804 pretest 解题

Answers with Explanations
1. c)
s1 and s2 not equal
s1 and s3 equal
JVM sets a constant pool in which it stores all the string constants used in the type. If two references are
declared with a constant, then both refer to the same constant object. The == operator checks the similarity of
objects itself (and not the values in it). Here, the first comparison is between two distinct objects, so we get s1
and s2 not equal. On the other hand, since references of s1and s3refer to the same object, we get s1 and
s3 equal.
2. c) [0, 0]
The assignment x = x;inside the construct reassigns the passed parameter; it does notassign the member
xin Point2D. The correct way to perform the assignment is this.x = x;. Field yis not assigned, so its value
remains 0.
3. d) When executed, this program prints
k == j is true
k.equals(j) is true
The Integerobjects are immutable objects. If there is an Integerobject for a value that already exists, then
it does not create a new object again. In other words, Java uses sharing of immutable Integerobjects, so two
Integerobjects are equal if their values are equal (no matter if you use == operators to compare the references or
use equals()method to compare the contents).
4. a) arr1 == arr2 is false
arr1.equals(arr2) is false
Arrays.equals(arr1, arr2) is true
The first comparison between two array objects is carried out using the == operator, which compares object
similarity so it returns false here. The equals()method, which compares this array object with the passed array
object, does not compare values of the array since it is inherited from the Objectclass. Thus we get another false.
On the other hand, the Arraysclass implements various equals()methods to compare two array objects of
different types; hence we get true from the last invocation.
5. d) When executed, this program will print the following: str is not Object.
The variable strwas declared but not instantiated; hence the instanceof operator returns false.
6. b) Side Object Tail Side
Overloading is based on the static type of the objects (while overriding and runtime resolution resolves to the
dynamic type of the objects). Here is how the calls to the overload()method are resolved:
•     overload(firstAttempt);--> firstAttemptis of type Side, hence it resolves to
overload(Side).
•     overload((Object)firstAttempt);-> firstAttemptis casted to Object, hence it resolves to
overload(Object).

•     overload(secondAttempt);-> secondAttemptis of type Tail, hence it resolves to
overload(Tail).
•     overload((Side)secondAttempt);-> secondAttemptis casted to Side, hence it resolves to
overload(Side).
7.  c) foo(long)
For an integer literal, the JVM matches in the following order: int, long, Integer, int.... In other words, it
first looks for an inttype parameter; if it is not provided, then it looks for longtype; and so on. Here, since the int
type parameter is not specified with any overloaded method, it matches with foo(long).
8.  b)
In Base.foo()
In Derived.bar()
A static method is resolved statically. Inside the static method, a virtual method is invoked, which is resolved
dynamically.
9.  d) When executed, the program prints “walk cannot fly”.
In order to override a method, it is not necessary for the overridden method to specify an exception. However, if
the exception is specified, then the specified exception must be the same or a subclass of the specified exception
in the method defined in the super class (or interface).
10.  b) club none none none
Here is the description of matches for the four enumeration values:
“club” matches with the case “Club”. •   
For “Spade”, the case “spade” does not match because of the case difference (switch case  •   
match is case sensitive).
does not match with “diamond” because case statements should exactly match and there are  •   
extra whitespaces in the original string.
“hearts” does not match the string “heart”. •   
11.  a) new Outer.Inner().text
The correct way to access fields of the static inner class is to use the inner class instance along with the outer
class, so new Outer.Inner().textwill do the job.
12.  a) for(Cards card : Cards.values())
System.out.print(card + " ");
The values()method of an enumeration returns the array of enumeration members.
13.  d) class CI12 extends C implements I1, I2 {}
A class inherits another class using the extendskeyword and inherits interfaces using the implementskeyword.
14.  d) interface II extends I1, I2 {}
It is possible for an interface to extend one or more interfaces. In that case, we need to use the extendskeyword
and separate the list of super-interfaces using commas

