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Oracle 1z1-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

Question 1

Given:
java
String colors = "red\n" +
"green\n" +
"blue\n";
Which text block can replace the above code?

A. java
String colors = """
red \t
green\t
blue \t
""";
B. java
String colors = """
red \s
green\s
blue \s
""";
C. java
String colors = """
red \
green\
blue \
""";
D. None of the propositions
E. java
String colors = """
red
green
blue
""";

Question 2

Given:
java
var array1 = new String[]{ "foo", "bar", "buz" };
var array2[] = { "foo", "bar", "buz" };
var array3 = new String[3] { "foo", "bar", "buz" };
var array4 = { "foo", "bar", "buz" };
String array5[] = new String[]{ "foo", "bar", "buz" };
Which arrays compile? (Select 2)

A. array1
B. array3
C. array5
D. array2
E. array4

Question 3

Given:
java
Object input = 42;
String result = switch (input) {
case String s -> "It's a string with value: " + s;
case Double d -> "It's a double with value: " + d;
case Integer i -> "It's an integer with value: " + i;
};
System.out.println(result);
What is printed?

A. It's an integer with value: 42
B. It's a string with value: 42
C. Compilation fails.
D. null
E. It throws an exception at runtime.
F. It's a double with value: 42

Question 4

Given:
java
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("A");
list.add("B");
list.add("C");
// Writing in one thread
new Thread(() -> {
list.add("D");
System.out.println("Element added: D");
}).start();
// Reading in another thread
new Thread(() -> {
for (String element : list) {
System.out.println("Read element: " + element);
}
}).start();
What is printed?

A. It prints all elements, but changes made during iteration may not be visible.
B. It prints all elements, including changes made during iteration.
C. Compilation fails.
D. It throws an exception.

Question 5

Given:
java
var sList = new CopyOnWriteArrayList<Customer>();
Which of the following statements is correct?

A. The CopyOnWriteArrayList class is a thread-safe variant of ArrayList where all mutative operations are implemented by making a fresh copy of the underlying array.
B. Element-changing operations on iterators of CopyOnWriteArrayList, such as remove, set, and add, are supported and do not throw UnsupportedOperationException.
C. The CopyOnWriteArrayList class is not thread-safe and does not prevent interference amongconcurrent threads.
D. The CopyOnWriteArrayList class's iterator reflects all additions, removals, or changes to the list since the iterator was created.
E. The CopyOnWriteArrayList class does not allow null elements.

Solutions: