.put(power, m.getValue());
            }
        }
    }

}

Upvotes: 4

Zabuzard
Zabuzard

Reputation: 25903

You write Map<Integer, Object> polynomial;. This means polynomial is a Map that needs Integer and Object but then you assign polynomial = new HashMap<K, V>();. The class K and V are not Integer and Object thus the error.

You could write

polynomial = new HashMap<Integer, Object>();

then it would work. What are the types you actually want? Why did you even wrote K, V in the first place? Or else, why the Integer, Object, why not stick to K and V? And also, if you would like to hold V generic you need to add it to class Polynomial<K, V> too.

Upvotes: 2

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