Certified Java Programmer Mock Exam

Question 1

class A extends Thread {
  private int i;
  public void run() {i = 1;}
  public static void main(String[] args) {
    A a = new A();
    a.start();
    System.out.print(a.i);
}}

What are the possible results of attempting to compile and run the program?

a.	Prints nothing
b.	Prints: 0
c.	Prints: 1
d.	Prints: 01
e.	Prints: 10
f.	Compile-time error
g.	Run-time error

Question 2

class A extends Thread {
  private int i;
  public void run() {i = 1;}
  public static void main(String[] args) {
    A a = new A();
    a.run();
    System.out.print(a.i);
}}

What is the result of attempting to compile and run the program?

a.	Prints nothing
b.	Prints: 0
c.	Prints: 1
d.	Prints: 01
e.	Prints: 10
f.	Compile-time error
g.	Run-time error
h.	None of the above

Question 3

class A extends Thread {
  public void run() {
    try {sleep(10000);} catch (InterruptedException ie){}
  }
  public static void main(String[] args) {
    A a1 = new A();
    long startTime = System.currentTimeMillis();
    a1.start();
    System.out.print(System.currentTimeMillis() - startTime);
}}

What are the possible results of attempting to compile and run the program?

a.	Prints a number greater than or equal to 0
b.	The number printed must always be greater than 10000
c.	This program will run for at least ten seconds
d.	Compile-time error
e.	Run-time error

Question 4

Which of the following is used to force each thread to reconcile its working copy of a variable with the master copy in main memory?

a.	final
b.	static
c.	synchronized
d.	transient
e.	volatile
f.	native

Question 5

class A extends Thread {
  public void run() {
    synchronized (this) {
      try {wait(5000);} catch (InterruptedException ie){}
  }}
  public static void main(String[] args) {
    A a1 = new A();
    long startTime = System.currentTimeMillis();
    a1.start();
    System.out.print(System.currentTimeMillis() - startTime + ",");
    try {a1.join(6000);} catch (InterruptedException ie) {}
    System.out.print(System.currentTimeMillis() - startTime);
}}

What are the possible results of attempting to compile and run the program?

a.	The first number printed is greater than or equal to 0
b.	The first number printed must always be greater than 5000
c.	The second number printed must always be greater than 5000
d.	The second number printed must always be greater than 6000
e.	The synchronized block inside the run method is not necessary
f.	Compile-time error
g.	Run-time error

Question 6

class A extends Thread {
  String[] sa;
  public A(String[] sa) {this.sa = sa;}
  public void run() {
    synchronized (sa) {
      System.out.print(sa[0] + sa[1] + sa[2]);
}}}
class B {
  private static String[] sa = new String[]{"X","Y","Z"};
  public static void main (String[] args) {
    synchronized (sa) {
      Thread t1 = new A(sa);
      t1.start();
      sa[0] = "A"; sa[1] = "B"; sa[2] = "C";
}}}

What is the result of attempting to compile and run the program?

a.	Prints: XYZ
b.	Prints: AYZ
c.	Prints: ABZ
d.	Prints: ABC
e.	Compile-time error
f.	Run-time error
g.	None of the above

Question 7

class A extends Thread {
  String[] sa;
  public A(String[] sa) {this.sa = sa;}
  public void run() {
    synchronized (sa) {
      while (!sa[0].equals("Done")) {
        try {sa.wait();} catch (InterruptedException ie) {}
    }}
    System.out.print(sa[1] + sa[2] + sa[3]);
}}
class B {
  private static String[] sa = new String[]{"Not Done","X","Y","Z"};
  public static void main (String[] args) {
    Thread t1 = new A(sa);
    t1.start();
    synchronized (sa) {
      sa[0] = "Done";
      sa[1] = "A"; sa[2] = "B"; sa[3] = "C";
      sa.notify();
}}}

What is the result of attempting to compile and run the program?

a.	Prints: XYZ
b.	Prints: AYZ
c.	Prints: ABZ
d.	Prints: ABC
e.	Compile-time error
f.	Run-time error
g.	None of the above

Question 8

Which of the following are true statements?

a.	The Thread.join method is static
b.	The Thread.join method is always invoked on an instance of Thread
c.	The Thread.join method causes the current thread to wait for the referenced thread to die
d.	The Thread.join method declares an InterruptedException in the throws clause
e.	The Thread.join method accepts a timeout value as an argument
f.	The timeout value sets the minimum time that the current thread will wait for the death of the referenced thread
g.	Thread.join will return immediately if the timeout value is zero
h.	A timeout of zero will allow Thread.join to wait forever if necessary