15.  c) The program will not compile and will result in a compiler error “ambiguous reference to name” in LINE A.
Since nameis defined in both the base interface and the abstractclass, any reference to the member nameis
ambiguous. The first reference to nameis in the line marked with comment LINE A, so the error is flagged in this
line by the compiler.
16.  c) has-a
Composition is a design concept that refers to the has-a relationship.
17.  c) When executed, the program prints the following: Brazil China India Russia.
When nullis passed as a second argument to the Arrays.sort()method, it means that the default Comparable
(i.e., natural ordering for the elements) should be used. The default Comparatorresults in sorting the elements
in ascending order. The program does not result in a NullPointerExceptionor any other exceptions or a
compiler error.
18.  b) When executed, this program prints the following: “The removed element is: 1”.
The remove()method is equivalent to the removeFirst()method, which removes the first element (head of the
queue) of the Dequeobject.
19.  d) When executed, the program prints the following: 1 2.0 3.0.
The List is a generic type that is used here in raw form; hence it allows us to put different types of values in list2.
Therefore, it prints the following: 1 2.0 3.0.
20.  e) When executed, this program will print
SimpleCounter<Double> counter is 2
SimpleCounter<Integer> counter is 2
SimpleCounter counter is 2
Countis a static variable, so it belongs to the classand not to an instance. Each time constructor is invoked,
countis incremented. Since two instances are created, the count value is two.
21.  f ) The program throws an exception for java.util.UnknownFormatConversionException: Conversion = 'l'
There is no format specifier for long int, and the same %dformat specifier for int is used for long as well. So, the
format specifier %ldresults in a runtime exception UnknownFormatConversionException.
22.  b)
Using String.split method: 10 01 2012
Using regex pattern: 10 01 2012
Using str.split(regex)is equivalent to using Pattern.compile(regex).split(str).
23.  d) false true false true
Here are the following regular expression matches for the character x:
•     x*means matches with xfor zero or more times.
•     x+means matches with xfor one or more times.
•     x{n}means match xexactly ntimes.

The pattern a*b+c{3}means match azero or more times, followed by bone or more times, and cexactly
three times.
So, here is the match for elements in the stringsarray:
For  •     "abc", the match fails, resulting in false.
For  •     "abbccc", the match succeeds, resulting in true.
For  •     "aabbcc", the match fails, resulting in false.
For  •     "aaabbbccc", the match succeeds, resulting in true.
24.  d) Severity 1 does not match.
severity3 does not match.
severity five does not match.
Here is the meaning of the patterns used:
[^xyz]   Any character except x, y, or z (i.e., negation)
\s   A whitespace character
[a-z]   from a to z
So the pattern "^severity[\\s+][1–5]"matches the string “severity” followed by whitespace followed by one
of the letters 1 to 5.
For this pattern,
“Severity 1” does not match because of the capital S in “Severity”. •   
“severity 2” matches. •   
“severity3” does not match since there is no whitespace between severity and 3. •   
“severity five” does not match since “five” does not match a numeral from 1 to 5. •   
25.  a) The program prints the following: InvalidKeyException.
It is not necessary to provide an Exceptionthrown by a method when the method is overriding a method defined
with an exception (using the throws clause). Hence, the given program will compile successfully and it will print
InvalidKeyException.
26.  e) The program prints the following: in catch -> in finally ->.
The statement println("after throw -> ");will never be executed since the line marked with the comment
LINE Athrows an exception. The catch handles ArithmeticException, so println("in catch -> ");will be
executed. Following that, there is a return statement, so the function returns. But before the function returns, the
finallystatement should be called, hence the statement println("in finally -> ");will get executed. So,
the statement println("after everything");will never get executed.
27.  f ) Does not print any output on the console
By default, assertions are disabled. If -ea(or the -enableassertionsoption to enable assertions), then
the program would have printed “Error” since the exception thrown in the case of assertion failure is
java.lang.AssertionError, which is derived from the Errorclass.

28.   d) This program will create file1.txt and file3.txt directories in the root directory, and a file2.txt directory in the
“subdir” directory in the root directory.
The mkdirs()method creates a directory for the given name. Since the file names have / in them, the method
creates directories in the root directory (or root path for the Windows drive based on the path in which you
execute this program).
29.   b) When serializing an object that has references to other objects, the serialization mechanism also includes the
referenced objects as part of the serialized bytes.
and
c) When an object is serialized, the class members that are declared as transient will not be serialized (and hence
their values are lost after deserialization).
Option b) and c) are true regarding object serialization.
Option a) is wrong because the Serializableinterface is a marker interface; in other words, the Serializable
interface is an empty interface and it does not declare any methods in it.
Option d) is wrong because the Externalizableinterface declares two methods, writeExternal()and
readExternal().
Option e) is wrong because there is no such exception as NotExternalizableException.
30.  b) Body first head hello program world
TreeSet<String>orders the strings in default alphabetical ascending order and removes duplicates. The
delimiter \W is non-word, so the characters such as < act as separators.
31.  b) beginIndex = 0 and endIndex = 1
In the Pathclass’s method subpath(int beginIndex, int endIndex), beginIndexis the index of the first
element (inclusive of that element) and endIndexis the index of the last element (exclusive of that element). Note
that the name that is closest to the root in the directory hierarchy has index 0. Here, the string element "Program
Files"is the closest to the root C:\, so the value of beginIndexis 0 and endIndexis 1.
32.  d) Prints the following: Copy.class Copy.java Hello.class OddEven.class PhotoCopy.java.
In the Glob pattern “*o*?{java,class,html}”, the character * matches any number of characters, so *o* matches
any string that has “o” in it. The ? matches exactly one character. The pattern {java,class} matches files with the
suffixes of “java” or “class”. Hence, from the given files, the matching file names are Copy.class, Copy.java,
Hello.class, OddEven.class, PhotoCopy.java.
33.  b) WatchService watcher = FileSystems.getDefault().newWatchService();
The getDefault()method in FileSystemsreturns the reference to the underlying FileSystemobject. The
method newWatchService()returns a new watch service that may be used to watch registered objects for
changes and events in files or directories.
34.  The correct options are
c) You can get an instance of PreparedStatementby calling the preparedStatement()method in the Connection
interface.
e) The interface Statementand its derived interfaces implement the AutoCloseableinterface, hence they can be
used with a try-with-resources statement.

