In this Post, You wil learn about Java Fundamentals Questions And Answer with Easy Understandable for Students. Java is a widely-used object-oriented programming language designed for cross-platform compatibility, stability, and security.
Questions Answer of Java Fundamentals
- What is Java Language?
Ans: Java is a very popular high level programming language and has been used widely to create various types of computer applications such as database applications, desktop applications, Web based applications, mobile applications, and games among others.
- What is High level Programming Language
Ans: High-level language is more readable than assembly. Some high-level languages are also scripting languages, meaning that the code is not compiled until runtime. Examples of high-level languages include: FORTRAN, C, C++, Java, JavaScript, Python.
- Write an Five high level programming language.
Ans: FORTRAN, C, C++, Java, JavaScript, Python
- What is Machine Language?
Ans:- Machine code, also known as machine language, is the elemental language of computers. It is read by the computer’s central processing unit (CPU), is composed of digital binary numbers
- Explain the term of Compiler
Ans: A Java compiler instead of translating Java code to machine language code, translates it into Java Bytecode (a highly optimized set of instructions).
- Define the term Interpreter.
Ans:- Interpreter in Java is a computer program that converts high-level program statement into Assembly Level Language.
- What is Java Virtual Machine?
Ans:- A Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode.
- Explain the term Java IDE
Ans: Java IDE (Integrated Development Environment) is a software application that enables users to write and debug Java programs more easily.
- What is the shortcut key to Run New Project in Java NetBeans?
Ans: F6
- What is the shortcut key to execute or run a File in Java NetBeans?
Ans:- Shift+F6
- What is Comments in Java and how many types of Comments.
Ans:- The Java comments are the statements in a program that are not executed by the compiler and interpreter. There are 2 types of comments in Java.
Questions Answer of Java Fundamentals
- Explain two ways of comments in java programming.
Ans:- Beginning a comment line with two consecutive forward slashes (//)
Writing the comment between the symbols /* and */
- Why do we use comments in a code?
Ans:-
- Comments are used to make the program more readable by adding the details of the code.
- It makes easy to maintain the code and to find the errors easily.
- What are Java package?
Ans:- A package in java is a group of related classes. Package in java can be categorized in two form, built-in package and user-defined package.
- What is class name and package name in Java?
Ans:- In Java, the class name should be the same as the source file name. The package name can be different from either the class or the source file name.
- What is Method in Java
Ans:- A method is a group of statements written to perform specific task. The method body is enclosed with in a pair of curly braces.
Note:- Main is a special method that every Java application must have.
- Which function is used to take output in Java.
Ans:- System.out.println()
- What is the works of println function in Java.
Ans:- A println() in Java is also utilised to display a text on the console, which is the parameter to this method in String.
- What is data types? How many types of Data types in Java.
Ans:- Data types specify the different sizes and values that can be stored in the variable. There are two types of data types in Java:
- Primitive data types: The primitive data types include boolean, char, byte, short, int, long, float and double.
| Data Type | Type of values | Size |
| Byte | Integer | 8-Bit |
| Short | Integer | 16-bit |
| Int | Integer | 32-bit |
| Long | Integer | 64-Bit |
| Float | Floating Point | 32-bit |
| Double | Floating Point | 64-bit |
| Char | Character | 16-bit |
| Boolean | True or False | 1-bit |
- Non-primitive data types: The non-primitive data types include Classes, Interfaces, and Arrays.
- What are variables called in Java?
Ans:- A variable is a placeholder for data that can change its value during program execution. A variable is the name for a storage location in the computer’s internal memory. All data variables in Java have to be declared and initialized before they are used. When declaring variables, we have to specify the data type.
- How many bytes of data does a long data-type store in java?
Ans:- 64-bit
- Which of the following type of values store data type in java
| Data Type | Types of Values | Size |
| Byte | Integer | 8-bit |
| Short | Integer | 16-bit |
| Int | Integer | 32-bit |
| Long | Integer | 64-bit |
| Float | Floating point | 32-bit |
| Double | Floating point | 64-bit |
| Char | Character | 16-bit |
| Boolean | True or false | 1-bit |
Questions Answer of Java Fundamentals
- What are the valid variable rules in Java?
Ans:-
- Variable names can begin with either an alphabetic character , an underscore
(_), or a dollar sign ($). However, convention is to begin a variable name with a
letter . They can consist of only alphabets, digits, and underscore.
