SY.Bsc.Cs Sem-3 Based on Mumbai Unversity
Java Based Application Development (Uint-1) Question Bank Answer:-
1 Write a short note on Java Development Kit.
Ans:
The Java Development Kit (JDK) is a comprehensive software development environment used for building and running Java applications. It is an essential toolkit for Java developers and includes various components to support the entire development lifecycle, from writing and compiling code to debugging and running Java programs.
The key components of the JDK include:
Java Compiler (javac): Converts Java source code (.java files) into bytecode (.class files) that can be executed by the Java Virtual Machine (JVM).
Java Runtime Environment (JRE): The JRE contains the libraries and components needed to run Java applications. It includes the JVM, core classes, and supporting files.
Java Virtual Machine (JVM): The JVM is responsible for running Java bytecode. It provides platform independence, allowing Java applications to run on any device that has a JVM installed.
Development Tools: The JDK includes several tools that help developers:
- javap: A class file disassembler.
- javadoc: A tool to generate API documentation in HTML format.
- jdb: A debugger to troubleshoot and debug Java programs.
- jar: A tool to package Java class files into JAR (Java Archive) files, which can be distributed easily.
Additional Tools: The JDK also provides monitoring tools such as jconsole and profiling tools to check application performance, memory usage, etc.
The JDK is available in different versions such as Standard Edition (SE), Enterprise Edition (EE), and Micro Edition (ME), catering to different use cases from general desktop application development to large-scale enterprise systems.
2 Enlist and Explain Features of Java.
Ans:
Java is a widely-used programming language with several distinctive features that make it popular among developers. The key features of Java are:
Simple: Java is designed to be easy to learn and use. Its syntax is clean, and complex features like pointers and operator overloading (found in C++) are removed, making Java simpler to understand.
Object-Oriented: Java follows the Object-Oriented Programming (OOP) paradigm. This means everything in Java revolves around objects and classes, promoting modular, reusable, and organized code.
Platform-Independent: Java is often referred to as "write once, run anywhere" (WORA). This is due to its ability to compile code into platform-independent bytecode, which can be executed on any device with a Java Virtual Machine (JVM), regardless of the underlying operating system.
Secure: Java includes features that ensure the security of applications, such as the absence of pointers, runtime security checks, and the use of the Java Security Manager, which defines access levels for classes.
Robust: Java has strong memory management, garbage collection, and exception handling features. This helps prevent system crashes and ensures the reliability of the application.
Multithreaded: Java has built-in support for multithreading, allowing developers to write programs that can perform multiple tasks simultaneously, improving the efficiency of applications.
Portable: Java bytecode is platform-independent, making Java programs highly portable across different hardware architectures. This is facilitated by the JVM, which abstracts the underlying system differences.
High Performance: Although Java is interpreted, it offers high performance due to features like Just-In-Time (JIT) compilers, which convert bytecode into machine code at runtime, making execution faster.
3 Write short note on Tokens in Java.
Ans:
In Java, tokens are the smallest elements of a program that the compiler recognizes. Java programs are written using these tokens, which are used to construct statements and expressions. The main types of tokens in Java include:
Keywords: These are reserved words in Java that have predefined meanings in the language and cannot be used as identifiers (variable names, class names, etc.). Examples include
if,else,class,int,return,static,public, etc.Identifiers: Identifiers are names given to various program elements like variables, classes, methods, and arrays. They must start with a letter, dollar sign (
$), or underscore (_), and can be followed by letters, digits, underscores, or dollar signs. For example:myVariable,MainClass, etc.Literals: These are constant values directly represented in the code. Java supports different types of literals, such as:
- Integer Literals (e.g.,
100,0x1Ffor hexadecimal) - Floating-point Literals (e.g.,
3.14,2.5e-3) - Character Literals (e.g.,
'a','\n') - String Literals (e.g.,
"Hello, World!") - Boolean Literals (
true,false)
- Integer Literals (e.g.,
Operators: Operators are symbols that perform specific operations on operands (data values). They include:
- Arithmetic Operators:
+,-,*,/,% - Relational Operators:
==,!=,>,<,>=,<= - Logical Operators:
&&,||,! - Assignment Operators:
=,+=,-=, etc. - Bitwise Operators:
&,|,^,~, etc.
