Java认证考试
Given the following code， which statements concerning the objects referenced through the member variables i， j and k are true， given that any thread may call the methods a， b and c at any time？ （） class Counter { int v = 0； synchronized void inc（） {
题目
Given the following code， which statements concerning the objects referenced through the member variables i， j and k are true， given that any thread may call the methods a， b and c at any time？ （） class Counter { int v = 0； synchronized void inc（） { v++； } synchronized void dec（） { v--； } } public class Q7ed5 { Counter i； Counter j； Counter k； public synchronized void a（） { i.inc（）； System.out.println（"a"）； i.dec（）； } public synchronized void b（） { i.inc（）； j.inc（）； k.inc（）； System.out.println（"b"）； i.dec（）； j.dec（）； k.dec（）； } public void c（） { k.inc（）； System.out.println（"c"）； k.dec（）； } }
- A、i.v is guaranteed always to be 0 or 1.
- B、j.v is guaranteed always to be 0 or 1.
- C、k.v is guaranteed always to be 0 or 1
- D、j.v will always be greater than or equal to k.v at any give time.
- E、k.v will always be greater than or equal to j.v at any give time.
相似问题和答案
第1题：
Which statements concerning the following code are true？（） class a { public a（） {} public a（int i） { this（）； } } class b extends a { public boolean b（String msg） { return false； } } class c extends b { private c（） { super（）； } public c（String msg） { this（）； } public c（int i） {} }
- A、The code will fail to compile.
- B、The constructor in a that takes an int as an argument will never be called as a result of constructing an object of class b or c.
- C、Class c has three constructors.
- D、Objects of class b cannot be constructed.
- E、At most one of the constructors of each class is called as a result of constructing an object of class c.
正确答案:B,C
第2题：
void waitForSignal（） { Object obj = new Object（）； synchronized （Thread.currentThread（）） { obj.wait（）； obj.notify（）； } } Which is true？（）
- A、 This code may throw an InterruptedException.
- B、 This code may throw an IllegalStateException.
- C、 This code may throw a TimeoutException after ten minutes.
- D、 This code will not compile unless “obj.wait（）” is replaced with “（（Thread） obj）.wait（）”.
- E、 Reversing the order of obj.wait（） and obj.notify（） may cause this method to complete normally.
- F、 A call to notify（） or notifyAll（） from another thread may cause this method to complete normally.
正确答案:B
第3题：
A.A finalizer may NOT be invoked explicitly.
B.The finalize method declared in class Object takes no action.
C.super.finalize（）is called implicitly by any over riding finalize method.
D.The finalize method for a given objec twill be called no more than once by the garbage collector.
E.The order in which finalize will be called on two objects is based on the order in which the two objects became finalizable.
第4题：
Given the following class， which statements can be inserted at position 1 without causing the code to fail compilation？（） public class Q6db8 { int a； int b = 0； static int c； public void m（） { int d； int e = 0； // Position 1 } }
- A、a++；
- B、b++；
- C、c++；
- D、d++；
- E、e++；
正确答案:A,B,C,E
第5题：
Given that Thing is a class， how many objects and reference variables are created by the following code？（） Thing item， stuff； item = new Thing（）； Thing entity = new Thing（）；
- A、One object is created
- B、Two objects are created
- C、Three objects are created
- D、One reference variable is created
- E、Two reference variables are created
- F、Three reference variables are created.
正确答案:B,F
第6题：
public class SyncTest { private int x； private int y； private synchronized void setX（ int i ） { x = i； } private synchronized void setY（ int i ） { y = i； } public void setXY（ int i ） { setX（i）； setY（i）； } public synchronized boolean check（） { return x != y； } } Under which condition will check return true when called from a different class？ （）
- A、 check can never return true.
- B、 check can return true when setXY is called by multiple threads.
- C、 check can return true when multiple threads call setX and setY separately.
- D、 check can return true only if SyncTest is changed to allow x and y to be set separately.
正确答案:B
第7题：
public class SyncTest （ private int x； private int y； private synchronized void setX （int i） （x=1；） private synchronized void setY （int i） （y=1；） public void setXY（int 1）（set X（i）； setY（i）；） public synchronized Boolean check（） （return x !=y；） ） Under which conditions will check （） return true when called from a different class？
- A、 Check（） can never return true.
- B、 Check（） can return true when setXY is called by multiple threads.
- C、 Check（） can return true when multiple threads call setX and setY separately.
- D、 Check（） can only return true if SyncTest is changed to allow x and y to be setseparately.
正确答案:B
第8题：
A.int foo() { /* more code here */ }
B.void foo() { /* more code here */ }
C.public void foo() { /* more code here */ }
D.private void foo() { /* more code here */ }
E.protected void foo() { /* more code here */ }
第9题：
Which statements concerning the methods notify（） and notifyAll（） are true？
- A、Instances of class Thread have a method called notify（）.
- B、A call to the method notify（） will wake the thread that currently owns the monitor of the object.
- C、The method notify（） is synchronized.
- D、The method notifyAll（） is defined in class Thread.
- E、When there is more than one thread waiting to obtain the monitor of an object， there is no way to be sure which thread will be notified by the notify（） method.
正确答案:A,E
第10题：
Which of the following commands should be used to show the percentage of time that any given disk was busy？（）
- A、 ps
- B、 tprof
- C、 iostat
- D、 vmstat
正确答案:C