1Z0-829 Practice Test 31 — 15 Questions

Question 1

A method uses an enhanced for loop to iterate over a list of strings and prints each string. The code is:

```java
List<String> list = List.of("A", "B", "C");
for (String s : list) {
    if (s.equals("B")) {
        break;
    }
    System.out.print(s);
}
```

What is the result?

Accepted Answer

A. The enhanced for loop iterates over the list, and when it encounters the string "B", the break statement immediately exits the loop. Therefore, only "A" is printed before the loop terminates. Option C is correct because the output is just "A".

Answer

The code throws a ConcurrentModificationException.

Answer

ABC

Answer

AB

Question 2

Which change fixes the exception?

Accepted Answer

Change line 4 to: for (int i = 0; i < arr.length; i++). Option A is correct because it changes the loop to start at index 0 and continue while i < arr.length, which correctly iterates over all valid indices (0 to arr.length-1). The original code likely used i <= arr.length, causing an ArrayIndexOutOfBoundsException when accessing arr[i] at i = arr.length. By using i < arr.length, the loop stops before reaching the out-of-bounds index.

Answer

Change line 4 to: for (int i = 1; i <= arr.length; i++)

Answer

Change line 4 to: for (int i = 0; i <= arr.length-1; i++)

Answer

Change line 5 to: System.out.println(arr[i-1]);

Question 3

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. Option C is correct because 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 4

Which two statements about the do-while loop are true?

Accepted Answer

The do-while loop can be used with a label.. Option C is correct because Java allows any loop, including the do-while loop, to be labeled. A label is a valid Java identifier followed by a colon placed immediately before the loop statement, enabling break or continue to transfer control to that labeled point. This is explicitly permitted by the Java Language Specification for all iteration statements.

Answer

The condition is evaluated before the body executes.

Answer

The do-while loop cannot have an initialization statement.

Answer

The do-while loop always executes more times than a while loop with the same condition.

Question 5

What is the output of the following code?

```java
int i = 5;
while (i > 0) {
    System.out.print(i + " ");
    i--;
}
```

Accepted Answer

5 4 3 2 1. The while loop runs as long as i > 0. Starting with i = 5, each iteration prints the current value of i followed by a space, then decrements i by 1. The loop stops when i becomes 0, so the output is '5 4 3 2 1 '.

Answer

The code does not compile because i is not declared final.

Answer

5 4 3 2

Answer

4 3 2 1

Question 6

Which three of the following are valid case values in a traditional switch statement (non-pattern)?

Accepted Answer

42. Option A is correct because in a traditional switch statement (non-pattern), the case values must be compile-time constants of types that are compatible with the switch expression. Integer literals like 42 are valid case values, as they are constant expressions of type int, which is one of the allowed types (byte, short, char, int, their wrapper classes, String, and enum types).

Answer

true

Answer

3.14

Question 7

A developer is implementing a method that processes a collection of objects. The objects are instances of various classes that implement a common interface. The developer wants to use a switch expression to perform different actions based on the runtime type of each object. Which approach is correct?

Accepted Answer

Use a switch expression with pattern matching without a default case if all possible types are covered.. Option D is correct because Java 17+ switch expressions with pattern matching allow exhaustive type coverage without a default case when all possible subtypes of the sealed interface or hierarchy are explicitly listed. This ensures compile-time safety and eliminates the need for a default branch, aligning with the principle of exhaustive pattern matching.

Answer

Use a series of if-else statements with instanceof.

Answer

Use a switch expression with pattern matching and a default case.

Answer

Use a traditional switch statement with instanceof checks and casting.

Question 8

Given the following code:

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

What is the output?

Accepted Answer

0-0 0-1 0-2 2-0 2-1 2-2. The correct answer is D because when i equals 1, the continue outer statement skips the entire inner loop for that iteration, so no output is produced for i=1. The outer loop continues with i=2, printing all j values (0,1,2) for i=2, resulting in the output: 0 0 0 1 0 2 2 0 2 1 2 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 1-2 2-0 2-1 2-2

Answer

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

Question 9

Given: outer: for(int i=0; i<3; i++) { for(int j=0; j<3; j++) { if(j==1) continue outer; } } How many times does the innermost loop body execute?

Accepted Answer

3. The outer loop runs with i=0,1,2. For each i, the inner loop starts j=0, executes the body once, then j=1 triggers 'continue outer', which skips the rest of the inner loop and increments i. Thus the inner loop body executes exactly once per outer iteration, for a total of 3 times.

Answer

0

Answer

9

Answer

6

Question 10

Given: int x=0; do { x++; } while(x<5); How many times does the loop body execute?

Accepted Answer

5. The do-while loop executes the body first, then checks the condition. The variable x starts at 0, increments to 1 on the first iteration, and continues incrementing until x becomes 5. When x is 5, the condition x<5 is false, so the loop stops. The body executed for x values 1, 2, 3, 4, and 5 — a total of 5 times.

Answer

4

Answer

6

Answer

0

Question 11

Which TWO correctly describe the behavior of the following code?

```java
int x = 10;
switch (x) {
    case 10: System.out.print("ten ");
    default: System.out.print("default ");
    case 20: System.out.print("twenty ");
}
```

Accepted Answer

The output is 'ten default twenty '.. Option D is correct because in a Java switch statement, once a matching case is found, all subsequent cases (including the default case) are executed in order until a break statement is encountered. Here, case 10 matches, so it prints 'ten ', then falls through to default (prints 'default '), then falls through to case 20 (prints 'twenty '), producing 'ten default twenty '. This is known as fall-through behavior.

Answer

The default case is never executed because a matching case exists.

Answer

The output is 'ten default ' because case 20 is skipped.

Answer

The code does not compile because default must be the last case.

Question 12

Which statement is correct about the following switch expression? String result = switch(day) { case MONDAY, TUESDAY -> "weekday"; case WEDNESDAY -> "midweek"; default -> "other"; };

Accepted Answer

The switch expression must be terminated with a semicolon.. Option B is correct because switch expressions in Java must be terminated with a semicolon, as they produce a value that is assigned to a variable. The given code uses the arrow syntax (->) and assigns the result to a String variable, so a semicolon is required at the end of the entire switch expression.

Answer

The switch expression is not allowed with a colon.

Answer

The default branch is optional.

Answer

The arrow operator requires a yield statement.

Question 13

Given: Object obj = "Hello"; String result = switch(obj) { case String s -> "String of length " + s.length(); case Integer i -> "Integer"; default -> "Unknown"; }; What is result?

Accepted Answer

"String of length 5". The switch expression uses pattern matching with type patterns. The runtime type of obj is String, so the first case matches, binding the value to s and executing the expression "String of length " + s.length(). Since s is "Hello", s.length() returns 5, so result is "String of length 5". Option C is correct.

Answer

"Unknown"

Answer

Compilation error

Answer

"Integer"

Question 14

Given: int i=0; outer: while(i<3) { for(int j=0; j<3; j++) { if(j==1) break outer; } i++; } What is the value of i after the outer loop?

Accepted Answer

0. The correct answer is D (0) because the `break outer` statement immediately terminates the outer `while` loop when `j` equals 1 during the first iteration of the inner `for` loop. Since `i` is incremented only after the inner loop completes, and the inner loop never finishes its first iteration, `i` remains 0.

Answer

1

Answer

2

Answer

3