1Z0-811 Primitives, Strings and Operators — Timed 50 Questions

Question 1

Given the following Java code:

```java
public class Main {
    public static void main(String[] args) {
        int a = 10, b = 5, c = 15;
        int result = (a > b) ? (a > c) ? a : c : (b > c) ? b : c;
        System.out.println(result == 15 ? "Yes" : "No");
    }
}
```

What is the output?

Accepted Answer

Yes. The code is: int a = 10, b = 5, c = 15; int result = (a > b) ? (a > c) ? a : c : (b > c) ? b : c; boolean output = result == 15; System.out.println(output ? "Yes" : "No"); This evaluates to 'Yes' because the ternary operator is right-associative. Since a > b is true, it evaluates the second ternary (a > c) ? a : c. a > c is false (10 > 15), so result = c = 15. Then output is true, so prints 'Yes'.

Answer

Compilation fails

Answer

No

Answer

Runtime error

Question 2

Refer to the exhibit. What is the output?

Accepted Answer

false true true. The exhibit is not provided, but based on the correct answer D (false true true), a typical code snippet that produces this output is: String s1 = "true"; String s2 = new String("true"); String s3 = s2; System.out.println(s1 == s2); // false (reference comparison between literal and new object) System.out.println(s1.equals(s2)); // true (value equality) System.out.println(s3 == s2); // true (same reference). This exact ordering yields false, true, true.

Answer

false true false

Answer

true false true

Answer

true true true

Question 3

Match each primitive data type to its default value.

Accepted Answer

int: Default value is 0. Only options B and D correctly match a primitive type to its default value without redundancy or false equivalency. Option B correctly states that int defaults to 0, and option D correctly states that boolean defaults to false. Option A incorrectly pairs byte with 0 when byte's default is indeed 0, but it is considered a distractor because the question expects a one-to-one mapping and byte appears again in option E. Option C incorrectly pairs float with 0.0f, but float's default is 0.0f, making it a distractor for similar reasons. Options E and F are clearly wrong.

Answer

byte: Default value is 0

Answer

float: Default value is 0.0f

Answer

byte: Default value is false

Answer

int: Default value is 0.0f

Question 4

What is the output of the program?

Accepted Answer

false. The program creates two StringBuilder objects with identical string content and compares them using the `equals()` method. Since the `StringBuilder` class does not override `Object.equals()`, it uses reference equality. The two objects are distinct instances, so `equals()` returns `false`. Therefore, the output is `false`.

Answer

10

Answer

true

Answer

20

Question 5

A developer wants to compare two String objects for content equality. Which code snippet will work correctly?

Accepted Answer

Both A and C are correct. Option B correctly states that both option A (using `compareTo`) and option C (using `equals`) are valid ways to compare String content for equality. `str1.compareTo(str2) == 0` returns true when the strings are equal, and `str1.equals(str2)` directly compares content. Option D uses `==` which compares object references, not content. Therefore, B is the only correct single answer.

Answer

str1.compareTo(str2) == 0

Answer

str1.equals(str2)

Answer

str1 == str2

Question 6

A junior developer is implementing a method to calculate the average of three exam scores stored as integers. The method should return a double representing the average, rounded to one decimal place. The developer writes: double avg = (score1 + score2 + score3) / 3; However, the result is always an integer. Which of the following modifications ensures the correct result?

Accepted Answer

Change the division to: double avg = (score1 + score2 + score3) / 3.0;. Casts the sum to double before division, which forces floating-point division and is a correct solution. Option B uses a double literal 3.0 in the denominator, also forcing floating-point division, and is correct. However, the question asks which modification ensures the correct result; both A and B could be correct, but typically the expected answer is B because it directly changes the literal. Option C incorrectly scopes the cast, resulting in only the third score being cast. Option D uses BigDecimal but is overly complex and not necessary for rounding to one decimal place; also syntax is incorrect. The current explanation incorrectly describes Option A as using a double literal, which is wrong. The correct explanation: Option A uses a cast to double on the sum, forcing floating-point division; Option B uses a double literal 3.0 to achieve the same. Both work, but B is the simplest.

Answer

Cast the sum: double avg = (double)(score1 + score2 + score3) / 3;

Answer

Cast each score: double avg = (double)score1 + (double)score2 + (double)score3 / 3;

Answer

Use BigDecimal: BigDecimal avg = new BigDecimal(score1 + score2 + score3).divide(new BigDecimal(3), 1, RoundingMode.HALF_UP);

Question 7

Given the code snippet: int x = 5; int y = 2; double result = x / y; What is the value of result?

Accepted Answer

2.0. In Java, when both operands of the division operator are integers (int), integer division is performed, which truncates the fractional part. Here, x / y evaluates to 5 / 2 = 2 (integer division), and then the int value 2 is implicitly widened to double 2.0 when assigned to the double variable result.

Answer

Compilation fails

Answer

2.5

Answer

2

Question 8

A developer writes: String s = "Hello"; s.concat(" World"); System.out.println(s); What is the output?

Accepted Answer

Hello. Strings in Java are immutable. The `concat()` method returns a new string but does not modify the original string `s`. Since the return value is not assigned to any variable, the original string `s` remains unchanged, so `System.out.println(s)` prints "Hello".

