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Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
StringBuffer us = new StringBuffer("US");
StringBuffer uk = new StringBuffer("UK");
Stream<StringBuffer> stream = Stream.of(us, uk);
String output = stream.collect(Collectors.joining("-", "=", ""));
System.out.println(output);
What is the given code fragment's output?

A) US=UK
B) =US-UK
C) US-UK
D) -US=UK
E) An exception is thrown.
F) Compilation fails.

2. Given:
java
public class ThisCalls {
public ThisCalls() {
this(true);
}
public ThisCalls(boolean flag) {
this();
}
}
Which statement is correct?

A) It throws an exception at runtime.
B) It does not compile.
C) It compiles.

3. Given:
java
Map<String, Integer> map = Map.of("b", 1, "a", 3, "c", 2);
TreeMap<String, Integer> treeMap = new TreeMap<>(map);
System.out.println(treeMap);
What is the output of the given code fragment?

A) {a=1, b=2, c=3}
B) {b=1, a=3, c=2}
C) {b=1, c=2, a=3}
D) Compilation fails
E) {c=1, b=2, a=3}
F) {a=3, b=1, c=2}
G) {c=2, a=3, b=1}

4. Given:
java
public class Test {
public static void main(String[] args) throws IOException {
Path p1 = Path.of("f1.txt");
Path p2 = Path.of("f2.txt");
Files.move(p1, p2);
Files.delete(p1);
}
}
In which case does the given program throw an exception?

A) File f2.txt exists while file f1.txt doesn't
B) Neither files f1.txt nor f2.txt exist
C) An exception is always thrown
D) File f1.txt exists while file f2.txt doesn't
E) Both files f1.txt and f2.txt exist

5. Given:
java
Optional o1 = Optional.empty();
Optional o2 = Optional.of(1);
Optional o3 = Stream.of(o1, o2)
.filter(Optional::isPresent)
.findAny()
.flatMap(o -> o);
System.out.println(o3.orElse(2));
What is the given code fragment's output?

A) An exception is thrown
B) Compilation fails
C) Optional[1]
D) Optional.empty
E) 0
F) 2
G) 1

Solutions: