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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. How would you create a ConcurrentHashMap configured to allow a maximum of 10 concurrent writer threads and an initial capacity of 42?
Which of the following options meets this requirement?

A) var concurrentHashMap = new ConcurrentHashMap(42);
B) None of the suggestions.
C) var concurrentHashMap = new ConcurrentHashMap();
D) var concurrentHashMap = new ConcurrentHashMap(42, 10);
E) var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);

2. Given:
java
Object myVar = 0;
String print = switch (myVar) {
case int i -> "integer";
case long l -> "long";
case String s -> "string";
default -> "";
};
System.out.println(print);
What is printed?

A) long
B) integer
C) string
D) It throws an exception at runtime.
E) nothing
F) Compilation fails.

3. 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) An exception is thrown.
D) =US-UK
E) US=UK
F) Compilation fails.

4. Given:
java
Runnable task1 = () -> System.out.println("Executing Task-1");
Callable<String> task2 = () -> {
System.out.println("Executing Task-2");
return "Task-2 Finish.";
};
ExecutorService execService = Executors.newCachedThreadPool();
// INSERT CODE HERE
execService.awaitTermination(3, TimeUnit.SECONDS);
execService.shutdownNow();
Which of the following statements, inserted in the code above, printsboth:
"Executing Task-2" and "Executing Task-1"?

A) execService.run(task2);
B) execService.execute(task1);
C) execService.submit(task2);
D) execService.call(task1);
E) execService.run(task1);
F) execService.call(task2);
G) execService.execute(task2);
H) execService.submit(task1);

5. Which of the following methods of java.util.function.Predicate aredefault methods?

A) or(Predicate<? super T> other)
B) isEqual(Object targetRef)
C) not(Predicate<? super T> target)
D) test(T t)
E) negate()
F) and(Predicate<? super T> other)

Solutions: