1Z0-829 Practice Test 23 — 15 Questions

Question 1

Given:
String[] array = {"A", "B"};
List<String> list = Arrays.asList(array);
list.set(0, "C");
array[1] = "D";
What is the content of the list?

Accepted Answer

[C, D]. `Arrays.asList()` returns a fixed-size list backed by the original array. Modifications to the list via `set()` directly affect the backing array, and modifications to the array elements are reflected in the list. After `list.set(0, "C")`, the first element of both the list and the array becomes "C". After `array[1] = "D"`, the second element of both becomes "D". Thus the list content is [C, D].

Answer

[A, D]

Answer

[A, B]

Answer

[C, B]

Question 2

Which method checks if a String is empty or contains only whitespace?

Accepted Answer

isBlank(). The `isBlank()` method, introduced in Java 11, returns `true` if the string is empty or contains only whitespace characters (as defined by `Character.isWhitespace()`). This makes it the correct and most direct way to check for blank strings, unlike older approaches that require combining multiple checks.

Answer

length() == 0

Answer

isEmpty()

Answer

trim().isEmpty()

Question 3

A financial application uses BigDecimal for monetary calculations. Which rounding mode should be used to round to the nearest neighbor, and if both neighbors are equidistant, round to the even neighbor?

Accepted Answer

RoundingMode.HALF_EVEN. RoundingMode.HALF_EVEN rounds to the nearest neighbor, and when both neighbors are equidistant (i.e., the fractional part is exactly 0.5), it rounds to the even neighbor. This is the standard rounding mode for financial calculations to minimize cumulative rounding bias over many operations.

Answer

RoundingMode.HALF_UP

Answer

RoundingMode.HALF_DOWN

Answer

RoundingMode.UNNECESSARY

Question 4

Which of the following is a checked exception in Java?

Accepted Answer

SQLException. SQLException is a checked exception because it extends Exception directly (not RuntimeException). Checked exceptions must be either caught with a try-catch block or declared in the method signature using 'throws'. SQLException is thrown by JDBC API methods when database access errors occur, forcing the developer to handle potential SQL failures at compile time.

Answer

NullPointerException

Answer

ArrayIndexOutOfBoundsException

Answer

IllegalArgumentException

Question 5

Consider the following code:

```java
boolean a = true, b = false, c = false;
if (a && b || c) {
    System.out.println("True");
} else {
    System.out.println("False");
}
```

What is the output?

Accepted Answer

False. The expression `a && b || c` evaluates as `(a && b) || c` due to operator precedence (`&&` has higher precedence than `||`). With `a=true`, `b=false`, `c=false`, `(true && false)` is `false`, then `false || false` is `false`, so the `else` branch prints "False". Option B is correct.

Answer

The code does not compile because of invalid boolean expression.

Answer

The output cannot be determined without runtime values.

Answer

True

Question 6

A team is migrating a large monolithic Java 8 application to Java 17 using modules. They want to ensure that only the required packages are exported. Which tool should they use to analyze current dependencies and generate module descriptors?

Accepted Answer

jdeps. jdeps is the correct tool because it is specifically designed to analyze class dependencies in Java applications and can generate module descriptor (module-info.java) suggestions. It shows which packages are used and which are not, enabling the team to export only the required packages when migrating to Java modules.

Answer

jlink

Answer

javap

Answer

jar

Question 7

Which class provides a convenient means to read text from a file line by line?

Accepted Answer

BufferedReader. BufferedReader (option D) is the correct answer because it provides the `readLine()` method, which reads text from a character-input stream line by line, efficiently buffering characters to avoid frequent disk reads. When wrapped around a FileReader, it enables convenient and performant line-by-line reading of text files.

Answer

FileReader

Answer

Scanner

Answer

FileInputStream

Question 8

A large-scale data processing platform uses Java to read and write files across multiple nodes. Recently, operations have slowed down significantly. The system uses FileInputStream and FileOutputStream wrapped in BufferedInputStream and BufferedOutputStream with default buffer sizes (8 KB). The operations team suspects that the default buffer size is causing excessive system calls. The files are typically 100 MB to 1 GB in size. Which change would most improve I/O performance while minimizing memory overhead?

Accepted Answer

Increase the buffer size to 64 KB.. Increasing the buffer size to 64 KB reduces the number of system calls (read/write) by allowing more data to be transferred per call. With default 8 KB buffers and 100 MB–1 GB files, the overhead of frequent kernel transitions is significant. A 64 KB buffer strikes a good balance between performance gain and memory overhead, as it is large enough to reduce syscalls substantially without consuming excessive heap space.

