Given: public class X { private Collection collection; public void set (Collection collection) { this.collection = collection; } } and public class Y extends X { public void set (Map<String,String>…

The correct answer is B. set(map.values()); D. super.set(map.values()). Options B and D work because Map.values() returns a Collection<String>, which is assignment-compatible with the raw Collection parameter in X.set(Collection). B calls the inherited set(Collection) via the normal dispatch chain (Y inherits it from X), and D does the same thing…

Working with Arrays and Collections

Question

Given:
public class X {
private Collection collection;
public void set (Collection collection) {
this.collection = collection;
}
}
and
public class Y extends X {
public void set (Map<String,String> map) {
super.set(map); // line 1
}
}
Which two lines can replace line 1 so that the Y class compiles? (Choose two.)

Options

Amap.forEach((k, v)->set(v));
Bset(map.values());
Csuper.<String,String>map
Dsuper.set(map.values());
Eset(map)

How the community answered

(56 responses)

A
13% (7)
B
79% (44)
C
4% (2)
E
5% (3)

Explanation

Options B and D work because Map.values() returns a Collection<String>, which is assignment-compatible with the raw Collection parameter in X.set(Collection). B calls the inherited set(Collection) via the normal dispatch chain (Y inherits it from X), and D does the same thing with an explicit super. call - both pass a valid Collection to X's setter.

Why the others fail:

A (map.forEach((k, v)->set(v))) - v is a String, so set(v) looks for a set(String) method that doesn't exist in X or Y; won't compile.
C (super.<String,String>map) - Invalid syntax entirely; map is a local parameter, not a method, so this doesn't parse as a valid statement.
E (set(map)) - Inside Y's set(Map<String,String>), calling set(map) resolves back to Y's own method (Map matches Y's signature before X's Collection), causing infinite recursion. Even if it compiled, it never reaches X's setter.

Memory tip: In Java, Map is not a Collection - they are parallel interfaces under java.util. Whenever you need to bridge a Map to a Collection, reach for map.values() (Collection), map.keySet() (Set), or map.entrySet() (Set) - all three are legitimate Collections.

Topics

#inheritance#collections hierarchy#method overloading#type compatibility

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