- Variable names must be one word. Spaces are not allowed in variable names.
Underscores are allowed. “total_marks” is fine but “total marks” is not.
- There are some reserved words in Java that cannot be used as variable
names, for example – int.
- Java is a case-sensitive language. Variable names written in capital letters
differ from variable names with the same spelling but written in small letters. For
example, the variable name “percentage” differs from the variable name
“PERCENTAGE” or “Percentage”.
- It is good practice to make variable names meaningful. The name should
indicate the use of that variable.
- Define the terms of String variables.
Ans:- A variable of the primitive data type char can be used to store a single character . T o store more than one character , we use the String class in Java. T o assign a text value to a String variable we enclose the text between double quotes.
- What are operators in Java Language?
Ans:- Operators are special symbols in a programming language and perform certain specific operations. For example: +, -, *, / etc.
- How many types of Operators?
Ans:- There are many types of operators in Java which are given below:
Arithmetic Operator(+,-,*,/,%,++,–)- Relational Operator(==, !=, >, <, >=, <=)
- Logical Operator (&&, ||, !)
- Assignment Operator(=, +=, -=, *=, /=, %=)
- What are control flow statements?
Ans:- Java compiler executes the code from top to bottom. Java provides statements that can be used to control the flow of Java code. Such statements are called control flow statements.
- How many types of Control Flow statements provides by Java
Ans:- Java provides three types of control flow statements.
- Decision Making statements
- If-else statements
- switch statement
- Loop statements
- do while loop
- while loop
- for loop
- for-each loop
- Jump statements
- break statement
- continue statement
- Write the term If-Else statements.
Ans:- The Java if statement is used to test the condition. It executes the if block if condition is true otherwise else block is executed.
- Write the syntax of if-else statement with example.
Ans:- The Java if-else statement also tests the condition. It executes the if block if condition is true otherwise else block is executed.
Syntax:
if(condition){
//code if condition is true
}else{
//code if condition is false
}
- What is switch statement?
Ans: The switch statement is used to execute a block of code matching one value out of many possible values.
- What is the meaning of loop?
Ans: Loops in Java is a feature used to execute a particular part of the program repeatedly if a given condition evaluates to be true.
- What is the function of while statements in Java?
Ans:- The while statement evaluates the test before executing the body of a loop.
- Write a square number of program using while loop.
Ans:-
public class WhileDemo {
public static void main (String[ ] args)
{
int number = 1;
while (number <= 5)
{
System.out.print (“Square of ” + number);
System.out.println (” = ” + number*number); ++number;
}
}
}
- Write the steps to be performed to print the squares number from 1 to 5.
Ans:-
The following steps need to be performed.
1. Initialize number = 1
2. Test if the number <= 5
3. If yes, print the square of the number; Increment number (number = number + 1) Go
back to step 2
4. If no, exit the loop.
- What is the use of ++ operator in loop
Ans:- ++ operator is used to increment the value of number.
- Is it same effect ++ number or number++ and number=number+1;
Ans:- Yes
- What is function of Do while loop in Java?
Ans:- The do while statement evaluates the test after executing the body of a loop.
- Write the steps to performed in do-while loop in Java.
Ans:- The following steps need to be performed.
1. Initialize number = 1
2. Print the square of the number
3. Increment number (number = number + 1)
4. Test if the number <= 5
5. If yes, Go back to step 2 If no, Exit the loop
- Difference between while loop and do while loop.
Ans:
| A while loop is an entry controlled loop – it tests for a condition prior to running a block of code | A do-while loop is an exit control loop – it tests for a condition after running a block of code |
| A while loop runs zero or more times Body of loop may never be executed | A do-while loop runs once or more times but at least once |
| The variables in the test condition must be initialized prior to entering the loop structure. | Body of loop is executed at least once |
| while (condition) { statements } | do { statements } while (condition); |
- Write a square number of program using do-while loop.
Ans:-
public class DoWhileDemo {
public static void main (String[ ] args)
{
int number = 1; do
{
System.out.print (“Square of ” + number);
System.out.println (” = ” + number*number); ++number;
}
while (number <= 5);
} }
- Write the common coding errors while using loop.
Ans:- Common Coding Errors –
- Infinite Loops– This type of error occurs when the loop runs forever, the loop never exits. This happens when the test condition is always true.
- Syntax Errors– Do not forget the semi colon at the end of the test condition in a do-while loop. Otherwise you will get a compiler error.
