Java SE 8 Programmer II — Question 84

Given the code fragments:
class Caller implements Callable<String> {
String str;
public Caller (String s) {this.str=s;}
public String call()throws Exception { return str.concat ("Caller");}
}
class Runner implements Runnable {
String str;
public Runner (String s) {this.str=s;}
public void run () { System.out.println (str.concat ("Runner"));}
}
and
public static void main (String[] args) throws InterruptedException, ExecutionException {
ExecutorService es = Executors.newFixedThreadPool(2);
Future f1 = es.submit (new Caller ("Call"));
Future f2 = es.submit (new Runner ("Run"));
String str1 = (String) f1.get();
String str2 = (String) f2.get(); //line n1
System.out.println(str1+ ":" + str2);
es.shutdown();
}
What is the result?

Answer options

• A. The program prints: Run Runner Call Caller : null And the program does not terminate.
• B. The program terminates after printing: Run Runner Call Caller : Run
• C. A compilation error occurs at line n1.
• D. An ExecutionException is thrown at run time.

Correct answer: D

Explanation

The correct answer is D because the Future object for the Runner class does not return a value, which leads to an ExecutionException when attempting to call get() on it. Options A and B are incorrect as they misrepresent the program's behavior, and option C is wrong since the code compiles without issues.