Remove entry from map without iterating

Question

How do I remove entry from Java Map without using iteration using value or key. Basically in my map, I am using containsKey() then map.remove() to remove it.

Answer 1

In most cases you can remove entry (key-value pair) from a map using Map.remove(key) method. There will be no iteration over the map. You don't need to use Map.containsKey(key) before the Map.remove(key) because Map.remove already does it. It returns either a previous associated value with key or null if there was no mapping for the key.

But you can't do the same thing using a value only (without key). The only option is to iterate via map and find entry (or entries) with that value.

Java 5-7:

for (Iterator<MyValue> it = map.values.iterator(); it.hasNext(); ) {
    if(it.next().equals(myValue)) {
        it.remove();
    }
}

Java 8:

map.values().removeIf(v -> v.equals(myValue));

Answer 2

Use Map#remove(Object key):

public V remove(Object key)

Removes the mapping for this key from this map if it is present (optional operation). More formally, if this map contains a mapping from key k to value v such that (key==null ? k==null : key.equals(k)), that mapping is removed. (The map can contain at most one such mapping.)

Returns the value to which the map previously associated the key, or null if the map contained no mapping for this key. (A null return can also indicate that the map previously associated null with the specified key if the implementation supports null values.) The map will not contain a mapping for the specified key once the call returns.

Basically you can call remove, even if the key does not exist. It will silently fail in that case(returning null). The object need not be identical or the same, if yourKey.equals(key) is true for the key you want to remove.