Elance CORE JAVA Test Answers 2015
·
Which one of the following is NOT a reserved
word in Java?
virtual
public
private
final
Which one of the following statements is true
about Java Beans?
Java Beans are user defined classes.
All Java Beans must extend the java.bean base class
Java Beans cannot be used in server side
programming, they are only used for Graphical User Interfaces.
Java Beans are not permitted to create any threads
What method should you always override when
you have overridden the equals() method?
wait()
toString()
hashCode()
clone()
Which of these are advantages of encapsulation
in Java?
Encapsulation in Java makes unit testing easy
Encapsulation reduces coupling of modules and
increase cohesion inside a module
Encapsulated code is easy to change with new requirements
All of these
The Core Java platform provides many benefits
to developers, including:
Superior speed and performance compared to native
code
Direct compilation to native code on most platforms
A consistent programming interface across multiple
hardware platforms
A purely functional programming language with a
minimalist design philosophy
The Thread.sleep() method:
Causes all threads to suspend execution
Suspends execution in synchronized methods only
Causes the current thread to suspend execution
Causes the hosted virtual machine to suspend all
forms of execution
To document an API, which tool do you use?
javaApi
documentcreate
javadoc
apicreate
To define a child class from the Parent class
following is used:
class Child extends Parent
class Child extends Public Parent
class Child : Parent
class Child :: Parent
If we want a class not to be overridden,the
class must be done as
Class should be abstract
Class should be final
Class should public
Class should be static
Java handles memory allocation and reuse using
a process called:
Virtual Memory
Buddy Blocks
Manual Memory Management
Garbage Collection
Which additional keyword may be used with
try-catch blocks?
finally
finish
finalize
final
The "javac" command line tool is
used to:
Convert java bytecode files into native executables
Compile java source files into bytecode class files
Generate C headers and stubs for native methods
Compress collections of java class files into .jar
archives
The most reliable way to compare two Strings
for equality is by:
Using the == operator on the objects
Using the == operator on the .value() of each
object
Using the &= operator on the objects
Using the .equals() or .compareTo() method of one
object on the other
The part of a "try" block that is
always executed is:
"enum"
"import"
"finally"
"if"
What is an example of proper capitalization
for a class name?
CamelCase
CAMELcase
camELCase
camelcase
What is the correct syntax for importing
java.util.Scanner?
import.java.util.scanner;
import. java.util.Scanner;
import.java.util.scanner.
import java.util.Scanner;
Finally is used to....
ensure a block of code is executed when the JVM
shuts down.
ensure a block of code is executed only when
try/catch completes with an exception
ensure a block of code is executed only when
try/catch completes without an exception
ensure a block of code is always executed after a
try/catch
How can you stop your class from being
inherited by another class?
Declare the class as final.
It’s not possible.
Declare the class default constructor as private.
Declare the class as abstract.
What is the most efficient way to concatenate
a large number of strings in Java?
The StringBuffer object.
The + operator.
Which of the following is a valid constructor
signature?
static className()
public className()
public void className()
public static className()
If a method or variable is marked as having
the "private" access level, then it can only be accessed from:
Inside the same class, or any of its superclasses
Inside the same class
Inside the same class or its parent class
Inside the same class, or a subclass
Can an abstract class be a final class?
Yes
No
What is @Override annotation used for?
It just makes your code easier to read
It makes compiler check that method is really
overridden
It makes method virtual
Interfaces are useful for...
reducing heap size
creating a design contract that encapsulates
implementation
implementing an abstract factory pattern
making an abstract class concrete
What is the correct way to create an instance
of a class?
ClassName varName = new ClassName(arguments);
varName ClassName = new varName(arguments);
ClassName varName = new ClassName(new ClassName);
ClassName varName => new ClassName();
When you create a thread with the “new”
operator – which one of the following statements is true about its state
it is blocked until another thread calls notify()
it will be “runnable” when start() method is called
it is in “runnable” state
it starts running immediately
A java class which extends another class is
usually described with the word:
subclass
dynamic
overloaded
abstract
True of False? The strictfp keyword ensures
that you get the same result on every platform if you perform operations in the
floating point variable.
True
False
Keyword used to access members or methods of
superclass?
this
Super
native
extends
Which of these is true?
