Given the code fragment: String[] strs = new String[2]; int idx = 0; for (String s : strs) { strs[idx].concat(" element " + idx); idx++; } for (idx = 0; idx < strs.length; idx++) {…

The correct answer is D. A NullPointerException is thrown at runtime. Option D is correct because new String[2] initializes both array slots to null by default, and calling .concat() on strs[idx] (which is null) at the first loop iteration immediately throws a NullPointerException - you cannot invoke instance methods on a null reference. A and B…

Creating and Using Arrays

Question

Given the code fragment:
String[] strs = new String[2];
int idx = 0;
for (String s : strs) {
strs[idx].concat(" element " + idx);
idx++;
}
for (idx = 0; idx < strs.length; idx++) {
System.out.println(strs[idx]);
}
What is the result?

Options

AElement 0 Element 1
BNull element 0 Null element 1
CNull Null
DA NullPointerException is thrown at runtime.

How the community answered

(28 responses)

A
4% (1)
B
11% (3)
C
4% (1)
D
82% (23)

Explanation

Option D is correct because new String[2] initializes both array slots to null by default, and calling .concat() on strs[idx] (which is null) at the first loop iteration immediately throws a NullPointerException - you cannot invoke instance methods on a null reference.

A and B are wrong for two reasons: the NPE is thrown before any print statement is reached, and even if it weren't, String.concat() returns a new String rather than modifying the original - so strs[idx] would remain null regardless.

C is wrong because while printing null array elements would indeed output null twice, execution never reaches the second loop due to the NPE in the first loop.

Memory tip: Whenever you see an array created with new Type[n] and no explicit initialization, mentally tag every element as null - any method call on those elements is a guaranteed NPE waiting to happen. Also remember: String methods like concat, toUpperCase, and trim return new values; they never mutate in place.

Topics

#Array initialization with nulls#NullPointerException#Method calls on null#Enhanced for loop

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