OCJP Samples Questions: Java streams

OCP Java SE 8 Exam
Sample Questions
Java Streams
Hari Kiran & S G Ganesh

Question
Choose the correct option based on this code segment:
"abracadabra".chars().distinct()
.peek(ch -> System. out .printf("%c ", ch)). sorted();
A. It prints: “a b c d r”
B. It prints: “a b r c d”
C. It crashes by throwing a java.util.IllegalFormatConversionException
D. This program terminates normally without printing any output in the
console
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Answer
Choose the correct option based on this code segment:
"abracadabra".chars().distinct()
.peek(ch -> System. out .printf("%c ", ch)). sorted();
A. It prints: “a b c d r”
B. It prints: “a b r c d”
C. It crashes by throwing a java.util.IllegalFormatConversionException
D. This program terminates normally without printing any output in
the console

Explanation
D . This program terminates normally without printing
any output in the console
Since there is no terminal operation provided
(such as count , forEach , reduce, or collect ), this
pipeline is not evaluated and hence the peek does not
print any output to the console.

Question
Choose the correct option based on this program:
class Consonants {
private static boolean removeVowels(int c) {
switch(c) {
case 'a': case 'e': case 'i': case 'o': case 'u': return true;
}
return false;
}
public static void main(String []args) {
"avada kedavra".chars().filter(Consonants::removeVowels)
.forEach(ch -> System.out.printf("%c", ch));
}
}
A. This program results in a compiler error
B. This program prints: "aaaeaa"
C. This program prints: "vd kdvr"
D. This program prints: " avada kedavra "
E. This program crashes by throwing a java.util.IllegalFormatConversionException

Answer
class Consonants {
private static boolean removeVowels(int c) {
switch(c) {
case 'a': case 'e': case 'i': case 'o': case 'u': return true;
}
return false;
}
"avada kedavra".chars().filter(Consonants::removeVowels)
.forEach(ch -> System.out.printf("%c", ch));
}
}
A. This program results in a compiler error
B. This program prints: "aaaeaa"
C. This program prints: "vd kdvr"
D. This program prints: " avada kedavra "
E. This program crashes by throwing a java.util.IllegalFormatConversionException

Explanation
B . This program prints: " aaaeaa“
Because the Consonants::removeVowels returns true
when there is a vowel passed, only those characters are
retained in the stream by the filter method.
Hence, this program prints “aaaeaa”.

Question
Choose the best option based on this program:
import java.util.stream.Stream;
public class AllMatch{
boolean result = Stream.of("do", "re", "mi", "fa", "so", "la", "ti")
.filter(str -> str.length() > 5) // #1
.peek(System.out::println) // #2
.allMatch(str -> str.length() > 5); // #3
System.out.println(result);
}
}
A. This program results in a compiler error in line marked with comment #1
B. This program results in a compiler error in line marked with comment #2
C. This program results in a compiler error in line marked with comment #3
D. This program prints: false
E. This program prints the strings “do”, “re”, “mi”, “fa”, “so”, “la”, “ti”, and
“false” in separate lines
F. This program prints: true

Answer
public class AllMatch{
boolean result = Stream.of("do", "re", "mi", "fa", "so", "la", "ti")
.filter(str -> str.length() > 5) // #1
.peek(System.out::println) // #2
.allMatch(str -> str.length() > 5); // #3
System.out.println(result);
}
}
A. This program results in a compiler error in line marked with comment #1
B. This program results in a compiler error in line marked with comment #2
C. This program results in a compiler error in line marked with comment #3
D. This program prints: false
E. This program prints the strings “do”, “re”, “mi”, “fa”, “so”, “la”, “ti”, and
“false” in separate lines
F. This program prints: true

Explanation
F . This program prints: true
The predicate str -> str.length() > 5 returns false for all the
elements because the length of each string is 2.
Hence, the filter() method results in an empty stream and the
peek() method does not print anything. The allMatch()
method returns true for an empty stream and does not
evaluate the given predicate.
Hence this program prints true

Question
import java.util.regex.Pattern;
public class SumUse {
Stream<String> words = Pattern.compile(“ “).splitAsStream(“a bb ccc”);
System.out.println(words.map(word -> word.length()).sum());
}
}
A. Compiler error: Cannot find symbol “sum” in interface Stream<Integer>
B. This program prints: 3
C. This program prints: 5
D. This program prints: 6
E. This program crashes by throwing java.lang.IllegalStateException