Question 9

Which of the following allows a thread t1 to become the holder of the lock of object obj1.

a.	By blocking on I/O
b.	By entering a synchronized instance method of the obj1
c.	By invoking the wait method on the object
d.	By entering the body of a block that is synchronized on obj1
e.	By entering a synchronized static method of the obj1
f.	By invoking the notify method on obj1

Question 10

After invoking the wait method on an object, obj1, a thread, T1, will remain in the wait set of obj1 until which of the following occurs?

a.	Another thread invokes the notify method on the object, obj1, and T1 is selected to move out of the wait set
b.	Another thread invokes the notifyAll method on the object
c.	Another thread invokes the resume method on thread T1
d.	Another thread interrupts thread T1
e.	The priority of thread T1 is increased
f.	A specified timeout period has elapsed
g.	Another thread invokes the join method on thread T1

Question 11

class A implements Runnable{public void run() {}}
class B {
  public static void main(String[] args) {
    Thread t1 = new Thread();             // 1
    Thread t2 = new Thread(new A());      // 2
    Thread t3 = new Thread(new A(), "A"); // 3
    Thread t4 = new Thread("A");          // 4
}}

A compile-time error is generated at which line?

a.	1
b.	2
c.	3
d.	4
e.	None of the above

Question 12

class A implements Runnable{public void run() {}}
class B {
  public static void main(String[] args) {
    Thread t1 = new Thread();             // 1
    Thread t2 = new Thread(new A());      // 2
    Thread t3 = new Thread("A", new A()); // 3
    Thread t4 = new Thread("A");          // 4
}}

A compile-time error is generated at which line?

a.	1
b.	2
c.	3
d.	4
e.	None of the above

Question 13

class A extends Thread {
  private boolean done;
  public void setDone(boolean done) {this.done = done;}
  public void run() {
    synchronized (this) {
      while (!done) {
        try {wait();} catch (InterruptedException ie){}
  }}}
  public static void main(String[] args) {
    A a1 = new A();
    long startTime = System.currentTimeMillis();
    a1.start();
    System.out.print(System.currentTimeMillis() - startTime);
}}

Which is a possible result of attempting to compile and run the program?

a.	The number printed is greater than or equal to 0
b.	The synchronized block inside the run method is not necessary
c.	This program runs to completion after the elapsed time is printed
d.	Compile-time error
e.	Run-time error
f.	None of the above

Question 14

class A extends Thread {
  public void run() {
    synchronized (this) {
      try {wait();} catch (InterruptedException ie){}
  }}
  public static void main(String[] args) {
    A a1 = new A();
    a1.setDaemon(true);
    long startTime = System.currentTimeMillis();
    a1.start();
    System.out.print(System.currentTimeMillis() - startTime + ",");
}}

Which is a possible result of attempting to compile and run the program?

a.	The number printed is greater than or equal to 0
b.	The synchronized block inside the run method is not necessary
c.	Thread a1 waits forever and the program runs forever
d.	Compile-time error
e.	Run-time error
f.	None of the above

Question 15

class A extends Thread {
  private Object obj;
  public A(Object obj) {this.obj = obj;}
  public void run() {
    try {
      synchronized (obj) {obj.wait();}
    } catch (InterruptedException ie) {}
    System.out.print(Thread.currentThread().getName());
}}
class B {
  private void m1() {
    for (int i = 0; i < 10; i++) {
      A t1 = new A(this);
      t1.setName(String.valueOf(i));
      t1.setDaemon(true);
      t1.start();
    }
    synchronized (this) {notifyAll();}
  }
  public static void main(String[] args) {
    new B().m1();
}}

What are the possible results of attempting to compile and run the program?

a.	All of the numbers 0 through 9 must always be printed
b.	Some or all of the numbers 0 through 9 could be printed
c.	Nothing is printed
d.	Run-time error

Question 16

class C extends Thread {
  private static String[] sa = new String[]{"Not Done","X","Y","Z"};
  public void run() {
    synchronized (sa) {
      while (!sa[0].equals("Done")) {
        try {sa.wait();} catch (InterruptedException ie) {}
    }}
    System.out.print(sa[1] + sa[2] + sa[3]);
  }
  public static void main (String[] args) {
    start();
    synchronized (sa) {
      sa[0] = "Done";
      sa[1] = "A"; sa[2] = "B"; sa[3] = "C";
      sa.notify();
}}}

