OCJP Study 15

OCJP(Java 6) 기출문제 연습 15(141~150)

PC나 스마트폰에서도 동일하게 실행되므로 장소를 가리지 않고 OCJP(JAVA 6) 국제 자격증을 목표로 학습할 수 있다.

QUESTION 141
Click the Exhibit button.
1. public class Threads1 {
2. int x = 0;
3. public class Runner implements Runnable {
4. public void run(){
5. int current = 0;
6. for(int i = 0; i<4; i++){
7. current = x;
8. System.out.println(current + ", ");
9. x = current + 2;
10. }
11. }
12. }
13.
14. public static void main(String[] args) {
15. new Threads1().go();
16. }
17.
18. public void go(){
19. Runnable r1 = new Runner();
20. new Thread(r1).start();
21. new Thread(r1).start();
22. }
23.}
Which two are possible results? (Choose two.)

A. 0, 2, 4, 4, 6, 8, 10, 6,
B. 0, 2, 4, 6, 8, 10, 2, 4,
C. 0, 2, 4, 6, 8, 10, 12, 14,
D. 0, 0, 2, 2, 4, 4, 6, 6, 8, 8, 10, 10, 12, 12, 14, 14,
E. 0, 2, 4, 6, 8, 10, 12, 14, 0, 2, 4, 6, 8, 10, 12, 14,

C

the first thread prints 0, 2, 4, 6.
the second thread executes right after the first one and prints 8, 10, 12, 14
ZZZ

QUESTION 142
Given:
foo and bar are public references available to many other threads. foo refers to a Thread and bar is an Object.
The thread foo is currently executing bar.wait(). From another thread, what provides the most reliable way to ensure that foo will stop executing wait()?

A. foo.notify();
B. bar.notify();
C. foo.notifyAll();
D. Thread.notify();
E. bar.notifyAll();
F. Object.notify();

E

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QUESTION 143
Given:
public class PingPong implements Runnable {
synchronized void hit(long n) {
for (int i = 1; i < 3; i++)
System.out.print(n + "-" + i + " ");
}
public static void main(String[] args) {
new Thread(new PingPong()).start();
new Thread(new PingPong()).start();
}
public void run() {
hit(Thread.currentThread().getId());
}
}
Which two statements are true? (Choose two.)

A. The output could be 8-1 7-2 8-2 7-1
B. The output could be 7-1 7-2 8-1 6-1
C. The output could be 8-1 7-1 7-2 8-2
D. The output could be 8-1 8-2 7-1 7-2

C,D

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QUESTION 144
Click the Exhibit button.
class Computation extends Thread {
private int num;
private boolean isComplete;
private int result;
public Computation(int num){ this.num = num; }
public synchronized void run() {
result = num * 2;
isComplete = true;
notify();
}
public synchronized int getResult() {
while ( ! isComplete ){
try {
wait();
} catch (InterruptedException e) {
}
}
return result;
}
public static void main(String[] args) {
Computation[] computations = new Computation[4];
for (int i = 0; i < computations.length; i++) {
computations[i] = new Computation(i);
computations[i].start();
}
for (Computation c : computations) {
System.out.println(c.getResult() + " ");
}
}
}
What is the result?

A. The code will deadlock.
B. The code may run with no output.
C. An exception is thrown at runtime.
D. The code may run with output "0 6".
E. The code may run with output "2 0 6 4".
F. The code may run with output "0 2 4 6".

F

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QUESTION 145
Given:
1. class Mammal {
2. }
3.
4. class Raccoon extends Mammal {
5. Mammal m = new Mammal();
6. }
7.
8. class BabyRaccoon extends Mammal {
9. }
10.
Which four statements are true? (Choose four.)

A. Raccoon is-a Mammal.
B. Raccoon has-a Mammal.
C. BabyRaccoon is-a Mammal.
D. BabyRaccoon is-a Raccoon.
E. BabyRaccoon has-a Mammal.
F. BabyRaccoon is-a BabyRaccoon.

A,B,C,F

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QUESTION 146
Which two code fragments will execute the method doStuff() in a separate thread? (Choose two.)

A. new Thread() {
public void run() { doStuff(); }
};
B. new Thread() {
public void start() { doStuff(); }
};
C. new Thread() {
public void start() { doStuff(); }
}.run();
D. new Thread() {
public void run() { doStuff(); }
}.start();
E. new Thread(new Runnable() {
public void run() { doStuff(); }
}).run();
F. new Thread(new Runnable() {
public void

D,F

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QUESTION 147
Given:
public class Person {
private String name;
public Person(String name) {
this.name = name;
}
public boolean equals(Object o) {
if ( ! ( o instanceof Person) ) return false;
Person p = (Person) o;
return p.name.equals(this.name);
}
}
Which statement is true?

A. Compilation fails because the hashCode method is not overridden.
B. A HashSet could contain multiple Person objects with the same name.
C. All Person objects will have the same hash code because the hashCode method is not overridden.
D. If a HashSet contains more than one Person object with name="Fred", then removing another Person, also with name="Fred", will remove them all.

B

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QUESTION 148
Given:
import java.util.*;
public class SortOf {
public static void main(String[] args) {
ArrayList<integer> a = new ArrayList<integer>();
a.add(1); a.add(5); a.add(3);
Collections.sort(a);
a.add(2);
Collections.reverse(a);
System.out.println(a);
}
}
What is the result?

A. [1, 2, 3, 5]
B. [2, 1, 3, 5]
C. [2, 5, 3, 1]
D. [5, 3, 2, 1]
E. [1, 3, 5, 2]
F. Compilation fails.
G. An exception is thrown at runtime.

C

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QUESTION 149
Given:
public class Person {
private name;
public Person(String name) {
this.name = name;
}
public int hashCode() {
return 420;
}
}
Which statement is true?

A. The time to find the value from HashMap with a Person key depends on the size of the map.
B. Deleting a Person key from a HashMap will delete all map entries for all keys of type Person.
C. Inserting a second Person object into a HashSet will cause the first Person object to be removed as a duplicate.
D. The time to determine whether a Person object is contained in a HashSet is constant and does NOT depend on the size of the map.

A

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QUESTION 150
Given:
import java.util.TreeSet;
public class Explorer2 {
public static void main(String[] args) {
TreeSet < Integer > s = new TreeSet<Integer>();
TreeSet<Integer> subs = new TreeSet<Integer>();
for(int i = 606; i < 613; i++)
if(i%2 == 0) s.add(i);
subs = (TreeSet)s.subSet(608, true, 611, true);
s.add(629);
System.out.println(s + " " + subs);
}
}
What is the result?

A. Compilation fails.
B. An exception is thrown at runtime.
C. [608, 610, 612, 629] [608, 610]
D. [608, 610, 612, 629] [608, 610, 629]
E. [606, 608, 610, 612, 629] [608, 610]
F. [606, 608, 610, 612, 629] [608, 610, 629]

E

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