Answer
import java.util.regex.Pattern;
public class SumUse {
Stream<String> words = Pattern.compile(“ “).splitAsStream(“a bb ccc”);
System.out.println(words.map(word -> word.length()).sum());
}
}
A. Compiler error: Cannot find symbol “sum” in interface Stream<Integer>
B. This program prints: 3
D. This program prints: 6
E. This program crashes by throwing java.lang.IllegalStateException

Explanation
A . Compiler error: Cannot find symbol “sum” in interface
Stream<Integer>
Data and calculation methods such as sum() and average()
are not available in the Stream<T> interface; they are
available only in the primitive type versions IntStream,
LongStream, and DoubleStream.
To create an IntStream , one solution is to use mapToInt()
method instead of map() method in this program. If
mapToInt() were used, this program would compile without
errors, and when executed, it will print 6 to the console.

Question
Determine the behaviour of this program:
class LambdaFunctionTest {
@FunctionalInterface
interface LambdaFunction {
int apply(int j);
boolean equals(java.lang.Object arg0);
}
LambdaFunction lambdaFunction = i -> i * i; // #1
System.out.println(lambdaFunction.apply(10));
}
}
A. This program results in a compiler error: interfaces cannot be defined inside
classes
B. This program results in a compiler error: @FunctionalInterface used for
LambdaFunction that defines two abstract methods
C. This program results in a compiler error in code marked with #1: syntax error
D. This program compiles without errors, and when run, it prints 100 in console

Answer
Determine the behaviour of this program:
class LambdaFunctionTest {
@FunctionalInterface
interface LambdaFunction {
int apply(int j);
boolean equals(java.lang.Object arg0);
}
LambdaFunction lambdaFunction = i -> i * i; // #1
System.out.println(lambdaFunction.apply(10));
}
}
A. This program results in a compiler error: interfaces cannot be defined inside
classes
B. This program results in a compiler error: @FunctionalInterface used for
LambdaFunction that defines two abstract methods
C. This program results in a compiler error in code marked with #1: syntax error
D. This program compiles without errors, and when run, it prints 100 in
console

Explanation
D. is the correct answer as this program compiles without
errors, and when run, it prints 100 in console.
Why other options are wrong:
A. An interface can be defined inside a class
B. The signature of the equals method matches that of the
equal method in Object class; hence it is not counted as
an abstract method in the functional interface
C. It is acceptable to omit the parameter type when there
is only one parameter and the parameter and return
type are inferred from the LambdaFunction abstract
method declaration int apply(int j)

Question
import java.util.*;
class Sort {
List<String> strings = Arrays.asList("eeny ", "meeny ", "miny ", "mo ");
Collections.sort(strings, (str1, str2) -> str2.compareTo(str1));
strings.forEach(string -> System.out.print(string));
}
}
A. Compiler error: improper lambda function definition
B. This program prints: eeny meeny miny mo
C. This program prints: mo miny meeny eeny
D. This program will compile fine, and when run, will crash by throwing a
runtime exception.

Answer
import java.util.*;
class Sort {
List<String> strings = Arrays.asList("eeny ", "meeny ", "miny ", "mo ");
Collections.sort(strings, (str1, str2) -> str2.compareTo(str1));
strings.forEach(string -> System.out.print(string));
}
}
A. Compiler error: improper lambda function definition
B. This program prints: eeny meeny miny mo
C. This program prints: mo miny meeny eeny
D. This program will compile fine, and when run, will crash by throwing a
runtime exception.

Explanation
C . This program prints: mo miny meeny eeny
This is a proper definition of a lambda expression. Since the
second argument of Collections.sort() method takes the
functional interface Comparator and a matching lambda
expression is passed in this code.
Note that second argument is compared with the
first argument in the lambda expression (str1, str2) ->
str2.compareTo(str1) . For this reason, the comparison is
performed in descending order.

Question
What will be the result of executing this code segment ?
Stream.of("ace ", "jack ", "queen ", "king ", "joker ")
.mapToInt(card -> card.length())
.filter(len -> len > 3)
.peek(System.out::print)
.limit(2);
A. This code segment prints: jack queen king joker
B. This code segment prints: jack queen
C. This code segment prints: king joker
D. This code segment does not print anything on the console

Answer
What will be the result of executing this code segment ?
Stream.of("ace ", "jack ", "queen ", "king ", "joker ")
.mapToInt(card -> card.length())
.filter(len -> len > 3)
.peek(System.out::print)
.limit(2);
A. This code segment prints: jack queen king joker
B. This code segment prints: jack queen
C. This code segment prints: king joker
D. This code segment does not print anything on the console

Explanation
D. This code segment does not print anything on the
console
The limit() method is an intermediate operation and
not a terminal operation.
Since there is no terminal operation in this code
segment, elements are not processed in the stream
and hence it does not print anything on the console.

