SCJP考试中的线程题目分析
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1:
Which two CANNOT dir
ectly cause a thread to stop
executing? (Choose Two)
A.Existing from a synchronized block
B.Calling the wait method on an object
C.Calling notify method on an object
D.Calling read metho
d on an InputStream object
E.Calling the SetPri
ority method on a Thread obj
ect
Answer：AC。同55题
2:
public class SyncTest{
public static void main(String[
] args){
final StringBuffer s1= new Stri
ngBuffer();
final StringBuffer
s2= new StringBuffer();
new Thread () {
public void run() {
synchronized(s1) {
s2.append(“A”);
synchronized(s2) {
s2.append(“B”);
System.out.print(s1);
System.out.print(s2);
}
}
}
}.start();
new Thread() {
public void run() {
synchronized(s2) {
s2.append(“C”);
synchronized(s1) {
s1.append(“D”);
System.out.print(s2);
System.out.print(s1);
}
}
}
}.start();
}
}
Which two statements are true? (
Choose Two)
A. The program prints “ABBCAD”
B. The program prints “CDDACB”
C. The program prints “ADCBADBC”
D. The output is a n
condition
on-deterministic point becau
se of a possible deadlock
E. The output is dep
is running on.
endent on the threading mode
l of the system the program
Answer：DE
3:
What will happen whe
n you attempt to compile and
run the following code?
public class Test{
int i = 0;
public static void main(Strin
g argv[]) {
Test t = new Test();
t.myMethod();
}
public void myMethod(){
while(true) {
try {
wait();
}catch (InterruptedException e
) {}
i++;
}
}
}
A. Compile time erro
r, no matching notify within
the method.
B. Compile and run b
ut an infinite looping of th
e while method.
C. Compilation and run without a
ny output.
E. Runtime Exception
"IllegalMonitorStatExceptio
n".
Answer: E
Note: The wait/notif
synchronized. In this ca
synchronized) and will t
y protocol can only be used
se calling code does not hav
hus cause an Exception at ru
within code that is
e a lock on the object(not
ntime.
4:
1.10 What is the result of compi
ling and executing the following code?
public class ThreadT
est extends Thread {
public void run() {
System.out.println("In run");
yield();
System.out.println("Leaving run");
}
public static void main(String
args []) {
(new ThreadTest()).start();
}
}
A. The code fails to
compile in the main() metho
d.
B. The code fails to
compile in the run() method
.
C. Only the text "In run" will b
e displayed.
D. The text "In run"
followed by "Leaving run" w
ill be displayed.
E. The code compiles correctly,
but nothing is displayed.
Answer: D
5:
1.12 Which of the following will
wait()B. notify()C. yield()D. suspen
definitely stop a thread from executing?A.
d()E. sleep()Answer: ACDE
6:
1.12 Which of the fo
llowing will definitely stop
a thread from executing?
A. wait()
B. notify()
C. yield()
D. suspend()
E. sleep()
Answer: ACDE
7:
Which of the follow
ing statements about threadi
ng are true?
A. You can only obtain a mutuall
extends Thread or implements runnabl
y exclusive lock on methods in a class that
e.
B. You can obtain a mutually exc
lusive lock on any object.
C. You can't obtain
a mutually exclusive lock on
any object.
D. Thread scheduling
algorithms are platform dep
endent.
Answer: BD
8:
Consider the following statement:
Thread myThread = new Thread();
Which of the followi
ng statements are true regar
ding myThread?
A. The thread myThre
ad is now in a runnable stat
e.
B. The thread myThre
ad has a priority of 5.
C. On calling the start() method
class will be executed.
on myThread, the run method in the Thread
D. On calling the st
class will be executed.
art() method on myThread, th
e run method in the calling
Answer: C
Note: the priority o
the constructor.
f myThread will be inherited
from the Thread that called
9:
What is the effect of issuing a
wait() method on an object？（Mutiple）
1) If a notify() met
effect
hod has already been sent to
that object then it has no
2) The object issuing the call t
a notify() or notifyAll() method
o wait() will halt until another object sends
3) An exception will be raised
4) The object issuin
with any other objects u
g the call to wait() will be
sing the receiving object.
automatically synchronized
ANSWER 1)
10:
Pick all the true statements below.
1) If a thread wants
object's lock.
to call wait() on an object
, the thread must own that
2) There is a method that you ca
that puts the instance to sleep for
n call on an instance of the Thread class
a specifiednumber of milliseconds.
3) At the moment whe
the object for which it
n a thread is notified, it a
was waiting.
utomatically gets the lock of
ANSWER 1
11:
1. class Z {
2. public static void main(Str
ing[] args) {
3. new Z();
4. }
5.
6. Z() {
7. Z alias1 = this;
8. Z alias2 = this;
9. synchronized(alias1) {
10. try {
11. alias2.wait();
12. System.out.println("
DONE WAITING");
13. }
14. catch (InterruptedException e) {
15. System.o
ut.println("INTERRUPTED");
16. }
17. catch (Exception e) {
18. System.out.println("
OTHER EXCEPTION");
19. }
20. finally {
21. System.out.println("FINALLY");
22. }
23. }
24. System.out.println("ALL DONE");
25. }
26. }
Mutiple:
1) Compiler error.
2) The application compiles but
doesn't print anything.
3) The application prints "DONE
WAITING".
4) The application prints "INTER
RUPTED".
5) The application prints "OTHER
EXCEPTION".
ANS: 2)
12:
What will happen wh
en you attempt to compile an
d run the following code?
class MyThread extends Thread{
public void run(){
System.out.println
("MyThread: run()");
}
public void start(){////注意，
此方法重写后，不再有CALL RUN（）方法的功能。
System.out.println("MyThread:
start()");
}
}
class MyRunnable implements Runnable{
public void run(){
System.out.println("MyRunnable
: run()");
}
public void start(){//Runnable
否则，将CALL THREAD 的start()执行run
并无此方法，所以，除非本类的对象可以CALL 它，
()
System.out.println
("MyRunnable: start()");
}
}
public class MyTest {
public static void main(String
args[]){
MyThread myThread=new MyThread();
MyRunnable myRunnable = new My
Runnable();
Thread thread=
new Thread(myRunnable);
myThread.start();
thread.start();
}
}
A.prints: MyThread: start() foll
owed by MyRunnable: run()
B.prints: MyThread:
run() followed by MyRunnable
: start()
C.prints: MyThread: start() foll
owed by MyRunnable: start()
D.prints: MyThread: run() follow
ed by MyRunnable: run()
E.compile time error
F.None of the above
ANSWER:A
13:
Multiple objects of
multiple Threads to crea
use the following code?
MyClass (given below) are us
te new integer count. What w
D
ed in a program that uses
ill happen when other threads
class MyClass{
static private int myCount = 0;
int yourNumber;
private static synchronized int
nextCount(){
return ++myCount; //myCount为static
}
public void getYourNumber(){
yourNumber = nextCount();
}
}
A. the code ill give ompilation error
B. the code ill give runtime error
C. each thread will get a unique number
D. the uniqueness of the number
different Threads can’t be guaranteed.
C
14:
What is the effect o
f issuing a wait() method on
an object
Mutiple:
1) If a notify() method has alre
effect
ady been sent to that object then it has no
2) The object issuin
a notify() or notifyAll(
g the call to wait() will ha
) method
lt until another object sends
3) An exception will be raised
4) The object issuing the call t
with any other objects using the rec
o wait() will be automatically synchronized
eiving object.
