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Question 1

What primitive types can be written as binary?

Answer 1

byte
short
integer
long

Question 2

Where can’t the underscore in digits be placed?

Answer 2

• At the beginning or end of a number
• Next to a decimal point
• Prior to an F or L suffix
• In positions where an string of digits is expected (for example splitting 0X for hexadecimal in 0_X);

Question 3

Given the following classes:
interface Account{
public default String getId(){ return “0000”; }
}
interface PremiumAccount extends Account{
public String getId();
}

And a class implementing PremiumAccoun, should it implement getId()?

Answer 3

Yes.

getId is redeclared as abstract and should be implemented by the implementing class.

Question 4

Given a try-with-resource construction with two resources. The try throws an Exception and one of the two resources throws an IOException when closed. What will be Exception that is propagated to the method calling?

Answer 4

It will propagate the Exception.

IOException will be added as a suppressed exception to the Exception.

Question 5

Which of the following are reduction methods on the Stream interface?
filter
reduce
sum
max
add

Answer 5

reduce, max

Reduction means going from a Stream of objects to a single object. Filter could still result in multiple results, sum is not available on the Stream interface and add is not a method on the Stream interface.

Question 6

What is the result?

Path p1 = Paths.get(“c:\personal\.\photos\..\readme.txt”); Path p2 = p1.normalize();

Answer 6

c:\personal\readme.txt

. will always be redundant
.. will eliminate the preceding path (photos in this case)

Question 7

Describe the Supplier functional interface

Answer 7

Supplier
R get();

Supplier sup = () -> “test”;

Question 8

Describe the Function functional interface

Answer 8

Function
R apply(T t);

Function fu = (x) -> x.toString();
String y = fu.apply(1);

Question 9

Describe the Predicate functional interface

Answer 9

Predicate
boolean test(T t);

Predicate pre = (x) -> x.equals(“hello”);
Boolean b = pre.test(“hello”);

Question 10

Describe the Consumer functional interface

Answer 10

Consumer
void accept(T t);

Consumer con = (x) -> System.out.println(x);
con.accept(“hello”);

Question 11

Describe the UnaryOperator functional interface

Answer 11

UnaryOperator (extends Function)
T apply(T t);

UnaryOperator op = (x) -> “hello “ + x;
op.apply(“world”);

Question 12

What is the result of the p2, p3 and p4:
Path p1 = Paths.get(“c:\temp\test.txt”);
Path p2 = p1.resolve(Paths.get(“report.pdf”));
Path p3 = p1.resolve(Paths.get(“c:\report.pdf”));
Path p4 = p1.resolve(Paths.get(“”));

Answer 12

p1. c:\temp\test.txt\report.pdf
p2. c:\report.pdf
p3. c:\temp\test.txt

1. If the argument is a relative path (i.e. if it doesn’t start with a root), the argument is simply appended to the path to produce the result.
2. If the argument starts wiith a root it will simply return the argument.
3. If the argument is an empty path it will return this path (p1).

Question 13

What are the rules for the path.relativize(Path path) method?

Answer 13

• If this path and the given path do not have a root component
• If this path and the given path have a root component then the it’s implementation dependent if a path can be constructed
• If this path and the given path are equal, an empty path is returned.

The returned path can be appended to the this path and result in the given path.

Question 14

Given that daylight Savings Time ends on Nov 1 at 2 AM in US/Eastern time zone. (As a result, 2 AM becomes 1 AM.), what will be the result of x?
LocalDateTime ld1 = LocalDateTime.of(2015, Month.NOVEMBER, 1, 2, 0);
ZonedDateTime zd1 = ZonedDateTime.of(ld1, ZoneId.of(“US/Eastern”));
LocalDateTime ld2 = LocalDateTime.of(2015, Month.NOVEMBER, 1, 1, 0);
ZonedDateTime zd2 = ZonedDateTime.of(ld2, ZoneId.of(“US/Eastern”));
long x = ChronoUnit.HOURS.between(zd1, zd2);

Answer 14

-2

Question 15

Given a map with keys of type String and value of type String. When a value exists with key a and value “hello”. How can I merge a value into key a?

Answer 15

map.merge(“a”, “world”, (x, y) -> String::concat);

map.merge takes a BiFunction as the third argument.
When using a class method reference the first argument will be used as the caller for the method, the other arguments are used as parameters for the method reference.

Question 16

True or False

Given a Future object when get is called it will directly return regardless if the Future is completed.

Answer 16

False, get on the Future object will wait untill the future is completed.

Question 17

How can you use Files.find to find all files ending with .java starting in /home, with a directory depth of 5?

Answer 17

Stream s = Files.find(Paths.get(“/home”), 5, (p, a) -> p.endsWith(“.java”));

Note: the stream is lazy.

Question 18

How can you use the Files.lines method to read all lines from a file text.txt?

Answer 18

Stream l = Files.lines(Paths.get(“text.txt”));

Stream l = Files.lines(Paths.get(“text.txt”), Charset.defaultCharset());

Question 19

What is the result of the following?
interface Doer{ 
String doIt(int x, String y); 
}

Doer d = (int a, String b)->b.substring(0, a);

Answer 19

Compiles fine.

It’s not required but it you can state the types in a lambda.

Question 20

What will the following print?
Path p1 = Paths.get(“c:\temp\test1.txt”);
Path p2= Paths.get(“c:\temp\test2.txt”);
Files.copy(p1, p2, StandardCopyOption.COPY_ATTRIBUTES, StandardCopyOption.REPLACE_EXISTING);
if(Files.isSameFile(p1, p2)){
System.out.println(“file copied”);
}else{
System.out.println(“file not copied”);
}

Answer 20

file not copied

Files.isSameFile is meant to check it two paths are the same. It will not check the actual contents of the files.

Question 21

What is the Collectors.summarizing used for?

Answer 21

Takes a ToIntFunction to convert the incoming object to a primitive int. It then returns a IntSummaryStatistics. With for example getSum() methods.

Question 22

What is the result of the following?

Path p1 = Paths.get(“c:\..\temp\test.txt”); System.out.println(p1.normalize().toUri());

Answer 22

file:///c:/temp/test.txt

.. is ignored because the preceding part is the root.

Question 23

How can you truncate a Instant?

Answer 23

Instant now = Instant.now();
now.truncatedTo(ChronoUnit.DAYS);

All fields smaller than DAYS will be set to 0 (hours, minutes, seconds etc.).