Java read at-most-once map

Is there an implementation of java.util.Map that only allows a value to be read once? What I'd like to do is something like this:

Map map = new ReadOnceMap();
map.put("key", "value")
System.out.println(map开发者_JAVA技巧.get("key")); // prints "value"
System.out.println(map.get("key")); // prints null

EDIT: requirements:

• existing implementation
• values are guaranteed to be read at most one time

---

map.remove() should give you the behaviour you want

Map map = new ReadOnceMap();
map.put("key", "value")
System.out.println(map.remove("key")); // prints "value"
System.out.println(map.remove("key")); // prints null

---

Something like this?

public class GetOnceHashMap<K,V> extends HashMap<K,V> {
    @Override
    public V get(Object key) {
        return remove(key);
    }

    @Override
    public Collection<V> values() {
        Collection<V> v = new ArrayList<V>(super.values());
        clear();
        return v;
    }

    @Override
    public Set<Map.Entry<K, V>> entrySet() {
        Set<Map.Entry<K, V>> e = new HashSet<Map.Entry<K,V>>(super.entrySet());
        clear();
        return e;
    }
}

---

Just call the remove() method instead of the get() method. The remove() method returns the object being removed from the map. So, the first time you'll get your object and after that it will return null.

---

Here's an implementation I came up with.

NOTE: This is not really production-quality because I'm counting on new ArrayList and new HashSet to eagerly (not lazily) read the values. To make this production quality, I would get rid of inheritance and use a dynamic proxy or object composition.

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class ReadOnceMap<K, V> extends HashMap<K, V> {

    @Override
    public V get(Object key) {
        return remove(key);
    }

    @Override
    public Set<Map.Entry<K, V>> entrySet() {
        Set<Map.Entry<K, V>> entrySet = new HashSet<Map.Entry<K, V>>(super.entrySet());
        clear();
        return entrySet;
    }

    @Override
    public Collection<V> values() {
        Collection<V> values = new ArrayList<V>(super.values());
        clear();
        return values;
    }
}