An interface implements another interface and class
A class implements an interface but extends a class
A class implements and extends a class
An interrface extends a class but implements
another interface
The "java" command line tool is used
to:
Compress collections of java class files into .jar
archives
Disassemble .class files back into readable source
code
Load and execute java .class files
Compile java source files into bytecode class files
What is auto boxing?
JVM conversion between primitive types and reference
types
Automatic insertion of brackets by an IDE
It doesn’t occur in Java, only in dynamically typed
JVM languages like Groovy
JVM conversion of int to float values
You want subclasses in any package to have
access to members of a superclass. Which is the most restrictive access that
accomplishes this objective?
protected
transient
private
public
What are all the different types of access
modifiers in Java
private, protected, default, public
private, protected, public
protected, default, public
private, default, public
private, public
How should you create a new class that maps
keys to values, using the Java Collections Framework?
Implement both the Iterator and Array interfaces
Extend the AbstractCollection class, thereby
implementing the AbstractCollection interface
Implement the Queue, List, and Array interfaces
Implement the Map interface, possibly by extending
the AbstractMap class
The Object.wait() method:
Resumes from waiting if notifyAll() is invoked for
the object
Causes the current thread to wait
Resumes from waiting if notify() is invoked for the
object
Resumes from waiting if a specified amount of time
has elapsed
How can we use the class or jar files kept on
the network path, within our projects?
Including the path and class /jar file name in the
Classpath
mentioning the file names in the Path
No the network files can not be used directly
mentioning the Class /Jar file names during
compilation only
by directly copying and including in the same
folder as of the project
The "static" keyword marks something
as:
Belonging to a class, rather than a specific
instance
Not being mutable after initialization
No longer able to be subclassed or overloaded
A constant variable whose value cannot be changed
What is the output of the below code ? int a =
0; int b = 0; if (a++ == 1 || b++ == 1) {} System.out.println(a + " "
+ b);
0 0
1 1
1 0
0 1
What will be the output of the program? public
class Foo { public static void main(String[] args) { try { return; } finally {
System.out.println( "Finally" ); } } }
Compilation fails.
Finally
The code runs with no output.
An exception is thrown at runtime.
What is the benefit of
ConcurrentHashMap<K,V>?
Supports locking the entire table in a way that
prevents all access
All operations are thread-safe and retrieval
operations do not entail locking
It maintains a list through all entries to retrieve
data in the order it was inserted.
Allows null to be used a key or value
When the == comparator is used on two objects,
it checks to see if they:
Are instances of the same class
Are references to exactly the same object
Evaluate to the same value
Have the same value according to the .equals()
method of the first object
The instanceof operator can be used to
determine if an object is:
An instance of a class that implements a given
interface
An instance of a subclass of a class
An instance of a class
(All of these)
When creating a user defined class for storing
objects in a HashMap, which method(s) should be overridden?
The hashCode() method
The constructor method
The equal() method
Both the equals() and hashCode() methods
(You don't need override any methods)
JDBC addresses the issue of transactions.
False
True
What is the name of the method used to start a
thread execution?
resume();
start();
run();
init();
Why is it important to override hashCode()
when you override equals()?
It is NOT important to override hashCode() when
overriding equals().
Overriding equals without hashCode breaks the
contract of hashCode().
equals() will throw an exception if hashCode() is
not overridden as well.
An "overloaded" method has what in
common with one (or more) methods on the same class?
The same return type
The same number of parameters, regardless of type
The same name
The same number and types of parameters
Which class/classes is/are thread safe among
these?
String and StringBuffer
StringBuilder
Which one of these lists contains only Java
programming language keywords?
try, virtual, throw, final, volatile, transient
strictfp, constant, super, implements, do
goto, instanceof, native, finally, default, throws
class, if, void, long, int, continue
byte, break, assert, switch, include
Immutable objects are always...
polymorphic
memory efficient
serializable
thread safe
What is a LinkedHashSet?
A hash set with the performance of a linked list.
A superclass of the HashSet object.
A hash set which can easily be converted into a
linked list.
A hash set which preserves the order in which objects
were inserted.
Calling System.gc() when using a modern JVM :
Should be done after deleting several elements from
a collection.
Is especially important when programming for mobile
or memory limited devices.
Does not necessarily force garbage collection to
occur, and is not idiomatic java.
Is the most straightforward and reliable way to
perform memory management in Java.
Directly and immediately disposes of all orphaned
objects on the heap.
