Java OCA OCP Practice Question 3209

Question

Which is the first line in the following code after which the object created in the line marked (0) will be a candidate for garbage collection, assuming no compiler optimizations are done?. 

public class Main {
  static String f() {
    String a = "hello";
    String b = "bye";             // (0)
    String c = b + "!";          // (1)
    String d = b;                 // (2)

    b = a;                        // (3)
    d = a;                        // (4)
    return c;                     // (5)
  }/* w  w  w.j  a v  a  2  s.c o m*/

  public static void main(String[] args) {
    String msg = f();
    System.out.println(msg);     // (6)
  }
}

Select the one correct answer.

  • (a) The line marked (1).
  • (b) The line marked (2).
  • (c) The line marked (3).
  • (d) The line marked (4).
  • (e) The line marked (5).
  • (f) The line marked (6).


(d)

Note

At (1), a new String object is constructed by concatenating the string "bye" in the String object denoted by b and the string "!".

After line (2), d and b are aliases.

After line (3), b and a are aliases, but d still denotes the String object with "bye" from line (0).

After line (4), d and a are aliases.

Reference d no longer denotes the String object created in line (0).

This String object has no references to it and is, therefore, a candidate for garbage collection.




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