AbstractMap

import java.security.PublicKey;
import java.util.Iterator;
import java.util.Map;

public abstract class AbstractMap<K,V> implements Map<K,V> {
    public boolean isEmpty() {
        return size() == 0;
    }

    protected static class MapEntry<K, V> implements Entry<K, V> {
        private K k;
        private V v;

        public MapEntry(K key, V value) {
            k = key;
            v = value;
        }

        public K getKey() {
            return k;
        }

        public V getValue() {
            return v;
        }

        protected void setKey(K key) {
            k = key;
        }

        protected V setValue(V value) {
            V old = v;
            v = value;
            return old;
        }
    }

    private class KeyIterator implements Iterator<K> {
        private Iterator<Entry<K, V>> entries = entrySet().iterator();

        public boolean hasNext() {
            return entries.hasNext();


        }
        public K next(){
            return entries.next().getKey();
        }
        public void remove(){
            throw new UnsupportedOperationException();
        }
        private class  ValueIterable implements Iterable<V>{
            public Iterator<V>iterator(){
                return new ValueIterator();
            }
            public Iterable<V> values(){
                return new ValueIterable();
            }
        }
    }
}