Question
Choose the correct option based on the following code segment:
Comparator<String> comparer =
(country1, country2) -> country2.compareTo(country2); // COMPARE_TO
String[ ] brics = {"Brazil", "Russia", "India", "China"};
Arrays.sort(brics, null);
Arrays.stream(brics).forEach(country -> System.out.print(country + " "));
A. The program results in a compiler error in the line marked with the comment
COMPARE_TO
B. The program prints the following: Brazil Russia India China
C. The program prints the following: Brazil China India Russia
D. The program prints the following: Russia India China Brazil
E. The program throws the exception InvalidComparatorException

Answer
Choose the correct option based on the following code segment:
Comparator<String> comparer =
(country1, country2) -> country2.compareTo(country2); // COMPARE_TO
String[ ] brics = {"Brazil", "Russia", "India", "China"};
Arrays.sort(brics, null);
Arrays.stream(brics).forEach(country -> System.out.print(country + " "));
A. The program results in a compiler error in the line marked with the comment
COMPARE_TO
B. The program prints the following: Brazil Russia India China
C. The program prints the following: Brazil China India Russia
D. The program prints the following: Russia India China Brazil
E. The program throws the exception InvalidComparatorException

Explanation
C. The program prints the following: Brazil China India
Russia.
For the sort() method, null value is passed as the
second argument, which indicates that the elements’
“natural ordering” should be used. In this case,
natural ordering for Strings results in the strings
sorted in ascending order.
Note that passing null to the sort() method does not
result in a NullPointerException.

Question
public class Reduce {
Stream<String> words = Stream.of("one", "two", "three");
int len = words.mapToInt(String::length).reduce(0, (len1, len2) ->
len1 + len2);
System.out.println(len);
}
}
A. This program does not compile and results in compiler error(s)
B. This program prints: onetwothree
D. This program throws an IllegalArgumentException

Answer
public class Reduce {
Stream<String> words = Stream.of("one", "two", "three");
int len = words.mapToInt(String::length).reduce(0, (len1, len2) ->
len1 + len2);
System.out.println(len);
}
}
A. This program does not compile and results in compiler error(s)
B. This program prints: onetwothree
D. This program throws an IllegalArgumentException

Explanation
This program compiles without any errors. The
variable words point to a stream of Strings. The call
mapToInt(String::length) results in a stream of
Integers with the length of the strings. One of the
overloaded versions of reduce() method takes two
arguments:
T reduce(T identity, BinaryOperator<T> accumulator);
The first argument is the identity value, which is given
as the value 0 here.
The second operand is a BinaryOperator match for the
lambda expression (len1, len2) -> len1 + len2. The
reduce() method thus adds the length of all the three
strings in the stream, which results in the value 11.

Question
Choose the correct option based on this code segment :
List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5);
ints.replaceAll(i -> i * i); // LINE
System.out.println(ints);
A. This code segment prints: [1, 2, 3, 4, 5]
B. This program prints: [1, 4, 9, 16, 25]
C. This code segment throws java.lang.UnsupportedOperationException
D. This code segment results in a compiler error in the line marked with the
comment LINE

Answer
Choose the correct option based on this code segment :
List<Integer> ints = Arrays.asList(1, 2, 3, 4, 5);
ints.replaceAll(i -> i * i); // LINE
System.out.println(ints);
A. This code segment prints: [1, 2, 3, 4, 5]
B. This program prints: [1, 4, 9, 16, 25]
C. This code segment throws java.lang.UnsupportedOperationException
D. This code segment results in a compiler error in the line marked with the
comment LINE

Explanation
b) This program prints: [1, 4, 9, 16, 25]
The replaceAll() method (added in Java 8 to the List
interface) takes an UnaryOperator as the argument. In
this case, the unary operator squares the integer
values. Hence, the program prints [1, 4, 9, 16, 25].

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OCJP Samples Questions: Java streams

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OCJP Samples Questions: Java streams