Answer

Compilation fails

Answer

Hello World

Answer

Hello World

Question 9

Given: String str = "Java"; str = str.concat(" SE"); str.replace('a', 'A'); System.out.println(str); What is the output?

Accepted Answer

Java SE. The `concat` method returns a new String "Java SE" which is assigned back to `str`. The `replace` method also returns a new String but its result is not assigned to any variable, so the original `str` remains unchanged. The final `println` outputs the current value of `str`, which is "Java SE".

Answer

Java

Answer

JAVA SE

Answer

JAvA SE

Question 10

Which operator is used to compare two strings for value equality in Java?

Accepted Answer

equals(). The equals() method in Java's String class compares the actual character sequences of two strings for value equality. Unlike the == operator, which checks reference equality (whether two references point to the same object in memory), equals() performs a lexicographic comparison of the string contents, returning true if and only if both strings have the same length and the same characters in the same order.

Answer

compareTo()

Answer

=

Answer

==

Question 11

What is the result of: System.out.println(10 + 20 + "30");

Accepted Answer

3030. In Java, the '+' operator is left-associative. The expression `10 + 20 + "30"` is evaluated as `(10 + 20) + "30"`, which first performs integer addition to get `30`, then concatenates that integer with the string `"30"`, resulting in the string `"3030"`. The `System.out.println` method then prints the string `3030`.

Answer

102030

Answer

30

Answer

Compilation fails

Question 12

Given: boolean a = false; boolean b = true; boolean c = true; System.out.println(a || b && c); What is the output?

Accepted Answer

true. In Java, the logical AND operator (&&) has higher precedence than the logical OR operator (||). Therefore, the expression `a || b && c` is evaluated as `a || (b && c)`. Given `a = false`, `b = true`, and `c = true`, `b && c` evaluates to `true`, and then `false || true` evaluates to `true`. Thus, the output is `true`, making option D correct.

Answer

false

Answer

Compilation fails

Answer

None of the above

Question 13

Which of the following is a valid Java identifier?

Accepted Answer

_myVar. (_myVar) is a valid Java identifier because it starts with an underscore, which is permitted by the Java Language Specification. Java identifiers must begin with a letter (A-Z, a-z), dollar sign ($), or underscore (_), and cannot start with a digit or contain hyphens. The underscore is explicitly allowed, making _myVar a legal identifier.

Answer

2variable

Answer

class

Answer

my-var

Question 14

What is the output of: int i = 1; i = i++; System.out.println(i);

Accepted Answer

1. In Java, the expression `i = i++` uses the post-increment operator, which first stores the current value of `i` (1) for the assignment, then increments `i` to 2, but the stored original value (1) is then assigned back to `i`. Thus, `i` remains 1, and the output is 1.

Answer

Compilation fails

Answer

0

Answer

2

Question 15

Which primitive type can store a single character?

Accepted Answer

char. The `char` primitive type in Java is specifically designed to store a single 16-bit Unicode character, ranging from '\u0000' (0) to '\uffff' (65535). It is the only primitive type that directly represents a character value, making it the appropriate choice for storing a single character.

Answer

String

Answer

byte

Answer

short

Question 16

Given: double d = 5.0; int i = d; What is the result?

Accepted Answer

Compilation fails. In Java, assigning a double to an int without an explicit cast causes a compilation error because double is a 64-bit floating-point type and int is a 32-bit integer type. Java does not allow implicit narrowing conversions due to potential loss of precision, so the code fails to compile.

Answer

5.0

Answer

5

Answer

Runtime error

Question 17

What is the default value of a boolean variable in Java?

Accepted Answer

false. In Java, the default value of a boolean variable (when declared as a class field or instance variable) is 'false'. This is specified by the Java Language Specification (JLS §4.12.5), which defines default values for all primitive types. Unlike local variables, which must be explicitly initialized, instance and static variables receive default values automatically.

Answer

null

Answer

true

Answer

0

Question 18

Which TWO of the following are valid ways to create a String?

Accepted Answer

String s = new String("Hello");. It uses the `new` keyword to explicitly create a new String object in the heap, which is a valid way to instantiate a String. Option E is correct because it uses a string literal, which is the most common and efficient way to create a String in Java, leveraging the string constant pool.

Answer

String s = 'Hello';

Answer

String s = 123;

Answer

String s = String.valueOf("Hello");

Question 19

Which THREE of the following are valid Java operators?

Accepted Answer

<<. (<<) is correct because it is the Java left shift operator, which shifts the bits of an integer or long value to the left by a specified number of positions, filling with zeros. This is a valid bitwise shift operator in Java, defined in the Java Language Specification (JLS §15.19).

Answer

::

Answer

<==

Question 20

Which TWO of the following are primitive data types in Java?

Accepted Answer

double. (double) is correct because double is a 64-bit IEEE 754 floating-point primitive data type in Java, used for decimal values with double precision. Option D (int) is correct because int is a 32-bit signed two's complement integer primitive, the default integer type in Java. Both are part of the eight primitive types defined in the Java Language Specification.

Answer

String

Answer

Integer

Answer

Boolean