- Do not place a semi colon at the end of the test condition in a while loop.
- Find the Common Coding Errors in For Loop
Ans:-
Common Coding Errors: The for Loop
Initial value is greater than the limit value and the loop increment is positive.
for ( int count = 5; count <= 1; count++)
In this case, body of the loop will never be executed
Initial value is lesser than the limit value and the loop increment is negative.
In this case also, body of the loop will never be executed.
Placing a semicolon at the end of a for statement:
for ( int count = 1; count <= 5; count++);
{
//body of loop
}
This has the effect of defining the body of the loop to be empty . The statements
within the curly braces will be executed only once (after the for loop terminates)
and not as many times as expected.
Executing the loop either more or less times than the desired number of times.
For example, the following loop iterates 4 times and not the intended 5 times
because it exits when count = 5.
for ( int count = 1; count < 5; count ++)
The correct way to loop five times would be to test for count <= 5.
Such errors are known as off by one errors.
Using a loop index (declared within the loop) outside the loop.
for ( int count = 1; count < 5; count ++)
{
System.out.println(count);
}
System.out.println(count); //error!!
The scope of the variable count is only within the body of the loop. It is not visible
outside the loop.
- What is use of for statements(loop) in Java?
Ans:- The for loop is the most widely used Java loop construct. For loop is used to repeat a specific block of code a known number of times.
- Explain the three parts of the for loop.
Ans:-
- The initial_value initializes the value of the loop counter.
- The test_condition tests whether the loop should be executed again. The loop is exited when the test condition fails.
- The step updates the counter in each loop iteration.
- Write a square number of program using for loop.
Ans:-
for (int number = 1; number<= 5; ++number)
{
System.out.print(“Square of “+ number);
System.out.println(” = “+ number*number);
}
- What is role of Arrays?
Ans:- Arrays are variables that can hold more than one value, they can hold a list of values of the same type.
Q48 Write the syntax of Arrays in Java.
Ans:- int[] marks = new int[]{value1, value2, …, valueN};
dataType: This specifies the type of elements the array will hold, like int, double, or String.
arrayName: This is the name you choose for your array variable.
new dataType[]: This uses the new keyword to allocate memory for the array.
value1, value2, …, valueN: These are the actual values you want to store in the array, enclosed in curly braces {}.
Q:- How to Declare and Initialize of an Array?
Ans:-
- Declare the array:
Java
dataType[] arrayName;
This defines a variable arrayName of type array, but doesn’t allocate memory yet.
- Initialize the array:
arrayName = new dataType[size];
Q49 Difference between variable and Arrays .
Ans:- Array holds multiple values, whereas an ordinary variable hold a single value. . A
variable is a field that stores data values during the execution of a Java program.
Ans:-
Common Coding Errors: Arrays
In an off by one error, the loop index if varied from 0 to n instead of 0 to n-1. For example, if the array size is 5, then loop index = 5 is an off by one error since array index can go only from 0 to 4.
double [] ] marks = new double [5];
for (int i = 0; i <= 5; i++) {
System.out.print(marks[i]);
}
In this case an Array index out of bounds error occurs and the program terminates unexpectedly with an error as below.
Exception in thread “main”
java.lang.ArrayIndexOutOfBoundsException: 5
at javaprograms.ArrayDemo.main(ArrayDemo.java:11)
Java Result: 1
Q51 What is use of (\t) syntax?
Ans:- The use of \t to print a tab between the numbers in the print statement
Q52 What is Method in Java?
Ans:- A method is a block of code or collection of statements or a set of code grouped
together to perform a certain task or operation. A method has a name, a return type, an optional list of parameters, and a body. The structure of a Java method is as below:
static double rectangle_area (double length, double breadth)
{
return (length * breadth);
}
Q:- What is the use of Void ?
Ans:- A special return type void can be used if a method does not return any value. For example, a method that just prints a string need not have a return value can use void as the return type.
void print_message(String message) {
System.out.println(“The message is: “+ message);
}
Q53 Explain the term of OOP (Object oriented Programming)
Ans:- Java is an Object Oriented Programming (OOP) language. In an OOP language, a program is collection of objects that interact with other objects to solve a problem. Each object is an instance of a class.
Q54 What is Class and Objects?
Ans:- Objects:– An entity that has state and behavior is known as an object e.g., chair, bike, marker, pen, table, car, etc. A program is collection of objects that interact with other objects to solve a problem. Each object is an instance of a class.