Answer

Switch to using FileChannel with direct ByteBuffers for all file operations.

Answer

Use memory-mapped files (MappedByteBuffer) for the entire file.

Answer

Replace FileInputStream with FileReader and FileOutputStream with FileWriter.

Question 9

Given nested loops with labels, which statement correctly breaks out of the outer loop?

Accepted Answer

break outer;. The labeled break statement 'break outer;' terminates the outer loop when executed inside the inner loop. In Java, a label (e.g., 'outer:') placed before a loop allows a break or continue to target that specific loop, overriding the default behavior of breaking only the innermost loop. The other options do not break out of the outer loop: 'continue outer;' would skip the current iteration of the outer loop but not break it, 'return;' would exit the method entirely, and 'break inner;' would break the inner loop but not the outer.

Answer

continue outer;

Answer

return;

Answer

break inner;

Question 10

Given the following code snippet:

```java
outer:
for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        if (i == 1 && j == 1) {
            break outer;
        }
        System.out.print(i + "-" + j + " ");
    }
}
```

What is the output?

Accepted Answer

0-0 0-1 0-2 1-0. The labeled `break outer;` statement exits the outer loop entirely when `i == 1` and `j == 1`. Before that condition is met, the inner loop prints pairs for `i=0` (all j values 0,1,2) and for `i=1` with `j=0`. When `i=1` and `j=1`, the break occurs, so `1-1` is never printed, and the outer loop stops, preventing any further iterations.

Answer

0-0 0-1 0-2 1-0 1-1 1-2

Answer

0-0 0-1 0-2 1-0 2-0 2-1 2-2

Answer

0-0 0-1 0-2 1-0 1-1

Question 11

A team needs to process a large collection of orders to calculate total revenue per region. They decide to use parallel streams to improve performance. Which statement about using parallel streams for this task is true?

Accepted Answer

Using a parallel stream with a stateful lambda operation can lead to incorrect results.. Parallel streams split the workload across multiple threads, and if the lambda operation is stateful (e.g., modifying a shared variable like a counter or a non-thread-safe collection), it can cause race conditions and produce incorrect results. The Streams API documentation explicitly warns against using stateful lambdas with parallel streams to avoid data integrity issues.

Answer

The stream() method returns a parallel stream by default.

Answer

Parallel streams always provide better performance than sequential streams.

Answer

Parallel streams cannot be used with custom thread pools.

Question 12

How many times does the following loop execute? int i=0; while(i<5) { System.out.println(i); i++; }

Accepted Answer

5. The loop starts with i=0, checks the condition i<5 (true), prints i, then increments i. This repeats until i becomes 5, at which point i<5 is false and the loop terminates. Thus, the loop executes exactly 5 times (i=0,1,2,3,4).

Answer

0

Answer

6

Answer

4

Question 13

Given the following switch statement:

```java
int x = 2;
switch (x) {
    default:
        System.out.print("default ");
    case 1:
        System.out.print("1 ");
    case 2:
        System.out.print("2 ");
    case 3:
        System.out.print("3 ");
        break;
    case 4:
        System.out.print("4 ");
}
```

What is the output?

Accepted Answer

2 3. The switch statement starts execution at the matching case (case 2) and then falls through to subsequent cases until a break statement is encountered. Since case 2 has no break, it prints "2 ", then falls through to case 3, prints "3 ", and the break terminates the switch. The default case is not executed because a matching case was found before it.

Answer

2

Answer

2 3 4

Answer

default 1 2 3

Question 14

What is the output of the following code snippet? int x = 5; if(x > 0) { System.out.print('A'); } else if(x > 2) { System.out.print('B'); } else { System.out.print('C'); }

Accepted Answer

A. The condition `x > 0` evaluates to true (x = 5), so the code prints 'A' and then exits the entire if-else-if chain. The subsequent `else if` and `else` blocks are skipped entirely, so only 'A' is output.

Answer

AB

Answer

C

Answer

B

Question 15

What is the output of the following code?
```java
System.out.println(Stream.of(1, 2).map(i -> i * 2.0).count());
```

Accepted Answer

2. The code is:
```java
System.out.println(Stream.of(1, 2).map(i -> i * 2.0).count());
```
This creates a stream of integers 1 and 2, maps each to a Double (2.0 and 4.0), and then calls count() which returns the number of elements in the stream, which is 2. count() returns a long, but when printed, it outputs 2 (not 2.0). Option C is correct because the stream has two elements.

Answer

2.0

Answer

1

Answer

Compilation error