Option c) and e) are correct statements. The other three are incorrect for the following reasons:
Option a) Objects of type Statement can handle IN, OUT, and INOUT parameters; you need to  •   
use objects of CallableStatement type for that.
Option b)  •     PreparedStatementis used for pre-compiled SQL statements; the
CallableStatementtype is used for stored procedures.
Option d)  •     CallableStatementimplements the PreparedStatementinterface; PreparedStatement
in turn implements the Statementinterface. These three types are not classes.
35.  e) The program will result in throwing a SQLExceptionbecause auto-commit is true.
If you call methods such as commit()or rollback()when the auto-commit mode is set to true, the program will
a SQLException.
36.  b) RowSetFactory rowSetFactory = RowSetProvider.newFactory();
JdbcRowSet rowSet = rowSetFactory.createJdbcRowSet();
37.  b) When executed, the program prints "Worker"and then the program hangs (i.e., does not terminate).
The statement Thread.currentThread()in the main()method refers to the “Master” thread. Calling the join()
method on itself means that the thread waits itself to complete, which would never happen, so this program
hangs (and does not terminate).
38.  Options a) and d) are true:
a) Takes milliseconds as the argument for time to sleep.
d) Can throw the InterruptedExceptionif it is interrupted by another thread when it sleeps.
In option b), the sleep()method takes milliseconds as an argument, not microseconds.
In option), the sleep()method does not relinquish the lock when it goes to sleep; it holds the lock.
39.  c) The program prints
Starting to wait
Caught Exception
In this program, the wait()method is called without acquiring a lock; hence it will result in throwing an
IllegalMonitorStateException, which will be caught in the catch block for the Exception.
40.  a) The program prints
[10, 5, 10, 20]
[20, 5, 10]
[5, 10, 20]
[5, 10, 20]
Here is the description of the containers that explain the output:
•     Listis unsorted.
•     HashSetis unsorted and retains unique elements.
•     TreeSetis sorted and retains unique elements.
•     ConcurrentSkipListSetis sorted and retains unique elements.

41.  c) The program does not compile and results in a compiler error in the line marked with comment LINE A.
The class CopyOnWriteArrayListdoes not inherit from ArrayList, so an attempt to assign a
CopyOnWriteArrayListto an ArrayListreference will result in a compiler error (the ArrayListsuffix in the class
named CopyOnWriteArrayListcould be misleading as these two classes do not share an is-a relationship).
42.  c) Prints
E Gamma
R Johnson
R Helm
J Vlissides
and then the program terminates.
The producerclass puts an author on the list and then sleeps for some time. In the meantime, the other thread
(consumer) keeps checking whether the list is non-empty or not. If it is non-empty, the consumer thread removes
the item and prints it. Hence, all four author names get printed.
43.  b)
from=von
subject=betreff
In the resource bundle property files, the key values are separated using the = symbol, with each line in the
resource file separated by a newline character.
44.  c) ResourceBundle_en.properties
Java looks for candidate locales for a base bundle named ResourceBundleand locale French (Canada), and
checks for the presence of the following property files:
ResourceBundle_fr_CA.properties
ResourceBundle_fr.properties
Since both of them are not there, Java searches for candidate locales for the base bundle named
ResourceBundleand a default locale (English - United States):
ResourceBundle_en_US.properties
ResourceBundle_en.properties
Java finds that there is a matching resource bundle, ResourceBundle_en.properties. Hence it loads this
resource bundle.
45.  a) System.out.println(new SimpleDateFormat("hh:mm:ss").format(new Date()));
In the format hh:mm:ss, his for the hour in am/pm (with values in 1–12 range), mis for minutes, and sis
for seconds. The class for creating and using custom date or time pattern strings is SimpleDateFormat. The
expression new Date()creates a Dateobject with the current date and time value.