- Arithmetic Operators:
Separators (or Delimiters): These symbols are used to separate code elements. Common separators include:
- Parentheses:
() - Braces:
{}(used for blocks of code) - Square Brackets:
[](used for arrays) - Semicolon:
;(used to terminate statements) - Comma:
,(used to separate variables in a list)
- Parentheses:
Comments: Comments are not tokens that the compiler processes but are used by programmers to include explanations or notes in the code. Java supports:
- Single-line comments:
// - Multi-line comments:
/* ... */ - Documentation comments:
/** ... */(used for generating API documentation)
- Single-line comments:
4 Explain OOPS Pillars in detail.
Ans:
The core principles of Object-Oriented Programming (OOP) are based on four key pillars that enable modular, reusable, and maintainable code. These pillars are:
Encapsulation:
- Definition: Encapsulation refers to the bundling of data (variables) and methods (functions) that operate on the data into a single unit, known as a class. It restricts direct access to some of an object's components, which is the basis for data hiding.
- Purpose: It protects an object's data from unauthorized access or modification and allows controlled access through methods (getters and setters).
- Example
Abstraction:
- Definition: Abstraction is the process of hiding complex implementation details and showing only the essential features of an object. It allows focusing on what an object does rather than how it does it.
- Purpose: Abstraction reduces complexity by allowing developers to interact with objects at a high level, without needing to understand their internal workings.
- Example:
abstract class Animal {// abstract method (no implementation)public abstract void sound();}class Dog extends Animal {public void sound() {System.out.println("Bark");}}Inheritance:
- Definition: Inheritance is a mechanism where one class (subclass or child class) can acquire the properties and behaviors (methods and variables) of another class (superclass or parent class). It promotes code reusability and establishes a relationship between the classes.
- Purpose: Inheritance allows you to create new classes based on existing ones, which leads to a hierarchical structure and promotes reusability and maintainability.
- Example:
class Animal {public void eat() {System.out.println("This animal eats food.");}}class Dog extends Animal {public void bark() {System.out.println("The dog barks.");}}Polymorphism:
- Definition: Polymorphism allows objects to be treated as instances of their parent class, enabling one interface to be used for a general class of actions. It means "many forms" and allows methods to do different things based on the object that invokes them.
- Types:
- Compile-time (Method Overloading): Multiple methods with the same name but different parameter lists exist in the same class.
- Runtime (Method Overriding): A subclass provides a specific implementation of a method already defined in its parent class.
- Purpose: Polymorphism enables flexibility and extensibility in code, allowing objects of different types to be treated in the same way.
- Example (Method Overriding):
class Animal {public void sound() {System.out.println("Some generic animal sound");}}class Dog extends Animal {public void sound() {System.out.println("Bark");}}class Cat extends Animal {public void sound() {System.out.println("Meow");}}public class TestPolymorphism {public static void main(String[] args) {Animal myDog = new Dog(); // upcastingAnimal myCat = new Cat(); // upcastingmyDog.sound(); // Outputs: BarkmyCat.sound(); // Outputs: Meow}}
5 Explain Constructor and its types in java.
Ans:
In Java, a constructor is a special method that is invoked when an object of a class is created. Its primary purpose is to initialize the object’s attributes and allocate resources. Unlike regular methods, constructors have the same name as the class and do not have a return type.
Types of Constructors:
Default Constructor:
- Definition: A constructor that does not take any parameters. If no constructor is defined in a class, Java provides a default constructor automatically.
- Purpose: It initializes object attributes with default values (0, null, or false, depending on the type).
- Example:
Parameterized Constructor:
- Definition: A constructor that takes parameters to initialize an object with specific values provided at the time of object creation.
- Purpose: It allows the creation of objects with initial values defined by the user.
- Example:
Copy Constructor (not a built-in concept in Java, but can be implemented):
- Definition: A constructor that creates a new object as a copy of an existing object.
- Purpose: It is useful for creating a new instance that has the same attributes as another instance of the same class.
- Example:
6 Explain Method Overloading in java with an example.
Ans:
Method Overloading is a feature in Java that allows a class to have more than one method with the same name, provided that they have different parameter lists. This means that you can define multiple methods with the same name but with different types, number of parameters, or both. Method overloading is a way to achieve compile-time polymorphism.
Key Points of Method Overloading:
- Same Method Name: All overloaded methods must have the same name.
- Different Parameters: They must differ in the type, number, or order of parameters.
- Return Type: The return type can be the same or different, but it does not contribute to overloading.
