Basics Of Java

Question 1

What is Java?

Answer 1

Java is a high-level, object-oriented programming language designed for portability and ease of use.

Question 2

True or False: Java is a platform-independent language.

Answer 2

True

Question 3

Fill in the blank: Java was developed by ________.

Answer 3

Sun Microsystems

Question 4

What is the Java Virtual Machine (JVM)?

Answer 4

The JVM is an abstract computing machine that enables a computer to run Java programs.

Question 5

What is the main method signature in Java?

Answer 5

public static void main(String[] args)

Question 6

What does JDK stand for?

Answer 6

Java Development Kit

Question 7

What is the purpose of the JRE?

Answer 7

Java Runtime Environment is used to run Java applications.

Question 8

What are Java bytecodes?

Answer 8

Java bytecodes are the compiled format of Java source code that can be executed by the JVM.

Question 9

Which keyword is used to create a class in Java?

Answer 9

class

Question 10

True or False: In Java, every class must be defined in a separate file.

Answer 10

False

Question 11

What is encapsulation in Java?

Answer 11

Encapsulation is the bundling of data and methods that operate on that data within one unit, restricting access to some of the object’s components.

Question 12

What does the ‘this’ keyword refer to in Java?

Answer 12

‘this’ refers to the current instance of the class.

Question 13

What is inheritance in Java?

Answer 13

Inheritance is a mechanism where one class can inherit fields and methods from another class.

Question 14

What is polymorphism in Java?

Answer 14

Polymorphism allows methods to do different things based on the object that it is acting upon.

Question 15

What is an interface in Java?

Answer 15

An interface is a reference type in Java that can contain only constants, method signatures, default methods, static methods, and nested types.

Question 16

What is the purpose of the ‘final’ keyword?

Answer 16

The ‘final’ keyword is used to declare constants, prevent method overriding, and prevent inheritance.

Question 17

What are the primitive data types in Java?

Answer 17

The primitive data types in Java are byte, short, int, long, float, double, char, and boolean.

Question 18

What is the difference between ‘== ‘and ‘.equals()’ in Java?

Answer 18

’==’ checks for reference equality, while ‘.equals()’ checks for value equality.

Question 19

What is a constructor in Java?

Answer 19

A constructor is a special method that is called when an object is instantiated.

Question 20

What is exception handling in Java?

Answer 20

Exception handling is a mechanism to handle runtime errors, allowing the normal flow of the program to continue.

Question 21

What is the purpose of the ‘try’ block?

Answer 21

The ‘try’ block is used to wrap code that might throw an exception.

Question 22

What is the difference between ‘throw’ and ‘throws’?

Answer 22

‘throw’ is used to explicitly throw an exception, while ‘throws’ is used in method signatures to declare that a method may throw exceptions.

Question 23

What is a collection in Java?

Answer 23

A collection is an object that can hold multiple values, such as lists, sets, and maps.

Question 24

What does the ‘ArrayList’ class do?

Answer 24

ArrayList is a resizable array implementation of the List interface.

Question 25

What is multithreading in Java?

Answer 25

Multithreading is the concurrent execution of two or more threads in a program.

Question 26

True or False: The 'synchronized' keyword is used for thread safety.

Answer 26

True

Question 28

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

Answer 28

false

Question 29

Which of the following is a valid declaration of a char?

Answer 29

char c = 'a';

Question 30

True or False: In Java, all classes inherit from the Object class.

Answer 30

True

Question 31

Fill in the blank: The ______ keyword is used to create a subclass in Java.

Answer 31

extends

Question 32

What is the output of the following code: System.out.println(5 + 10 + 'A');?

Answer 32

15A

Question 33

Which interface does a class implement to be able to use the Collections.sort() method?

Answer 33

Comparable

Question 34

What is the purpose of the 'final' keyword in Java?

Answer 34

To declare constants or prevent method overriding and inheritance.

Question 35

What will happen if you try to compile the following code? int[] arr = new int[5]; arr[5] = 10;

Answer 35

ArrayIndexOutOfBoundsException

Question 36

True or False: Java supports multiple inheritance through classes.

Answer 36

False

Question 37

What is the output of the following code snippet? System.out.println(10 / 3);

Answer 37

3

Question 38

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

Answer 38

String

Question 39

What is the keyword used to handle exceptions in Java?

Answer 39

try

Question 40

Fill in the blank: The ______ method is called when an object is created from a class.

Answer 40

constructor

Question 41

What does JVM stand for?

Answer 41

Java Virtual Machine

Question 42

What is the result of the expression '5 == 5'?

Answer 42

true

Question 43

Which of the following is a correct way to declare an array in Java?