In addition to CORBA, Core Java also supports
network services using:
Remote Procedure Calls
IPX / SPX Protocol
Remote Object Access
Remote Method Invocation
Java provides a class for mutable sequences of
characters, called:
String
MutableString
StringBuffer
CharSequence
The List interface has which superinterfaces?
Set
Collection
Both Collection and Iterable
Iterable
A method without an access modifier (i.e.
public, private, protected) is...
static
protected
package-private
public
private
What is the difference between a checked and
unchecked exception?
Checked exceptions must be caught while unchecked
do not need to be caught
Unchecked exceptions must be caught while checked
do not need to be caught
A checked exception extends Throwable and an
unchecked exception does not.
An unchecked exception extends Throwable and a
checked exception does not.
package test; class Test { } ----------------
package test; class SubTest extends Test{ } Is this code compile without error
if the classes are in separate files?
No
Yes
A class may extend:
Only one non-final class
Only one interface
Only one inner class
Many classes through multiple inheritance
What is the output? int[] xxx = {10, 20};
List<String> list = new ArrayList<String>(10);
list.add("01"); list.add("02");
System.out.println(xxx.length + ", " +list.size());
Compile error
10, 2
2, 10
2, 2
1, 2
Which option is true for StringBuffer and
StringBuilder
StringBuffer are thread safe and StringBuilder are
not thread safe
StringBuffer and StringBuilder are thread safe.
Neither StringBuffer nor StringBuilder are thread
safe.
StringBuffer are not thread safe and StringBuilder
are thread safe.
Java's automatic memory management:
Can be overriden using functions like alloc and
dalloc
Uses hardcoded settings inside each Virtual
Machine, which should not be altered
Can be tuned using Virtual Machine settings
Can be configured to operate statically or
dynamically at compile time
After the following code fragment, what is the
value in a? String s; int a; s = "Foolish boy."; a =
s.indexOf("fool");
1
random value
0
-1
4
enum Example { ONE, TWO, THREE } Which
statement is true?
The expressions (ONE == ONE) and ONE.equals(ONE)
are both guaranteed to be true.
The Example values cannot be used in a raw
java.util.HashMap; instead, the programmer must use a java.util.EnumMap.
The Example values can be used in a
java.util.SortedSet, but the set will NOT be sorted because enumerated types do
NOT implement java.lang.Comparable.
The expression (ONE < TWO) is guaranteed to be true
and ONE.compareTo(TWO) is guaranteed to be less than one.
Java variables are passed into methods as:
Pass-by Reference
Pass-by Value
Neither
Java's String class is
Mutable, and can be subclassed
Final, with immutable instances
Final, but creates mutable instances
Immutable, but can be subclassed
Which of the following is true about
overloading vs overriding methods?
Final methods can be overriden, but not overloaded
Overloading happens at compile time, while
overriding happens at runtime
The argument list of overloaded methods must be of
same data type (unlike overridden methods)
Overloading can arbitrarily change the access of a
method, while overriding can only make it more restrictive
How do you convert int[] to a
ArrayList<Integer>?
Casting
In a loop, creating new Integers.
Using the static Arrays.asList method
Using toArrayList()
A class implementing a singleton pattern
has...
no public constructors and static factory method
and a non-static instance variables.
public constructors instead of a static factory
method and a static instance variable.
no public constructors, a public static factory
method, a static instance variable.
no public constructors, a private static factory
method, a static instance variable.
What is a weak reference?
A reference to an object which may have been
garbage collected when the object is asked for.
A reference to an object which is about to be
garbage collected.
A reference to an object that cannot be garbage
collected.
A reference to an object which has been garbage
collected.
Can the "main" method be overloaded
No
Yes
What type should you use for floating point
monetary calculations?
float
BigDecimal
double
byte
Which statement is true?
Any statement that can throw an Error must be
enclosed in a try block.
The Error class is a RuntimeException.
catch(X x) can catch subclasses of X where X is a
subclass of Exception.
Any statement that can throw an Exception must be
enclosed in a try block.
Which of the following is used to see the
details of compilation
javac -verbose TestExample.java
javac -debug TestExample.java
None of these
javac -detail TestExample.java
What is the issue with the following code?
String s = ""; for(int i = 0; i < 1000000; i++) { s +=
Integer.toString(i); }
It will perform very slowly because
Integer.toString() is slow.
