Java Variables, Data Types & Type Casting Quiz

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40 focused questions Java primitive and reference types, variable declaration rules, widening/narrowing conversions, the final keyword, and the most common type-casting pitfalls.

40 Questions

~80 minutes

Question 1

How many primitive data types does Java have?

Question 2

What is the default value of an instance int variable?

null

Compilation error if not initialized

undefined

Question 3

What is the output of this code?

java

byte b = 127;
b = (byte)(b + 1);
System.out.println(b);

-128

128

Compilation error

127

Question 4

Which of these is a reference type?

String

int

char

boolean

Question 5

What happens when this code is compiled?

java

float f = 3.14;

Compilation error — double literal cannot be assigned to float without suffix or cast

Compiles successfully

Runtime exception

f becomes exactly 3.14

Question 6

What does the final keyword do when applied to a primitive variable?

Makes the variable immutable — its value cannot be changed after initialization

Makes it thread-safe

Gives it a default value

Only works on local variables

Question 7

What is the output?

java

long l = 100L;
int i = (int) l;
System.out.println(i);

100

Compilation error

100L

Question 8

Which statement about var is true?

It can only be used for local variables, not fields or parameters

It makes the variable dynamically typed

It can be used without an initializer

It was added in Java 5

Question 9

What is the result of this autoboxing/unboxing example?

java

Integer a = 1000;
Integer b = 1000;
System.out.println(a == b);

false

true

Compilation error

Runtime exception

Question 10

What does final do when applied to a reference variable?

The reference cannot point to a different object, but the object itself can be mutated

The object becomes completely immutable

Only works with primitives

Prevents the object from being garbage collected

Question 11

What is the output?

java

char c = 'A';
int i = c + 1;
System.out.println((char)i);

Compilation error

Question 12

Which conversion requires an explicit cast?

int → short

byte → int

short → long

float → double

Question 13

What happens here?

java

double d = 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1 + 0.1;
System.out.println(d == 1.0);

false

true

Compilation error

0.0

Question 14

What is the default value of a boolean instance variable?

false

true

null

Compilation error

Question 15

What is the result of this compound assignment?

java

byte b = 10;
b += 1000;
System.out.println(b);

Compilation error without cast

1074

-106 (overflow)

Question 16

Which of these declarations is invalid?

var x;

var x = 10;

var list = new ArrayList<>();

var n = null;

Question 17

What is printed?

java

final StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb);

Hello World

Hello

Compilation error

Runtime exception

Question 18

What is the size of a long variable?

64 bits

32 bits

Platform dependent

16 bits

Question 19

What is the output of this unboxing null scenario?

java

Integer i = null;
int j = i;
System.out.println(j);

Throws NullPointerException at runtime

Prints 0

Compilation error

Prints null

Question 20

Which cast will compile successfully?

java

Number n = Integer.valueOf(42);
Double d = (Double) n;

None — throws ClassCastException at runtime

Compiles and runs fine

Compilation error

Only works with primitives

Question 21

Can a local variable be declared final?

Yes, and it's commonly used with lambdas and effectively final rules

No, final is only for fields

Only in try-with-resources

Only for static variables

Question 22

What is the range of byte?

-128 to 127

0 to 255

-127 to 128

-256 to 255

Question 23

What is printed?

java

int x = 10;
double d = x;
System.out.println(d);

10.0

Compilation error

10.00

Question 24

Which literal represents a long value?

100L

100

100l (lowercase L)

100.0

Question 25

What is the output of this classic precision loss example?

java

int i = 123456789;
float f = i;
int back = (int) f;
System.out.println(i - back);

Some non-zero value (e.g., 1 or -1)

Compilation error

123456789

Question 26

Can a final variable be a blank final (uninitialized at declaration)?

Yes, if it's an instance or static field and initialized in constructor or static block

No, final must always have a value at declaration

Only for local variables

Only in interfaces

Question 27

What is printed?

java

boolean b = false;
if (b = true) {
    System.out.println("True");
} else {
    System.out.println("False");
}

True

False

Compilation error

No output

Question 28

Which of these is NOT a widening conversion?

double → float

int → long

byte → short

char → int

Question 29

What is the output?

java

final int[] arr = {1, 2, 3};
arr[0] = 99;
System.out.println(arr[0]);

Compilation error

ArrayIndexOutOfBoundsException

Question 30

Why does this fail to compile?

java

var x = 10;
x = "hello";

var infers int — second assignment is incompatible

var is not allowed in methods

String must be in quotes

var can only be used once

Question 31

What is the literal type of 0b1010?

int (binary literal)

byte

long

Binary not supported

Question 32

What is printed?

java

System.out.println(0.1 + 0.2 == 0.3);

false

true

Compilation error

0.3

Question 33

Which wrapper class has a cache larger than -128 to 127 by default?

None — only Integer caches that range by default

Long

Boolean

Character (0-127)

Question 34

What is the output?

java

char c = 65;
System.out.println(c);

Compilation error

null

Question 35

Why does this compile without error?

java

short s = 100;
s += 500;
System.out.println(s);

Compound assignment operators perform automatic narrowing cast

short can hold 600

int is promoted to short

Compilation error

Question 36

What is the default value of a reference type instance variable?

null

Compilation error

empty object

Question 37

What is printed?

java

final var list = java.util.List.of(1, 2, 3);
// list.add(4);
System.out.println(list);

[1, 2, 3]

Compilation error on var

Empty list

Runtime exception

Question 38

Which of these assignments requires a cast?

long l = 1234567890123;

int i = 100;

float f = 3.14f;

double d = 3.14;

Question 39

What is the result?

java

Object obj = "Hello";
String s = (String) obj;
System.out.println(s.toUpperCase());

HELLO

ClassCastException

Compilation error

null

Question 40

Why is understanding primitive vs reference types crucial in Java?

It affects memory usage, nullability, performance, and how equality/comparison works

Only reference types can be used in collections

Primitives cannot be passed to methods

Reference types are slower always

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Java Variables, Data Types & Type Casting Quiz

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Question 15

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Question 31

Question 32

Question 33

Question 34

Question 35

Question 36

Question 37

Question 38

Question 39

Question 40

About This Variables & Data Types Quiz

What You Will Practise

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