Which is a possible result of attempting to compile and run the program?

a.	Prints: XYZ
b.	Prints: AYZ
c.	Prints: ABZ
d.	Prints: ABC
e.	Compile-time error
f.	Run-time error
g.	None of the above

Question 17

class C extends Thread {
  private static String[] sa = new String[]{"Not Done","X","Y","Z"};
  public void run() {
    synchronized (this) {
      while (!sa[0].equals("Done")) {
        try {wait();} catch (InterruptedException ie) {}
    }}
    System.out.print(sa[1] + sa[2] + sa[3]);
  }
  void m1() {
      start();
      synchronized (this) {
        sa[0] = "Done";
        sa[1] = "A"; sa[2] = "B"; sa[3] = "C";
  }}
  public static void main (String[] args) {
    new C().m1(); notify();
}}

Which is a possible result of attempting to compile and run the program?

a.	Prints: XYZ
b.	Prints: AYZ
c.	Prints: ABZ
d.	Prints: ABC
e.	Compile-time error
f.	Run-time error
g.	None of the above

Question 18

class A extends Thread {
  public void run() {
    long startTime = System.currentTimeMillis();
    long endTime = startTime + 10000;
    while (System.currentTimeMillis() < endTime) {
      yield();
  }}
  public static void main(String[] args) {
    A a1 = new A();
    long startTime = System.currentTimeMillis();
    a1.start(); sleep(1000); a1.interrupt(); a1.join();
    System.out.print(System.currentTimeMillis() - startTime);
}}

Which is a possible result of attempting to compile and run the program?

a.	Prints a number that is less than 1000
b.	Prints a number between 1000 and 9999
c.	Prints a number larger than 10000
d.	Compile-time error
e.	Run-time error
f.	None of the above

Question 19

class A extends Thread {
  public void run() {System.out.print("A");}
}
class B {
  public static void main (String[] args) {
    A a = new A();
    a.start();
    try {
      a.join();
    } catch (InterruptedException ie) {
      ie.printStackTrace();
    }
    a.start();  // 1
}}

What is the result of attempting to compile and run the program?

a.	The program compiles and runs without error
b.	The second attempt to start thread t1 is successful
c.	The second attempt to start thread t1 is ignored
d.	Compile-time error at marker 1
e.	An IllegalThreadStateException is thrown at run-time
f.	None of the above

Question 20

class A extends Thread {
  private static B b = new B();
  private String s1;
  public void run() {System.out.print(b.m1(s1));}
  A(String threadName, String s1) {
    super(threadName);
    this.s1 = s1;
  }
  public static void main (String[] args) {
    A a = new A("T1","A"), b = new A("T2","B");
    a.start(); b.start();
}}
class B {
  private String s1;
  public synchronized String m1(String s) {
    s1 = s;
    try {Thread.sleep(1);} catch (InterruptedException ie) {}
    return "["+Thread.currentThread().getName()+","+s1+"]";
}}

What are the possible results of attempting to compile and run the program?

a.	Prints nothing
b.	Prints: [T1,A][T2,B]
c.	Prints: [T1,B][T2,B]
d.	Prints: [T2,B][T1,A]
e.	Prints: [T2,A][T1,A]
f.	Compile-time error
g.	Run-time error

Question 21

class A extends Thread {
  static long startTime;
  public void run() {
    for (int i = 0; i < 99999; i++) {Math.sin(i);}
    String name = Thread.currentThread().getName();
    long time = System.currentTimeMillis();
    System.out.println(name + " done at " + (time - startTime));
  }
  public static void main(String[] args) {
    A t1 = new A(); A t2 = new A();
    t1.setName("T1"); t2.setName("T2");
    t1.setPriority(Thread.MIN_PRIORITY);
    t2.setPriority(Thread.MAX_PRIORITY);
    startTime = System.currentTimeMillis();
    t1.start(); t2.start();
}}

Which of the following is a true statement?

a.	The priority assigned to thread T2 is greater than the priority assigned to T1
b.	Java guarantees that thread T2 will get more CPU time than T1
c.	Java guarantess that thread T2 will run to completion before T1
d.	None of the above