- Compile-Time Polymorphism: The method that gets invoked is determined at compile time based on the method signature.
Example of Method Overloading:
Here’s a simple example demonstrating method overloading in a class:
class Calculator {
// Method to add two integers
int add(int a, int b) {
return a + b;
}
// Overloaded method to add three integers
int add(int a, int b, int c) {
return a + b + c;
}
// Overloaded method to add two double values
double add(double a, double b) {
return a + b;
}
// Overloaded method to add two strings
String add(String a, String b) {
return a + b;
}
}
public class TestMethodOverloading {
public static void main(String[] args) {
Calculator calc = new Calculator();
// Calling different overloaded methods
System.out.println("Sum of 2 and 3: " + calc.add(2, 3)); // Calls add(int, int)
System.out.println("Sum of 1, 2, and 3: " + calc.add(1, 2, 3)); // Calls add(int, int, int)
System.out.println("Sum of 2.5 and 3.5: " + calc.add(2.5, 3.5)); // Calls add(double, double)
System.out.println("Concatenation of Hello and World: " + calc.add("Hello, ", "World!")); // Calls add(String, String)
}
}
7 Explain Method Overriding in java with an example.
Ans:
Method Overriding is a feature in Java that allows a subclass (child class) to provide a specific implementation of a method that is already defined in its superclass (parent class). When a subclass overrides a method, it means that it is replacing the superclass's implementation of that method with its own version.
Key Points of Method Overriding:
- Same Method Name and Parameters: The method in the subclass must have the same name, return type, and parameter list as the method in the superclass.
- Runtime Polymorphism: Method overriding is a way to achieve runtime polymorphism. The method that gets invoked is determined at runtime based on the object type.
- Use of
@OverrideAnnotation: While not mandatory, it is a good practice to use the@Overrideannotation to indicate that a method is overriding a superclass method. This helps with code readability and catches errors at compile time if the method does not actually override any method.
Example of Method Overriding:
Here’s a simple example demonstrating method overriding in Java:
// Parent class
class Animal {
void sound() {
System.out.println("Some generic animal sound");
}
}
// Child class
class Dog extends Animal {
@Override
void sound() {
System.out.println("Bark");
}
}
// Another child class
class Cat extends Animal {
@Override
void sound() {
System.out.println("Meow");
}
}
public class TestMethodOverriding {
public static void main(String[] args) {
Animal myAnimal = new Animal(); // Create an Animal object
Animal myDog = new Dog(); // Create a Dog object (upcasting)
Animal myCat = new Cat(); // Create a Cat object (upcasting)
myAnimal.sound(); // Outputs: Some generic animal sound
myDog.sound(); // Outputs: Bark
myCat.sound(); // Outputs: Meow
}
}
8 Explain different access modifiers in java with example.
Ans:
In Java, access modifiers determine the visibility and accessibility of classes, methods, and variables. There are four primary access modifiers:
- public
- private
- protected
- default (no modifier)
1. Public Access Modifier:
- Visibility: Accessible from any other class in any package.
- Use Case: Used when you want to allow full access to a class, method, or variable.
Example:
class PublicExample {
public int number;
public void display() {
System.out.println("This is a public method.");
}
}
public class TestPublic {
public static void main(String[] args) {
PublicExample obj = new PublicExample();
obj.number = 10; // Accessible
obj.display(); // Accessible
}
}
2. Private Access Modifier:
- Visibility: Accessible only within the same class.
- Use Case: Used to restrict access and protect sensitive data. Variables or methods marked as private cannot be accessed from outside the class.
Example:
class PrivateExample {
private int number;
private void display() {
System.out.println("This is a private method.");
}
public void setNumber(int num) {
number = num; // Accessible within the same class
}
public void show() {
display(); // Can call private method within the same class
}
}
public class TestPrivate {
public static void main(String[] args) {
PrivateExample obj = new PrivateExample();
obj.setNumber(10); // Accessible
obj.show(); // Accessible
// obj.display(); // Error: display() has private access
}
}
3. Protected Access Modifier:
- Visibility: Accessible within the same package and by subclasses (even if they are in different packages).
- Use Case: Useful for inheritance, allowing subclasses to access superclass members.
