OCP Java SE 8 Exam - Sample Questions - Java Streams API

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

Ques4on
Choose the correct op4on 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.u=l.IllegalFormatConversionExcep=on
D. This program terminates normally without prin=ng any output in the
console
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Answer
Choose the correct op4on 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.u=l.IllegalFormatConversionExcep=on
D. This program terminates normally without prin4ng any output in
the console

Explana4on
D . This program terminates normally without prin=ng
any output in the console

Since there is no terminal opera=on 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.

Ques4on
Choose the correct op4on 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.u=l.IllegalFormatConversionExcep=on

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.u=l.IllegalFormatConversionExcep=on

Explana4on
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”.

Ques4on
Choose the best op4on 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”, “=”, 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”, “=”, and
“false” in separate lines
F. This program prints: true

Explana4on
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

Ques4on
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.IllegalStateExcep=on

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.IllegalStateExcep=on

Explana4on
A . Compiler error: Cannot ﬁnd symbol “sum” in interface
Stream<Integer>

Data and calcula=on methods such as sum() and average()
are not available in the Stream<T> interface; they are
available only in the primi=ve type versions IntStream,
LongStream, and DoubleStream.

To create an IntStream , one solu=on 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.

Ques4on
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: @Func=onalInterface used for
LambdaFunc=on 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: @Func=onalInterface used for
LambdaFunc=on 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

Explana4on
D. is the correct answer as this program compiles without
errors, and when run, it prints 100 in console.
Why other op4ons 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 func=onal 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 LambdaFunc=on abstract
method declara=on int apply(int j)

Ques4on

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 func=on deﬁni=on
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
run=me excep=on.

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 func=on deﬁni=on
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
run=me excep=on.

Explana4on
C . This program prints: mo miny meeny eeny

This is a proper deﬁni=on of a lambda expression. Since the
second argument of Collec=ons.sort() method takes the
func=onal 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.

Ques4on
What will be the result of execu4ng 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 execu4ng 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

Explana4on
D. This code segment does not print anything on the
console

The limit() method is an intermediate opera=on and
not a terminal opera=on.

Since there is no terminal opera=on in this code
segment, elements are not processed in the stream
and hence it does not print anything on the console.

Ques4on
Choose the correct op4on 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 excep=on InvalidComparatorExcep=on

Answer
Choose the correct op4on 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 excep=on InvalidComparatorExcep=on

Explana4on
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 NullPointerExcep=on.


Ques4on

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 IllegalArgumentExcep=on

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 IllegalArgumentExcep=on

Explana4on

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 iden=ty, BinaryOperator<T> accumulator);
The ﬁrst argument is the iden=ty 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.

Ques4on
Choose the correct op4on 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.UnsupportedOpera=onExcep=on
D. This code segment results in a compiler error in the line marked with the
comment LINE

Answer
Choose the correct op4on 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.UnsupportedOpera=onExcep=on
D. This code segment results in a compiler error in the line marked with the
comment LINE

Explana4on
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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OCP Java SE 8 Exam - Sample Questions - Java Streams API

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