Class :- A class is a group of objects which have common properties. . A class is a
physical or logical entity that has certain attributes. The title, author, publisher, genre and price are the data members of the class Book.
Q55 What is the role of data member and method member in Java?
Ans:- Variables declared with in a class preceded by a data type which define the state of an object are called data members.
Member method are declared where the class is defined. The methods are a member of the class within which they are written.
Public Class Book {
String Title;
String Author; //data member of the book class
String Publisher;
double Price;
void Display() //method member of the book class
{
System.out.println(“Title” “+Title);
System.out.println(“Author” “+Author);
System.out.println(“publisher” “+publisher);
System.out.println(“Price” “+Price);
}}
Q56 What are constructors?
Ans:- A special method member called the constructor method is used to initialize the data members of the class . The constructor has the same name as the class, has no return type, and may or may not have a parameter list.
class Book {
// Member variables
String title;
String author;
// Constructor (no arguments)
Book() {
title = “Unknown”;
author = “Unknown”;
}
// Method to display book details
public void displayDetails() {
System.out.println(“Title: ” + title);
System.out.println(“Author: ” + author);
}
}
public class Main {
public static void main(String[] args) {
// Create a Book object using the constructor
Book book1 = new Book();
// Display book details
book1.displayDetails();
}
}
Explanation:
- We define a class Book with two member variables: title and author.
- The class has a constructor named Book. This constructor has no arguments (indicated by empty parentheses).
- Inside the constructor, we initialize the title and author variables with default values (“Unknown” in this case). This ensures the object has some initial state.
- We also define a method displayDetails to print the book’s title and author.
- In the Main class, we create a new Book object named book1 using the constructor. This calls the Book constructor and creates a new Book instance.
- Finally, we call the displayDetails method on book1 to print its details.
Q57 Define Access modifiers.
Ans:- Access modifiers are keywords that can be used to control the visibility of fields, methods, and constructors in a class. The four access modifiers in Java are public, protected, default, and private.
Note:- Data members of a class can be accessed from outside the class by default. Private members of a class cannot be accessed outside the class.
Q58 What is the use of User Data Input with example?
Ans:-
User Input in Java:
Scanner Class: If you want to get user input from the keyboard, the most common approach is to use the Scanner class from the java.util package.
Scanner Methods: The Scanner class provides various methods for reading different data types entered by the user. For example, nextInt() reads an integer, nextDouble() reads a double, and nextLine() reads a whole line of text (including spaces).
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print(“Enter your name: “);
String name = scanner.nextLine();
System.out.print(“Enter your age: “);
int age = scanner.nextInt();
System.out.println(“Hello, ” + name + “! You are ” + age + ” years old.”);
}
}
Q59 Which packages are used for array manipulation?
Ans:- import Java.util.Arrays
Q60 Which of the method used for sorting a number using array?
Ans:-
double[] marks = {103, 144, 256.5,346, 387.5};
Arrays.sort(marks);
The marks array after sorting becomes = {103.0, 144.0, 256.5, 346.0, 387.5}. Sorting
makes it easier for us to find the lowest and highest marks obtained by a student. To print the lowest marks, we can now write
System.out.println(marks[0]);
To print the highest marks, we can write
System.out.println(marks[marks.length-1]);
The same method can be used to sort an array of Strings in alphabetic order.
String[] names ={ ” M a y a n k ” , ” M u d i t ” , ” S h i v a ” , ” A n j u ” ,”Savita”};
Arrays.sort(names);
Q60 Which packages are used for String manipulation?
Ans:- package Java.lang
Q61 Write a table to show the common used String class methods.