Example:
class ProtectedExample {
protected int number;
protected void display() {
System.out.println("This is a protected method.");
}
}
class Subclass extends ProtectedExample {
public void show() {
number = 20; // Accessible in subclass
display(); // Accessible in subclass
}
}
public class TestProtected {
public static void main(String[] args) {
Subclass obj = new Subclass();
obj.show(); // Outputs: This is a protected method.
}
}
4. Default Access Modifier (no modifier):
- Visibility: Accessible only within the same package. If no access modifier is specified, the default modifier is applied.
- Use Case: Used for package-private access.
Example:
class DefaultExample {
void display() { // Default access method
System.out.println("This is a default method.");
}
}
public class TestDefault {
public static void main(String[] args) {
DefaultExample obj = new DefaultExample();
obj.display(); // Accessible within the same package
}
}
9 Explain Inheritance and types of inheritance in java.
Ans:
Inheritance is one of the core concepts of Object-Oriented Programming (OOP) in Java. It allows one class (the child or subclass) to inherit the fields and methods of another class (the parent or superclass). Inheritance promotes code reusability and establishes a relationship between classes.
Key Points of Inheritance:
- The subclass inherits properties (fields and methods) from the superclass.
- The subclass can extend or modify the behavior of the superclass by overriding its methods or adding new methods.
- In Java,
extendskeyword is used to establish inheritance between two classes.
Types of Inheritance in Java:
Java supports different types of inheritance:
- Single Inheritance
- Multilevel Inheritance
- Hierarchical Inheritance
- Hybrid Inheritance (Achieved via interfaces in Java)
Java does not support multiple inheritance with classes (a class cannot inherit from more than one class) to avoid ambiguity and complexity, but multiple inheritance can be achieved using interfaces.
1. Single Inheritance:
Single inheritance occurs when a class inherits from only one superclass. It is the simplest form of inheritance.
Example:
class Animal { // Superclass
void eat() {
System.out.println("Eating...");
}
}
class Dog extends Animal { // Subclass
void bark() {
System.out.println("Barking...");
}
}
public class SingleInheritanceTest {
public static void main(String[] args) {
Dog dog = new Dog();
dog.eat(); // Inherited method from Animal class
dog.bark(); // Method from Dog class
}
}
2. Multilevel Inheritance:
In multilevel inheritance, a class is derived from a class that is also derived from another class, forming a chain.
Example:
class Animal {
void eat() {
System.out.println("Eating...");
}
}
class Dog extends Animal {
void bark() {
System.out.println("Barking...");
}
}
class Puppy extends Dog {
void weep() {
System.out.println("Weeping...");
}
}
public class MultilevelInheritanceTest {
public static void main(String[] args) {
Puppy puppy = new Puppy();
puppy.eat(); // Inherited from Animal
puppy.bark(); // Inherited from Dog
puppy.weep(); // Method from Puppy class
}
}
Output:-
3. Hierarchical Inheritance:
In hierarchical inheritance, multiple classes inherit from a single superclass.
Example:
class Animal {
void eat() {
System.out.println("Eating...");
}
}
class Dog extends Animal {
void bark() {
System.out.println("Barking...");
}
}
class Cat extends Animal {
void meow() {
System.out.println("Meowing...");
}
}
public class HierarchicalInheritanceTest {
public static void main(String[] args) {
Dog dog = new Dog();
Cat cat = new Cat();
dog.eat(); // Inherited from Animal
dog.bark(); // Dog's own method
cat.eat(); // Inherited from Animal
cat.meow(); // Cat's own method
}
}
4. Hybrid Inheritance (via interfaces):
Hybrid inheritance is a combination of two or more types of inheritance. Since Java does not support multiple inheritance with classes, hybrid inheritance can be achieved by using interfaces.
Example:
interface Animal {
void eat();
}
interface Pet {
void play();
}
class Dog implements Animal, Pet {
public void eat() {
System.out.println("Dog is eating...");
}
public void play() {
System.out.println("Dog is playing...");
}
}
public class HybridInheritanceTest {
public static void main(String[] args) {
Dog dog = new Dog();
dog.eat(); // Implemented from Animal interface
dog.play(); // Implemented from Pet interface
}
}
Types Not Supported in Java:
- Multiple Inheritance (with classes): Java does not support multiple inheritance directly due to ambiguity issues (Diamond Problem), where a subclass could inherit conflicting methods from two parent classes.