It will not compile.
There are no issues with the above code.
It will perform very slowly because strings are
immutable.
Float p = new Float(3.14f); if (p > 3) {
System.out.print("p is bigger than 3. "); } else {
System.out.print("p is not bigger than 3. "); } finally {
System.out.println("Have a nice day."); } What is the result?
p is bigger than 3. Have a nice day.
Compilation fails.
p is bigger than 3.
p is not bigger than 3. Have a nice day.
What will be printed out if you attempt to
compile and run the following code? int i=9; switch (i) { default:
System.out.println("default "); case 0: System.out.println("zero
"); break; case 1: System.out.println("one "); case 2: System.out.println("two
"); }
default
error default clause not defined
default zero
no output displayed
Which of the following statements about static
inner classes is true?
A static inner class requires a static initializer.
A static inner class has no reference to an
instance of the enclosing class.
A static inner class has access to the non-static
members of the outer class.
A static inner class requires an instance of the
enclosing class.
To create a single instance of a class, we can
go with
Final class
Static class
(none of these)
Abstract class
Java source code is compiled into
Source Code
.Exe
Byte Code
.class
.obj
class X implements Runnable { public static
void main(String args[]) { /* Missing code? */ } public void run() {} } Which
of the following line of code is suitable to start a thread ?
Thread t = new Thread(); x.run();
X run = new X(); Thread t = new Thread(run);
t.start();
Thread t = new Thread(X);
Thread t = new Thread(X); t.start();
What's the output of following error ? class A
{ public Number getNumber(){ return 1; } } class B extends A { public int
getNumber(){ return 2; } } public class Main{ public static void main(String
[]args){ A a = new B(); System.out.println(a.getNumber()); } }
Compilation error
2
1
RuntimeError
What is the output of the following program?
import java.lang.reflect.Method; class TestImpl { public void method() {}
public static void main(String[] args) { Method method =
TestImpl.class.getMethod("method", null); System.out.println(method.getName());
} }
Compilation Error
public void test.TestImpl.method()
None of the Above
All of the classes in the Java Collections
Framework:
Have methods to retrieve their data as an Array
Allow elements to be added to the beginning or end
of their internal List
Involve data structures backed by Arrays
Have methods allowing them to be viewed as both
Maps and Lists
Does interrupt() always force all threads to
terminate?
No, if the interruption is not enabled for the
thread, it will not terminate
Yes, the thread gets to a predefined interruption
point and stops
Yes, after interrupt() is called a thread
terminates immediatelly
Given the code: Integer i= new
Integer("1"); if (i.toString() == i.toString())
System.out.println("Equal"); else System.out.println("Not Equal");
None of the above
Prints "Equal"
Compiler error
Prints "Not Equal"
Anonymous inner classes have access to...
Only synchronized collections in the containing
class
Final, local variables in the containing scope
Only variables passed into the constructor, and no
variables in the containing class
Any local variables in the containing scope
What is the output of the below code ? int a =
0; int b = 0; if (a++ == 1 && b++ == 1); System.out.println(a + "
" + b);
0 0
0 1
1 0
1 1
In your program, you need to read a zip file
(myfile.zip) containing several other data files containing basic Java objects.
Which of the following will allow you to construct a InputStream for the task?
new DataInputStream(new
FileInputStream(“myfile.zip”));
new ZipInputStream(new
ObjectInputStream(“myfile.zip”));
new ZipInputStream(new
FileInputStream(“myfile.zip”));
new ObjectInputStream(new ZipInputStream( new
FileInputStream((“myfile.zip”)));
LinkedBlockingQueue is useful for...
implementing a stack
implementing a producer consumer pattern
binary searches of a list of sorted objects
a synchronized linked list
java.util.Collection is:
An abstract class representing a group of objects,
extended by Set and List
An interface of non-destructive methods used by Set
and List classes
An interface for iterable groups of objects
An abstract interface representing a group of
objects, extended by Set and List
Which one of the following statements is true
about threads in Java
the notify() must be called to wake up threads that
have called wait() and notifyAll() must be called to wake up threads that have
called join().
the notify() method can only be called from inside
a synchronized block or from a synchronized method
the notify() method can not be called if your class
extends Thread class, it can only be called if your class implements the
“Runnable” interface
the notify() method informs the Java Virtual
Machine that it has finished executing
A "blank" final variable (defined
without an initial value):
Is illegal, and will cause an error at compile time
Will raise an exception if its value is accessed or
assigned at runtime
Has a Null value, and will raise an exception if
initialized or assigned later
Can be initialized later, but only in a single
location
which statement is True ?
