Discussion
What will be the output of the program?
import java.util.*;
public class Listing63
{
public static void main(String[] args)
{
Map<String, List<String>> m = new HashMap<String, List<String>>();
List<String> shared = new ArrayList<String>();
m.put("x", shared);
m.put("y", shared);
m.get("x").add("v");
System.out.println(m.get("y").size() + " " + m.size());
}
}
Answer: C
Both keys were given the SAME list object, so appending through one key is visible through the other and the size reads 1. The map itself holds two entries because the keys differ. Storing a value twice stores the reference twice, never a copy.
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