1Z0-811 Primitives, Strings and Operators Practice Test 3 — 15 Questions

Question 1

A developer is working with Java primitive types and needs to select two statements that correctly describe default values for instance variables (fields) of primitive types. (Choose two.)

Accepted Answer

An instance variable of type int defaults to 0.. Instance variables of primitive types are initialized to default values: boolean to false, and numeric types to zero (int to 0, double to 0.0, etc.). The char type defaults to the null character '\u0000', not '0'. Reference types like String default to null. Therefore, the two correct statements are that boolean defaults to false and int defaults to 0.

Answer

An instance variable of type char defaults to '0'.

Answer

An instance variable of type double defaults to 0.0.

Answer

An instance variable of type String defaults to an empty string "".

Question 2

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 3

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 4

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 5

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 6

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 7

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 8

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 9

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 10

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 11

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 12

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 13

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

Question 14

Which THREE of the following expressions evaluate to true? (Assume int a=5, b=10)

Accepted Answer

a < b. The expression 'a < b' compares the integer values of a (5) and b (10). Since 5 is less than 10, the relational operator '<' returns the boolean value true.

Answer

a == b

Answer

a >= b

Question 15

What is the value of y after executing the following code?
```java
int y = 10 + 12;
```

Accepted Answer

22. The code snippet `int y = 10 + 12;` performs integer addition, resulting in y = 22. Java's primitive arithmetic follows standard rules, so adding 10 and 12 yields 22 without any overflow or conversion issues.

Answer

20

Answer

21

Answer

23