SCJP考试中的线程题目分析
1:
Which two CANNOT directly 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 method on an InputStream object
E.Calling the SetPriority method on a Thread object
Answer：AC。同55题
2:
public class SyncTest{
public static void main(String[] args) {
final StringBuffer s1= new StringBuffer();
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 non-deterministic point because of a possible deadlock condition
E. The output is dependent on the threading model of the system the program is running on.
Answer：DE
3:
What will happen when you attempt to compile and run the following code?
public class Test{
int i = 0;
public static void main(String argv[]) {
Test t = new Test();
t.myMethod();
}
public void myMethod(){
while(true) {
try { wait();
}catch (InterruptedException e) {}
i++;
}
}
}
A. Compile time error, no matching notify within the method.
B. Compile and run but an infinite looping of the while method.
C. Compilation and run without any output.
E. Runtime Exception "IllegalMonitorStatException".
Answer: E
Note: The wait/notify protocol can only be used within code that is synchronized. In this case calling code does not have a lock on the object(not synchronized) and will thus cause an Exception at runtime.
4:
1.10 What is the result of compiling and executing the following code?
public class ThreadTest 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() method.
B. The code fails to compile in the run() method.
C. Only the text "In run" will be displayed.
D. The text "In run" followed by "Leaving run" will be displayed.
E. The code compiles correctly, but nothing is displayed.
Answer: D
5:
1.12 Which of the following will definitely stop a thread from executing?A. wait()B. notify()C. yield()D. suspend()E. sleep()Answer: ACDE
6:
1.12 Which of the following will definitely stop a thread from executing?
A. wait()
B. notify()
C. yield()
D. suspend()
E. sleep()
Answer: ACDE
7:
Which of the following statements about threading are true?
A. You can only obtain a mutually exclusive lock on methods in a class that extends Thread or implements runnable.
B. You can obtain a mutually exclusive lock on any object.
C. You can't obtain a mutually exclusive lock on any object.
D. Thread scheduling algorithms are platform dependent.
Answer: BD
8:
Consider the following statement:
Thread myThread = new Thread();
Which of the following statements are true regarding myThread?
A. The thread myThread is now in a runnable state.
B. The thread myThread has a priority of 5.
C. On calling the start() method on myThread, the run method in the Thread class will be executed.
D. On calling the start() method on myThread, the run method in the calling class will be executed.
Answer: C
Note: the priority of myThread will be inherited from the Thread that called the constructor.
9:
What is the effect of issuing a wait() method on an object？（Mutiple）
1) If a notify() method has already been sent to that object then it has no effect
2) The object issuing the call to wait() will halt until another object sends a notify() or notifyAll() method
3) An exception will be raised
4) The object issuing the call to wait() will be automatically synchronized with any other objects using the receiving object.
ANSWER 1)
10:
Pick all the true statements below.
1) If a thread wants to call wait() on an object, the thread must own that object's lock.
2) There is a method that you can call on an instance of the Thread class that puts the instance to sleep for a specified number of milliseconds.
3) At the moment when a thread is notified, it automatically gets the lock of the object for which it was waiting.
ANSWER 1
11:
1. class Z {
2. public static void main(String[] 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.out.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 "INTERRUPTED".
5) The application prints "OTHER EXCEPTION".
ANS: 2)
12:
What will happen when you attempt to compile and 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 并无此方法，所以，除非本类的对象可以CALL 它，否则，将CALL THREAD 的start()执行run()
System.out.println("MyRunnable: start()");
}
}
public class MyTest {
public static void main(String args[]){
MyThread myThread = new MyThread();
MyRunnable myRunnable = new MyRunnable();
Thread thread = new Thread(myRunnable);
myThread.start();
thread.start();
}
}
A.prints: MyThread: start() followed by MyRunnable: run()
B.prints: MyThread: run() followed by MyRunnable: start()
C.prints: MyThread: start() follow
Which two CANNOT directly 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 method on an InputStream object
E.Calling the SetPriority method on a Thread object
Answer：AC。同55题
2:
public class SyncTest{
public static void main(String[] args) {
final StringBuffer s1= new StringBuffer();
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 non-deterministic point because of a possible deadlock condition
E. The output is dependent on the threading model of the system the program is running on.
Answer：DE
3:
What will happen when you attempt to compile and run the following code?
public class Test{
int i = 0;
public static void main(String argv[]) {
Test t = new Test();
t.myMethod();
}
public void myMethod(){
while(true) {
try { wait();
}catch (InterruptedException e) {}
i++;
}
}
}
A. Compile time error, no matching notify within the method.
B. Compile and run but an infinite looping of the while method.
C. Compilation and run without any output.
E. Runtime Exception "IllegalMonitorStatException".
Answer: E
Note: The wait/notify protocol can only be used within code that is synchronized. In this case calling code does not have a lock on the object(not synchronized) and will thus cause an Exception at runtime.
4:
1.10 What is the result of compiling and executing the following code?
public class ThreadTest 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() method.
B. The code fails to compile in the run() method.
C. Only the text "In run" will be displayed.
D. The text "In run" followed by "Leaving run" will be displayed.
E. The code compiles correctly, but nothing is displayed.
Answer: D
5:
1.12 Which of the following will definitely stop a thread from executing?A. wait()B. notify()C. yield()D. suspend()E. sleep()Answer: ACDE
6:
1.12 Which of the following will definitely stop a thread from executing?
A. wait()
B. notify()
C. yield()
D. suspend()
E. sleep()
Answer: ACDE
7:
Which of the following statements about threading are true?
A. You can only obtain a mutually exclusive lock on methods in a class that extends Thread or implements runnable.
B. You can obtain a mutually exclusive lock on any object.
C. You can't obtain a mutually exclusive lock on any object.
D. Thread scheduling algorithms are platform dependent.
Answer: BD
8:
Consider the following statement:
Thread myThread = new Thread();
Which of the following statements are true regarding myThread?
A. The thread myThread is now in a runnable state.
B. The thread myThread has a priority of 5.
C. On calling the start() method on myThread, the run method in the Thread class will be executed.
D. On calling the start() method on myThread, the run method in the calling class will be executed.
Answer: C
Note: the priority of myThread will be inherited from the Thread that called the constructor.
9:
What is the effect of issuing a wait() method on an object？（Mutiple）
1) If a notify() method has already been sent to that object then it has no effect
2) The object issuing the call to wait() will halt until another object sends a notify() or notifyAll() method
3) An exception will be raised
4) The object issuing the call to wait() will be automatically synchronized with any other objects using the receiving object.
ANSWER 1)
10:
Pick all the true statements below.
1) If a thread wants to call wait() on an object, the thread must own that object's lock.
2) There is a method that you can call on an instance of the Thread class that puts the instance to sleep for a specified number of milliseconds.
3) At the moment when a thread is notified, it automatically gets the lock of the object for which it was waiting.
ANSWER 1
11:
1. class Z {
2. public static void main(String[] 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.out.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 "INTERRUPTED".
5) The application prints "OTHER EXCEPTION".
ANS: 2)
12:
What will happen when you attempt to compile and 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 并无此方法，所以，除非本类的对象可以CALL 它，否则，将CALL THREAD 的start()执行run()
System.out.println("MyRunnable: start()");
}
}
public class MyTest {
public static void main(String args[]){
MyThread myThread = new MyThread();
MyRunnable myRunnable = new MyRunnable();
Thread thread = new Thread(myRunnable);
myThread.start();
thread.start();
}
}
A.prints: MyThread: start() followed by MyRunnable: run()
B.prints: MyThread: run() followed by MyRunnable: start()
C.prints: MyThread: start() follow
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