Polymorphism

AP Computer Science A· difficulty 3/5

ArrayList<Object> list = new ArrayList<Object>();
list.add("hello");
list.add(42);
list.add(3.14);
int count = 0;
for (int i = 0; i < list.size(); i++) {
    if (list.get(i) instanceof String) count++;
}
System.out.print(count);

What is printed?

A
$2$
B
$0$
C
$3$
D
$1$
check_circle

Explanation

Only "hello" is a String. 42 autoboxes to Integer, 3.14 to Double. So instanceof String is true exactly once.

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