Answer 43

int[] arr = new int[10];

Question 44

True or False: Java is platform-independent due to the use of bytecode.

Answer 44

True

Question 45

What keyword is used to create an interface in Java?

Answer 45

interface

Question 46

What is the output of System.out.println(2 + 3 + "Hello");?

Answer 46

5Hello

Question 47

Which keyword is used to prevent a class from being subclassed?

Answer 47

final

Question 48

What is the purpose of the 'this' keyword in Java?

Answer 48

To refer to the current instance of a class.

Question 49

Which of the following is a valid way to create an instance of a class?

Answer 49

MyClass obj = new MyClass();

Question 50

True or False: A method can have the same name as a class in Java.

Answer 50

True

Question 51

Fill in the blank: The ______ statement is used to exit a loop in Java.

Answer 51

break

Question 52

What is the result of the following code snippet? int x = 10; x += 5; System.out.println(x);

Answer 52

15

Question 53

Which exception is thrown when an array is accessed with an illegal index?

Answer 53

ArrayIndexOutOfBoundsException

Question 54

What is the purpose of the 'super' keyword?

Answer 54

To refer to the superclass of the current object.

Question 55

What is the correct syntax for a for-each loop in Java?

Answer 55

for (Type var : array) { }

Question 56

True or False: A constructor can have a return type.

Answer 56

False

Question 57

Which of the following is a valid statement to create a HashMap?

Answer 57

HashMap map = new HashMap<>();

Question 58

What does the keyword 'static' mean?

Answer 58

The member belongs to the class, rather than instances of the class.

Question 59

What is the output of the following code snippet? System.out.println("Hello".length());

Answer 59

5

Question 60

Fill in the blank: The ______ block is used to handle exceptions in Java.

Answer 60

catch

Question 61

What is polymorphism in Java?

Answer 61

The ability of an object to take on many forms, typically through method overriding or overloading.

Question 62

True or False: The 'instanceof' operator is used to test whether an object is an instance of a specific class.

Answer 62

True

Question 63

What is the output of System.out.println(10 % 3);?

Answer 63

1

Question 64

Which keyword is used to define a constant in Java?

Answer 64

final

Question 65

What does the term 'encapsulation' mean in Java?

Answer 65

The bundling of data with the methods that operate on that data.

Question 66

What is the purpose of the 'abstract' keyword?

Answer 66

To declare a class that cannot be instantiated or a method that must be implemented by subclasses.

Question 67

Fill in the blank: The ______ interface should be implemented to create a thread in Java.

Answer 67

Runnable

Question 68

True or False: Java supports operator overloading.

Answer 68

False

Question 69

What is the output of the following code snippet? System.out.println("A" + "B" + "C");

Answer 69

ABC

Question 70

What is the purpose of the 'volatile' keyword?

Answer 70

To indicate that a variable's value will be modified by different threads.

Question 71

What is the difference between '== and 'equals()' in Java?

Answer 71

'==' checks for reference equality, while 'equals()' checks for value equality.

Question 72

What is the output of System.out.println("5" + 5);?

Answer 72

55

Question 73

Which statement is used to import a package in Java?

Answer 73

import packageName;

Question 74

True or False: Java does not support multiple inheritance.

Answer 74

True

Question 75

Fill in the blank: The ______ keyword is used to create an instance of an interface.

Answer 75

new

Question 76

What does JDK stand for?

Answer 76

Java Development Kit

Question 77

What is the main method signature in Java?

Answer 77

public static void main(String[] args)

Question 78

What is the output of System.out.println(1 + 2 + "3");?

Answer 78

33

Question 79

Which of the following is not a feature of Java?

Answer 79

Pointers

Question 80

True or False: In Java, an abstract class can have concrete methods.

Answer 80

True

Question 81

What is the purpose of the 'synchronized' keyword?

Answer 81

To control access to a method or block by multiple threads.

Question 82

What is the output of the following code snippet? int a = 5; int b = a++; System.out.println(b);

Answer 82

5

Question 83

What does the 'default' keyword do in an interface?

Answer 83

It allows methods to have a body in an interface.

Question 84

Fill in the blank: The ______ keyword is used to call a constructor from another constructor in Java.

Answer 84

this

Question 85

What is a lambda expression in Java?

Answer 85

A concise way to represent a function interface using an expression.

Question 86

What is the output of System.out.println("Hello".substring(1, 4));?

Answer 86

ell

Question 87

True or False: Java supports multiple inheritance through interfaces.

Answer 87

True

Question 88

What is the purpose of the 'transient' keyword?

Answer 88

To indicate that a field should not be serialized.