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7 / 10Java-variables and data typesHardJava

Consider the following:

String s = null;
int len = s.length();

What happens at runtime?

  1. Compilation fails

  2. Runtime error: NullPointerException

  3. Runtime error: ClassCastException

  4. Prints 0

  5. Prints 4

Show answer & explanation

Correct answer

Runtime error: NullPointerException

Explanation

Attempting to invoke an instance method on a `null` reference throws a `NullPointerException`. `String` is a reference type, and `s` is `null`, so `s.length()` triggers the exception.

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  6. 6.Which of the following is a valid declaration for a multi-dimensional array of `double` with 3 rows and 4 columns, where all elements are…
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