Core Java: Best practices and bytecodes quiz

Quiz
A fun way to learn more!
With contributions from:
• Manjunathan
• Vaibhav
• Ganesh
www.codeops.tech

Question
What query language does Elasticsearch use?
A. SQL
B. Query DSL
C. Query SSL
D. ElasticClient

Answer
What query language does Elasticsearch use?
A. SQL
B. Query DSL
C. Query SSL
D. ElasticClient

Explanation
B. Query DSL - Query DSL is Elasticsearch’s
native Query Domain Specific Language (DSL)

Question
In Elasticsearch, which filter can be used to combine
multiple filters?
A. term
B. range
C. exists
D. bool

Answer
In Elasticsearch, which filter can be used to combine
multiple filters?
A. term
B. range
C. exists
D. bool

Explanation
D. bool, which is used to combine multiple
filters using must/should

Question
In Elasticsearch, "Synonym" is an example of:
A. tokenizer
B. analyzer
C. token filter
D. character filter

Answer
In Elasticsearch, "Synonym" is an example of:
A. tokenizer
B. analyzer
C. token filter
D. character filter

Explanation
C. Token filter
Here is the usage of “synonym” to filter based
on “synonyms” example:

Question
What will be the behavior of running:
java -server -client HelloWorld
A. Error.
B. It will run in the server mode
C. It will run in the client mode
D. Can't guess!

Answer
What will be the behavior of running:
java -server -client HelloWorld
A. Error.
B. It will run in the server mode
C. It will run in the client mode
D. Can't guess!

Question
How are lambda expressions translated by the Java
compiler and executed by the JVM?
A. Lambda expressions are translated to
anonymous classes
B. Compiler translates to “invokedynamic” method
instruction
C. Compiler translates to “invokevirtual” method
instruction
D. Compiler translates to “invokestatic” method
instruction

Answer
How are lambda expressions translated by the Java
compiler and executed by the JVM?
A. Lambda expressions are translated to
anonymous classes
B. Compiler translates to “invokedynamic” method
instruction
C. Compiler translates to “invokevirtual” method
instruction
D. Compiler translates to “invokestatic” method
instruction

Question
Which of the following was NOT introduced in Java
version 8?
A. Lambda functions
B. Streams API
C. invokedynamic method instruction
D. Joda library as date/time API

Answer
Which of the following was NOT introduced in Java
version 8?
A. Lambda functions
B. Streams API
D. Joda library as date/time API

Explanation
Lambda functions, streams API, and Joda library as
date/time API were introduced in Java version 8.
The invokedynamic method instruction was introduced in
Java 7.
[When functional programming support was added in the
form of lambda functions was added in Java 8, the
compiler and JVM were enhanced to use invokedynamic
instruction.]

Question
class Base {}
class DeriOne extends Base {}
class DeriTwo extends Base {}
class ArrayStore {
public static void main(String []args) {
Base [] baseArr = new DeriOne[3];
baseArr[0] = new DeriOne();
baseArr[2] = new DeriTwo();
System.out.println(baseArr.length);
}
}
A. This program prints the following: 3
B. This program prints the following: 2
C. This program throws an ArrayStoreException
D. This program throws an ArrayIndexOutOfBoundsException

Answer
class Base {}
class DeriOne extends Base {}
class DeriTwo extends Base {}
class ArrayStore {
Base [] baseArr = new DeriOne[3];
baseArr[0] = new DeriOne();
baseArr[2] = new DeriTwo();
System.out.println(baseArr.length);
}
}
A. This program prints the following: 3
B. This program prints the following: 2
D. This program throws an ArrayIndexOutOfBoundsException

Explanation
The variable baseArr is of type Base[] , and it points to
an array of type DeriOne.
However, in the statement baseArr[2] = new
DeriTwo(), an object of type DeriTwo is assigned to
the type DeriOne, which does not share a parent-child
inheritance relationship-they only have a common
parent, which is Base. Hence, this assignment results
in an ArrayStoreException.
Discussion: What is the best practice here?

Question
import java.util.*;
class UtilitiesTest {
List<Integer> intList = new LinkedList<>();
List<Double> dblList = new LinkedList<>();
System.out.println(intList.getClass() == dblList.getClass());
}
}
A. It prints: true
B. It prints: false
C. It results in a compiler error
D. It results in a runtime exception

Answer
import java.util.*;
class UtilitiesTest {
List<Integer> intList = new LinkedList<>();
List<Double> dblList = new LinkedList<>();
System.out.println(intList.getClass() == dblList.getClass());
}
}
A. It prints: true
B. It prints: false
C. It results in a compiler error
D. It results in a runtime exception

Explanation
A. It prints: true
Due to type erasure, after compilation both types are
treated as same LinkedList type.
First type: class java.util.LinkedList
Second type: class java.util.LinkedList

Question
Consider the following program:
class AutoCloseableTest {
try (Scanner consoleScanner = new Scanner(System.in)) {
consoleScanner.close(); // CLOSE
consoleScanner.close();
}
}
}
Which one of the following statements is correct?
A. This program terminates normally without throwing any exceptions
B. This program throws an IllegalStateException
C. This program throws an IOException
D. This program throws an AlreadyClosedException
E. This program results in a compiler error in the line marked with the
comment CLOSE

Answer
Consider the following program:
class AutoCloseableTest {
try (Scanner consoleScanner = new Scanner(System.in)) {
consoleScanner.close(); // CLOSE
consoleScanner.close();
}
}
}
Which one of the following statements is correct?
A. This program terminates normally without throwing any exceptions
B. This program throws an IllegalStateException
C. This program throws an IOException
D. This program throws an AlreadyClosedException
E. This program results in a compiler error in the line marked with the
comment CLOSE

Explanation
A . This program terminates normally without throwing any
exceptions.
The try-with-resources statement internally expands to call the
close() method in the finally block. If the resource is explicitly
closed in the try block, then calling close()
again does not have any effect. From the description of the
close() method in the AutoCloseable interface: “Closes this
stream and releases any system resources associated with it. If
the stream is already closed, then invoking this method has no
effect.”

