Why can't I clone ConcurrentHashMap?
ConcurrentHashMap<String, String> test = new ConcurrentHashMap<String, String>();
test.put("hello", "Salaam");
ConcurrentHashMap<String, String> test2 = (ConcurrentHashMap<String, String> ) test.clone();
System.out.println(test2.get("hello"));
If I use HashMap instead of ConcurrentHashMap, it works.
The clone() method on AbstractMap is not meant for copying, it is an internal method, note the protected keyword.
protected Object clone() throws CloneNotSupportedException {
HashMap happens to have a public clone(), but this does not mean you should use it, this is discussed further by Effective Java: Analysis of the clone() method
A more flexible way to create copies of collections is via the copy-constructors. These have advantage of creating any Map implementation from any other.
/**
* Creates a new map with the same mappings as the given map.
*
* @param m the map
*/
public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
e.g.
ConcurrentHashMap<String, String> original = new ConcurrentHashMap<String, String>();
original.put("hello", "Salaam");
Map<String, String> copy = new ConcurrentHashMap<>(original);
original.remove("hello");
System.out.println(copy.get("hello"));