Ans:-
| Method | Description | Application myString =“Hello World” | Output |
| char charAt (int index) | Return the character at the given index | myString.charAt(6) | W |
| String concat (String str) | Concatenate the specified string at the end of this string | myString.concat(”Today”) | Hello World Today |
| boolean contains (String s) | Returns true if this string contains the specified substring | myString.contains (”Hell”) | True |
| boolean endsWith (String suffix) | T est whether this string end with the given suffix | myString.endsWith (”old”) | False |
| boolean equals (Object anObject) | Compare this string with specified object | myString.equals (”Goodbye World”) | False |
| boolean equalsIgnoreCase (String another) | Compare this string with specified string ignoring case | myString. equalsIgnoreCase (”hello world”) | True |
| int indexOf (int c) | Return the index of the first occurrence of given character | myString. indexof (’W’) | 6 |
| int indexOf (String str) | Return the index of the first occurrence of given substring | myString. indexof (”rld”) | 8 |
| boolean isEmpty() | Returns true if the length of this string is 0 | myString. isEmpty() | False |
| int length() | Returns the length of the String | myString. length () | 11 |
| String replace(char oldChar, char newChar) | Returns a new string after replacing all occurrences of oldChar in this string with newChar | myString.replace (‘l’,’*’) | He**o Wor*d |
| String replace(String oldStr, String newStr) | Returns a new string after replacing all occurrences of oldStr in this string with newStr | myString.replace (”Hello”, “Yellow”) | Yellow World |
| String toLowerCase() | Converts all of the characters in this String to lower case | myString.toLower Case ( ) | hello world |
| String toUpperCase() | Converts all of the characters in this String to upper case | myString.toLower Case ( ) | HELLO WORLD |
Q:61 What is Getter and Setter methods in Java?
Ans:- Private data members of a class cannot be accessed outside the class, you can give controlled access to data members outside the class through getter and setter methods.
A getter method returns the value of a data member. For example we could
define a getter method in the Book class for the price data member as given below:
double getPrice ( ) {
return price;
}
Similarly , we define a setter method but control how the price is set. We do not allow a book price to become lower than 100.0
void setPrice(double newprice) {
if (newprice < 100)
System.out.println(“Price cannot be set lower than
100!”);
else
price = newprice;
}
Q62 Define the term Exception Handling.
Ans:- The Exception Handling in Java is one of the powerful mechanism to handle the
runtime errors so that the normal flow of the application can be maintained.
Q62 Which keyword used to handle an exception in Java?
Ans:- Java provides three keywords that are used to handle the exception.
- Try
- Catch
- Finally
Q63 Explain Try and catch keyword.
Ans:- try– A try block surrounds the part of the code that can generate exception
catch– The catch blocks follow a try block. A catch block contains the exception
handler – specific code that is executed when the exception occurs. Multiple catch
blocks following a try block can handle different types of exceptions.
Q64 Write the example of Java Exception Handling
Ans:- Java Exception Handling Example
Let’s see an example of Java Exception Handling in which we are using a try-catch
statement to handle the exception.
JavaExceptionExample.java
public classJavaExceptionExample{
public static voidmain(String args[]){
try{
//code that may raise exception
intdata=100/0;
}catch(ArithmeticException e){System.out.println(e);}
//rest code of the program
System.out.println(“rest of the code…”);
}
}
Q65 Write the following terms –
a. Assertions
b. Threads
c. Wrapper class
Ans:-
Assertions :-An assertion is a useful mechanism for effectively identifying/detecting and correcting logical errors in a program.
Threads :- A multithreaded program is one that can perform multiple tasks concurrently so that there is optimal utilization of the computer’s resources. A multithreaded program consists of two or more parts called threads each of which can execute a different task independently at the same time.
In Java, threads can be created in two ways
1. By extending the Thread class
2. By implementing the Runnable interface
Wrapper Class:- By default, the primitive datatypes (such as int, float, and so on) of Java are passed by value and not by reference. Sometimes, you may need to pass the primitive datatypes by reference. That is when you can use wrapper classes provided by Java. These classes wrap the primitive datatype into an object of that class.
public class Car {
// Member variable using a primitive type (int)
private int speed;
// Constructor (no arguments)
public Car() {
speed = 0;
}
// Setter method using a wrapper class (Integer)
public void setSpeed(Integer newSpeed) {
// Validate speed (optional)
if (newSpeed < 0) {
System.out.println(“Error: Speed cannot be negative.”);
return;
}
speed = newSpeed.intValue(); // Unboxing to access the primitive value
}
// Getter method using a wrapper class (Integer)
public Integer getSpeed() {
return Integer.valueOf(speed); // Boxing to create an Integer object
}
// Method to accelerate (demonstrates using the primitive value)
public void accelerate() {
speed += 10;
}
}
public class Main {
public static void main(String[] args) {
Car car = new Car();
// Set speed using setter (with validation)
car.setSpeed(50);
System.out.println(“Current speed: ” + car.getSpeed() + ” mph”); // Get speed using getter
car.accelerate();
System.out.println(“Speed after acceleration: ” + car.getSpeed() + ” mph”);
}
}