Question

Which of the following methods will compile without error?

public int add(List<? extends Number> list) {
int sum = 0;
for (Integer i : list) sum += i;
return sum;
}

public int add(List<? super Integer> list) {
int sum = 0;
for (Integer i : list) sum += i;
return sum;
}

public int add(List<? extends Integer> list) {
int sum = 0;
for (Integer i : list) sum += i;
return sum;
}

public int add(List<?> list) {
int sum = 0;
for (Integer i : list) sum += i;
return sum;
}

Answer 1

public int add(List<? extends Integer> list) {
int sum = 0;
for (Integer i : list) sum += i;
return sum;
}
Because only in this method is a valid class cast