primitives

Question 1

What are the 3 primitive types tested on the AP CSA exam?

Answer 1

int, double, boolean

Question 2

What keyword is used to declare a variable in Java?

Answer 2

No keyword is required. Just write the type:

Example: int x = 5;

Question 3

What does the = operator do?

Answer 3

Assigns the value on the right to the variable on the left.

Question 4

What is the default value of an uninitialized primitive variable?

Answer 4

Primitive variables must be initialized before use in local scope. (No default.)

Question 5

What is the result of 7 / 2 in Java?

Answer 5

3 — Integer division truncates decimal.

Question 6

What is the result of 7.0 / 2 in Java?

Answer 6

3.5 — If either operand is double, result is double.

Question 7

What does the % operator do?

Answer 7

Modulo — returns the remainder.

Example: 7 % 2 = 1

Question 8

What is a compound assignment operator?

Answer 8

Shortcuts like x += 1; which means x = x + 1;

Question 9

What does x++ do?

Answer 9

Increments x by 1 (post-increment).

Question 10

How do you cast a double to an int?

Answer 10

(int) 3.8 results in 3 — truncates the decimal.

Question 11

What is the difference between int and double in Java?

Answer 11

int = whole numbers; double = decimal values.

Question 12

What does boolean represent?

Answer 12

Either true or false.

Question 13

What happens if you try to divide by 0 in Java?

Answer 13

For integers: runtime error (ArithmeticException). For doubles: Infinity or NaN.

Question 14

What is an object in Java?

Answer 14

An instance of a class.

Question 15

How do you create an object?

Answer 15

ClassName obj = new ClassName();

Question 16

What is a constructor?

Answer 16

A special method that initializes a new object.

Question 17

Can constructors have parameters?

Answer 17

Yes!

Example: new Dog(“Fido”);

Question 18

What keyword is used to refer to the current object?

Answer 18

this

Question 19

Can a class have more than one constructor?

Answer 19

Yes — this is called overloading.

Question 20

What is a method?

Answer 20

A function defined in a class, which can be called on objects.

Question 21

How do you call a method that returns no value?

Answer 21

obj.methodName(); — must match parameters.

Question 22

What is the difference between a void method and a non-void method?

Answer 22

Void = no return value; non-void = returns something (like int, String, etc.)

Question 23

How do you store the result of a method call that returns a value?

Answer 23

int result = obj.getValue();

Question 24

Are strings primitives in Java?

Answer 24

No — String is a reference type (class).

Question 25

How do you declare a String variable?

Answer 25

String name = "Java";

Question 26

What does s.length() return?

Answer 26

The number of characters in the string s.

Question 27

What does s.substring(1, 3) return if s = "Hello"?

Answer 27

"el" (start at index 1, up to but not including index 3)

Question 28

How are string characters indexed in Java?

Answer 28

Zero-based indexing: first character is at index 0.

Question 29

How do you compare strings for equality?

Answer 29

Use .equals() — not ==

Question 30

What does "Hello".indexOf("l") return?

Answer 30

2 — index of the first occurrence of "l"

Question 31

What does "Hi" + 5 evaluate to?

Answer 31

"Hi5" — the number is converted to a string.

Question 32

What are wrapper classes for int and double?

Answer 32

Integer and Double

Question 33

What method converts a string to an integer?

Answer 33

Integer.parseInt("123") → 123

Question 34

What method converts a string to a double?

Answer 34

Double.parseDouble("3.14") → 3.14

Question 35

Are wrapper classes needed for arrays or ArrayLists of primitives?

Answer 35

Yes — ArrayLists cannot store primitives directly. Use wrapper classes.

Question 36

What is Math.pow(2, 3)?

Answer 36

8.0 — Raises 2 to the power of 3

Question 37

What is Math.sqrt(16)?

Answer 37

4.0

Question 38

What is Math.abs(-10)?

Answer 38

10

Question 39

What does Math.random() return?

Answer 39

A double from 0.0 (inclusive) to 1.0 (exclusive)

Question 40

How do you generate a random int from 1 to 6?

Answer 40

(int)(Math.random() * 6) + 1