Question
There are two kinds of streams in the java.io package: character streams
(i.e., those deriving from Reader and Writer interfaces) and byte streams (i.e.,
those deriving from InputStream and OutputStream). Which of the following
statements is true regarding the differences between these two kinds of
streams?
A. In character streams, data is handled in terms of bytes; in byte streams, data
is handled in terms of Unicode characters.
B. Character streams are suitable for reading or writing to files such as
executable files, image files, and files in low-level file formats such as .zip,
.class
C. Byte streams are suitable for reading or writing to text-based I/O such as
documents and text, XML, and HTML files.
D. Byte streams are meant for handling binary data that is not human-readable;
character streams are meant for human-readable characters.

Answer
There are two kinds of streams in the java.io package: character streams
(i.e., those deriving from Reader and Writer interfaces) and byte streams (i.e.,
those deriving from InputStream and OutputStream). Which of the following
statements is true regarding the differences between these two kinds of streams?
A. In character streams, data is handled in terms of bytes; in byte streams, data
is handled in terms of Unicode characters.
B. Character streams are suitable for reading or writing to files such as
executable files, image files, and files in low-level file formats such as .zip,
.class
C. Byte streams are suitable for reading or writing to text-based I/O such as
documents and text, XML, and HTML files.
D. Byte streams are meant for handling binary data that is not human-readable;
character streams are meant for human-readable characters.

Explanation
D . Byte streams are meant for handling binary data that is not
human readable; character streams are for human-readable
characters.
In character streams, data is handled in terms of Unicode
characters, whereas in byte streams, data is handled in terms of
bytes. Byte streams are suitable for reading or writing to files such
as executable files, image files, and files in low-level file formats
such as .zip, .class, and .jar. Character streams are suitable for
reading or writing to text-based I/O such as documents and text,
XML, and HTML files.

Question
Which one of the following options is best suited for generating random
numbers in a multi-threaded application?
A. Using java.lang.Math.random()
B. Using java.util.concurrent.ThreadLocalRandom
C. Using java.util.RandomAccess
D. Using java.lang.ThreadLocal<T>

Answer
Which one of the following options is best suited for generating random
numbers in a multi-threaded application?
A. Using java.lang.Math.random()
B. Using java.util.concurrent.ThreadLocalRandom
C. Using java.util.RandomAccess
D. Using java.lang.ThreadLocal<T>

Explanation
b) Using java.util.concurrent.ThreadLocalRandom
java.lang.Math.random() is not efficient for
concurrent programs. Using ThreadLocalRandom
results in less overhead and contention when
compared to using Random objects in concurrent
programs (and hence using this class type is
the best option in this case).
java.util.RandomAccess is unrelated to random
number generation.
ThreadLocal<T> class provides support for creating
thread-local variables.

Question
Consider the following code segment:
while( (ch = inputFile.read()) != VALUE) {
outputFile.write( (char)ch );
}
Assume that inputFile is of type FileReader , and outputFile is of type
FileWriter , and ch is of type int . The method read() returns the character
if successful, or VALUE if the end of the stream has been reached. What is
the correct value of this VALUE checked in the while loop for end-of-stream?
A. -1
B. 0
C. 255
D. Integer.MAX_VALUE
E. Integer.MIN_VALUE

Answer
Consider the following code segment:
while( (ch = inputFile.read()) != VALUE) {
outputFile.write( (char)ch );
}
Assume that inputFile is of type FileReader , and outputFile is of type
FileWriter , and ch is of type int . The method read() returns the character
if successful, or VALUE if the end of the stream has been reached. What is
the correct value of this VALUE checked in the while loop for end-of-stream?
A. -1
B. 0
C. 255
D. Integer.MAX_VALUE
E. Integer.MIN_VALUE

Explanation
A. -1
The read() method returns the value -1 if end-of-
stream (EOS) is reached, which is checked in this while
loop.

Question
Consider the following program and determine the output:
class Test {
public void print(Integer i) {
System.out.println("Integer");
}
public void print(int i) {
System.out.println("int");
}
public void print(long i) {
System.out.println("long");
}
public static void main(String args[]) {
Test test = new Test();
test.print(10);
}
}
A. The program results in a compiler error (“ambiguous overload”)
B. long
C. Integer
D. int

Answer
Consider the following program and determine the output:
class Test {
public void print(Integer i) {
System.out.println("Integer");
}
public void print(int i) {
System.out.println("int");
}
public void print(long i) {
System.out.println("long");
}
public static void main(String args[]) {
Test test = new Test();
test.print(10);
}
}
A. The program results in a compiler error (“ambiguous overload”)
B. long
C. Integer
D. int

Explanation
D. int
If Integer and long types are specified, a literal will
match to int. So, the program prints int .

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Core Java: Best practices and bytecodes quiz

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