Practice · Java Basics: Class Structure, Variables, and Data Types

Q1

An object is an instance of a ________.

A program B data value C method D class

Q2

Which line correctly declares and initialises a variable holding a whole number of students?

A int students = 40; B Int students = 40; C int students == 40; D students = int 40;

Q3

What is the default value of an int instance variable that the programmer does not initialise?

A null B 0 C undefined D The code does not compile.

Q4

Analyse the following code. What is the output?

public class Test {
    int x;
    public static void main(String[] args) {
        Test test = new Test();
        System.out.println(test.x);
    }
}

A Compile error: Test has no no-argument constructor. B Compile error: x has not been initialised. C It compiles, runs and displays 0. D Compile error: a class cannot create an object of itself.

Q5

What is the output of the following program?

public class Question4 {
    public static void main(String args[]) {
        String tree = "pine";
        int count = 0;
        if (tree.equals("pine")) {
            int height = 55;
            count = count + 1;
        }
        System.out.print(height + count);
    }
}

A 1 B 55 C 56 D It does not compile.

Q6

Which of the following is not a primitive type in Java?

A char B boolean C String D double

Q7

How many bits does a Java int occupy?

A 8 B 16 C 32 D 64

Q8

Which type would you choose for a population count of 8 billion?

A int B long C short D byte

Q9

Which declaration does not compile?

A long distance = 10000000000L; B long distance = 10000000000; C double d = 5; D int i = 'A';

Q10

Which declaration does not compile?

A float rate = 2.5f; B float rate = 2.5; C double rate = 2.5; D float rate = 2;

Q11

What is the type of the literal 7 in double x = 7;?

A double, because x is a double B int, which is then widened to double C float D long

Q12

Which statement about boolean is correct?

A It can hold 0 or 1. B It can hold only true or false. C Its default value for a field is true. D It occupies 32 bits and holds any integer.

Q13

Which of the following correctly declares a character variable?

A char c = "A"; B char c = 'A'; C char c = A; D Char c = 'A';

Q14

What is the effect of the keyword final on a variable?

A It makes the variable private. B It prevents the variable from being assigned a second time. C It makes the variable static. D It gives the variable a default value.

Q15

Which of these follows the standard Java naming convention for a constant?

A maxSize B MaxSize C MAX_SIZE D max-size

Q16

Which of the following compiles?

A final int N; N = 5; B final int N = 5; N = 6; C final int N = 5; N++; D final int N = 5, N = 6;

Q17

What is wrong with the following code?

public static void main(String[] args) {
    int total;
    System.out.println(total);
}

A Nothing; it prints 0. B total is a local variable and has not been initialised, so it does not compile. C total must be declared final. D println cannot print an int.

Q18

What value of k does the second println statement print?

public class Foo {
    static int i = 0;
    static int j = 0;
    public static void main(String[] args) {
        int i = 2;
        int k = 3;
        {
            int j = 3;
            System.out.println("i + j is " + i + j);
        }
        k = i + j;
        System.out.println("k is " + k);   // second println
        System.out.println("j is " + j);
    }
}

A 0 B 1 C 2 D 3

Q19

In the program of the previous question, what does the first println print?

A i + j is 5 B i + j is 23 C i + j is 6 D The code does not compile.

Q20

Which statement about variable scope is true?

A A variable declared in a method is visible in every method of the class. B A variable declared inside a block is visible only until the block's closing brace. C Two local variables with the same name may be declared in the same block. D Scope has no effect on compilation.

Q21

Which statement declares three int variables in one line, initialising only the first?

A int a = 1, b, c; B int a = 1; b; c; C int a, b, c = 1, 2; D int a = 1 b = 2 c;

Q22

Which of the following is a valid variable declaration?

A int 1stPlace = 1; B double my-total = 3.0; C String firstName = "Ali"; D boolean class = true;

Q23

What does the following statement print?

System.out.println("Total: " + 5 + 3);

A Total: 8 B Total: 53 C Total: 5 3 D The code does not compile.

Q24

And this one?

System.out.println("Total: " + (5 + 3));

A Total: 8 B Total: 53 C Total: 5 3 D The code does not compile.

Q25

What is stored in c after char c = 66;?

A 66 B 'B' C '6' D It does not compile.

Q26

Which line does not compile?

int a = 5;        // L1
double b = a;     // L2
int c = b;        // L3
char d = 'x';     // L4

A L1 B L2 C L3 D L4

Q27

A variable of type String stores:

A the characters themselves inside the variable; B a reference to a String object; C a single Unicode character; D a primitive value.

Q28

Which of the following is the correct way to write a comment that spans three lines?

A // line1 line2 line3 B /* line1 ... line3 */ C  D # line1 ... line3

Q29

What is the value of x after int x = 1_000_000;?

A One million B It does not compile C 1 D Zero

Q30

Which of the following statements about System.out.println is correct?

A System is a method and out is a class. B System is a class, out is an object inside it and println is a method called on that object. C println is a keyword. D It can print only String values.

Q31

An instance variable differs from a local variable because:

A it is declared inside a method; B it is declared in the class body, receives a default value, and exists as long as the object exists; C it cannot be private; D it cannot be used in main.

Q32

What is printed?

public class Counter {
    public static void main(String[] args) {
        int count = 0;
        for (int i = 0; i < 3; i++) {
            int inner = 0;
            inner++;
            count++;
        }
        System.out.print(count);
    }
}

A 0 B 1 C 3 D It does not compile.

Q33

In the previous question, what would System.out.print(inner) after the loop cause?

A It prints 1 B It prints 3 C A compile-time error D A run-time error

Q34

Which pair of values could be stored in a byte?

A −200 and 200 B 0 and 127 C 0 and 300 D −32768 and 32767

Q35 Short answer

Explain the difference between declaring, initialising and assigning a variable, giving one line of Java for each.

Q36 Short answer

Why does Java require an explicit cast for int x = someDouble; but not for double y = someInt;?

Q37 Short answer

Give two reasons why a programmer should write final double VAT_RATE = 0.06; instead of writing 0.06 in five different places.

Q38 Programming

Write a class CircleInfo whose main method declares a final double PI = 3.14159, a radius of 7.5, and prints the diameter, circumference and area on three labelled lines using println.