The notify() method causes a thread to immediately
release its locks.
To call wait(), an object must own the lock on the
thread.
The notify() method is defined in class
java.lang.Thread.
The notifyAll() method must be called from a
synchronized context.
The keyword that ensures a field is coherently
accessed by multiple threads is:
"volatile"
"switch"
"synchronized"
"native"
The TreeMap class is Java's implementation of
which data structure?
Linked list
B-tree
Red-Black tree
B+ tree
I would implement a LRU cache using only JDK
classes by...
A LinkedList and binary search over the last
accessed timestamp
A TreeMap and iteration over values that containing
a last accessed timestamp
An ArrayList and binary search over the last accessed
timestamp
A Hashtable and iteration over all values that
contain a last accessed timestamp.
What is the output? public static void
main(String[] args) { int x=10; if(x++ > 9 && x++ == 12){ ++x; }
System.out.println(x); }
13
10
12
11
Which of the following are not a valid
declarations?
float f = 1.2;
float f =1;
float f = 1.2f;
float f = (float)1.2;
You need to keep a list of one million objects
sorted at all times having 100 random inserts and delete per second. Reads from
the list are always done in sorted order. You would:
Use a TreeMap for fast inserts and iterate over the
list in order to re-sort it after each insert.
Use a PriorityQueue to keep the list ordered at all
times.
Use a shell sort after each insert.
Use a HashMap to keep the list ordered at all
times.
Which code fragments correctly create and
initialize a static array of int elements?
static final int a = { 100,200 };
static final int[] a = new int[2]{ 100,200 };
static final int[] a; static void init() { a = new
int[3]; a[0]=100; a[1]=200; }
static final int[] a; static { a=new int[2];
a[0]=100; a[1]=200; }
Which of the following is true about the
Cloneable interface?
Creates an exact copy of the implementing class by
calling its constructor.
It changes the behavior of the protected clone
method to give a field-by-field (reference) copy of the object.
Is just a marker interface that does nothing.
It provides a clone method that must be
implemented.
Livelock describes a situation in which two or
more threads block each other, because:
Their actions are also responses to the actions of
others, such that all are too busy to respond
Each are waiting on the other thread(s) before
acting, such that no thread takes action
A call to Thread.sleep() has suspended the action on
all threads in the VM
They are unable to gain access to shared resources,
and cannot make any progress
You want to listen TCP connections on port
9000. How would you create the socket?
new Socket(9000);
new Socket(“localhost”, 9000);
new ServerSocket(9000);
new ServerSocket(“localhost”, 9000);
Which two are valid constructors for Thread?
1. Thread(Runnable r, String name) 2. Thread() 3. Thread(int priority) 4.
Thread(Runnable r, ThreadGroup g) 5. Thread(Runnable r, int priority)
1 and 3
1 and 4
2 and 5
2 and 4
1 and 2
The TreeMap and LinkedHashMap classes:
Enable iteration of a map's entries based on
natural ordering of keys only.
Enable iteration of a map's entries in a
deterministic order.
Enable iteration of a map's entries based on the
insertion order of elements only.
Enable iteration of a map's entries based either
natural ordering of keys OR natural ordering of values - depending on the
arguments sent to the constructor.
What will be the output of this code? class
Main { static abstract class Base { protected Base() { init(); } abstract void
init(); } static class Child extends Base { private final int value; public
Child() { value = 5; } @Override public void init() {
System.out.println("value = " + value); } } public static void
main(String[] args) { Child c = new Child(); } }
Runtime exception
Compilation error
value = 0
value = 5
public class Test{ public static void
main(String [] arg){ int x=10; if(x++ > 10 && x++ == 12){ ++x; }
System.out.println(x); } } What is the Output of this code?
10
13
12
11
A Guarded Block is a concurrency idiom in
which:
A
block of code will only ever be executed in synchronized mode
All
statements in a block of code are guaranteed to be executed completely, or not
at all
A
condition is polled before the execution of a code block can proceed
A
block of code is protected by an intrinsic lock obtained from a specific Object
or Class
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