java程序员认证模拟题及详细分析(4)_java认证

续：Java程序员认证模拟题及详细分析(1) 和(2) (3)
　　 66． Given the following class outline:
　　 class Example{
　　 private int x;
　　 // rest of class body
　　 public static void main(String args[]){
　　 //implementation of main mehtod}
　　 }
　　 Which statement is true?
　　 A. x=2 is a valid assignment in the main() method of class Example.
　　 B. Changing private int x to int x would make x=2 a valid assignment in the main() method of class Example.
　　 C. Changing private int x to public int x would make x=2 a valid assignment in the main() method of class Example.
　　 D. Changing private int x to static int x would make x=2 a valid assignment in 　the main() method of class Example.
　　 E. Changing class Example to public class Example would make x=2 a valid assignment in the main() method of class Example.

　　 67． Which statement is true about an inner class?
　　 A. It must be anonymous
　　 B. It can not implement an interface
　　 C. It is only accessible in the enclosing class
　　 D. It can access any final variables in any enclosing scope.

　　 68． Which statement is true about the grid bag layout manager?
　　 A. The number of rows and columns is fixed when the container is created.
　　 B. The number of rows and columns is fixed when the GridBagLayout object is created.
　　 C. If a component has a fill value of BOTH, then as the container change size, the component is resized.
D. Every component must carry a non-zero weightx and weighty value when it is added to the container
　　 E. If a row has a weighty value that is non-zero, then as the container changes height, the row changes height.

　　 69． Which statement are true about writing a class that is to handle the events issued by a user interface component.
　　 A. Subclassing an adapter is inappropriate in this case.
　　 B. The class should implement some listener interface
　　 C. A class can implement multiple listener interfaces if desired.
　　 D. A subclass of an AWT component cannot listen to its own events.
　　 E. When implements listener interface, a class need only provide those handler methods that it chooses.

　　 70．The argument for a class?s main() method is called args, and the class is invoked as follows.
java Example cat
　　 What would be the effect of trying to access args[0] in the main method?
　　 A. The value produced is cat
　　 B. The value produced is java
　　 C. The value produced is Example
　　 D. An object of type NullPointerException is thrown.
　　 E. An object of type ArrayIndexOutofBoundsException is thrown.
　　 71． Which best describes the requirements of a fully encapsulated class?
　　 A. Mehtods must not be private.
　　 B. Variables must not be public.
　　 C. The class must be marked final
　　 D. Public methods are all marked final.
　　 E. Modification of the objects state is only possible using method calls.

　　 72．Which contains objects without ordering, duplication, or any particular lookup/retrieval mechanism?
　　 A. Map
　　 B. Set
　　 C. List
　　 D. Collection
　　 E. Enumeration

　　 73．What might cause the current thread to stop executing?
　　 A. An interrupted exception is thrown.
　　 B. The thread execute a sleep() call.
　　 C. The thread constructs a new thread
　　 D. A thread of higher priority becomes ready
　　 E. The thread executes a read() call on InputStream

　　 74．Which statements are true about threads?
　　 A. Threads created from the same class all finish together.
　　 B. A thread can be created only by subclassing java.lang.Thread.
　　 C. Invoking the suspend() method stops a thread so that it cannot be restarted.
　　 D. The Java interpreter?s natural exit occurs when no non-daemon threads remain alive.
　　 E. Uncoordinated changes to shared data by multiple threads may result in the data being read, or left, in an inconsistent state.

　　 75．What might form part of a correct inner class declaration or combined declaration and instantiation?
　　 A. private class C
　　 B. new SimpleInterface(){
　　 C. new ComplexInterface(x){
　　 D. private final abstract class(
　　 E. new ComplexClass() implements SimpleInterface
　　 76． Which statements are true about the garbage collection mechanisms?
　　 A. The garbage collection mechanism release memory at pridictable times.
　　 B. A correct program must not depend upon the timing or order of garbage collection
　　 C. Garbage collection ensures that a program will NOT run out of memory during execution
　　 D. The programmer can indicate that a reference through a local variable is no longer going to be used.
　　 E. The programmer has a mechanism that explicitly and immediately frees the memory used by Java objects.

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答案及详细分析：

66．D
main()方法是静态方法，静态方法不能直接访问非静态成员。
67．D
此题考察学生对内部类属性的掌握情况。内部类可以实现接口；匿名类是内部类的一种；内部类通过各种方式可以在包含它的类的外部被访问到；内部类被定义在块中时，只能访问包含它的块的final类型变量。故选择D。
68．C
此题考察考生对类GridBagLayout、及类GridBagConstraints的掌握情况，请考生查阅API文档。
69．B、C
此题考察考生对事件处理的理解。D选项是错的，因为控件可以监听自己的事件。另外，当实现一个接口时，必须实现它内部的所有的方法，所以E选项也是错的。
70．A
命令行参数是紧跟在类名后面的。所以本题中参数由“cat”提供。
71．E
在完全封装类中，一般的定义方式是将所有的成员变量定义为“private”，而将访问这些变量的方法定义为非“private”类型，这样可以在类的外部间接地访问这些变量。所以E选项是最符合这个意思的。
72．B
此题考察“Collection API”的一些知识。实现接口“Set”的类内部所存储的对象是没有顺序，但是允许重复的。另请注意其它几个接口的特征。
73．A、B、D、E
当新线程被创建时，只是使它变为可运行状态而已，并不能使当前线程停止执行。当调用read()方法时，它与输入输出打交道，可能造成线程的暂停执行。
74．D、E
程序的执行完毕是以用户线程（user threads）的结束而标志结束的，与超级线程（daemon threads）无关。所以D选项是对的。E选项说明的是当不同线程对相同数据进行访问时，可能造成数据毁损。
75．A、B
76．B、D
程序的代码是无法对垃圾回收进行精确控制的，程序代码与垃圾回收是相互独立的系统，并不互相影响。答案D告诉我们程序员可以使一个本地变量失去任何意义，例如给本地变量赋值为“null”；