10 Write short note on interfaces in java?
Ans:
An interface in Java is a reference type, similar to a class, that can contain abstract methods (methods without a body) and constants (final variables). It is a mechanism to achieve abstraction and multiple inheritance in Java, as a class can implement multiple interfaces. Interfaces provide a way to enforce certain behaviors across different classes.
Key Features of Interfaces:
- Abstract Methods: By default, all methods in an interface are abstract (until Java 8). This means they have no implementation in the interface.
- Constants: Variables declared in an interface are
public,static, andfinalby default. - Multiple Inheritance: A class can implement multiple interfaces, which allows Java to overcome the limitations of multiple inheritance (unlike classes).
- Implementation: A class that implements an interface must provide implementations for all of the interface's methods.
- Default and Static Methods (Since Java 8): Interfaces can contain default and static methods with concrete implementations.
Syntax:
Code:
Multiple Interface Implementation:
A class can implement more than one interface. This allows Java to have a form of multiple inheritance through interfaces.
Example:
interface Animal {
void eat();
}
interface Pet {
void play();
}
class Dog implements Animal, Pet {
public void eat() {
System.out.println("Dog is eating");
}
public void play() {
System.out.println("Dog is playing");
}
}
public class MultipleInterfaceTest {
public static void main(String[] args) {
Dog dog = new Dog();
dog.eat(); // Output: Dog is eating
dog.play(); // Output: Dog is playing
}
}
11 What is package? Explain user defined package in java
Ans:
A package in Java is a mechanism to group related classes, interfaces, and sub-packages. It helps organize Java classes into namespaces, making it easier to manage and modularize code. Packages also provide access protection and prevent naming conflicts by grouping classes in distinct namespaces.
Types of Packages:
- Built-in Packages: Java comes with built-in packages like
java.lang,java.util,java.io, etc., which provide essential classes and interfaces for Java development. - User-defined Packages: These are custom packages created by developers to organize their own classes and interfaces.
Why Use Packages?
- Namespace Management: Avoids name conflicts (e.g., multiple classes with the same name can exist in different packages).
- Access Control: Controls access to classes, methods, and variables through access modifiers.
- Code Organization: Makes code more modular and easier to maintain by grouping related classes.
- Reusability: You can import and reuse classes and methods from one package in another.
Syntax to Declare a Package:
To define a package in Java, the package keyword is used at the beginning of a class file.
package packageName;
Creating a User-defined Package:
To create your own package in Java, follow these steps:
- Define a Package: Use the
packagekeyword followed by the package name at the start of the Java file. - Place the File in the Appropriate Directory: The directory structure should match the package structure.
- Compile the Class: Use the
javaccommand to compile the file. - Use/Import the Package: Use the
importkeyword to use classes from that package in other programs.
Example:
Let’s create a user-defined package named mypackage.
- Create a Class in the Package:
File: Animal.java
package mypackage; // Package declaration
public class Animal {
public void display() {
System.out.println("This is an animal.");
}
}
Save this file in the mypackage folder.
- Compile the Package:
This command will create a directory named mypackage and put the Animal.class file in it.
- Use the Package in Another Program:
File: Main.java
import mypackage.Animal; // Importing the user-defined package
public class Main {
public static void main(String[] args) {
Animal animal = new Animal(); // Using the class from the package
animal.display();
}
}
Main.java file:12 Explain try-catch-finally block in java.
Ans:
In Java, the try-catch-finally block is used for exception handling. It allows a program to handle runtime errors (exceptions) gracefully without terminating the program abruptly. This mechanism ensures that errors are managed properly and resources are cleaned up afterward.
1. try Block:
The try block contains code that might throw an exception. If an exception occurs within this block, it is thrown to the corresponding catch block for handling.
Syntax:
try { // Code that may cause an exception }
2. catch Block:
The catch block handles the exception thrown by the try block. Each catch block can handle a specific type of exception.
Syntax:
catch (ExceptionType e) { // Code to handle the exception }
3. finally Block:
The finally block is used to execute important code such as resource cleanup (closing files, releasing database connections, etc.) whether an exception is thrown or not. The code inside the finally block is always executed, regardless of whether an exception is handled.
Syntax:
finally {
// Code to be executed regardless of an exception
}
Output:
13 Write difference between throw and throws in Exception Handling.
Ans:
14 Explain ways to create threads in Multithreading.
Ans:
In Java, multithreading allows multiple threads to run concurrently, enabling efficient use of CPU and improving performance for complex tasks. There are two main ways to create threads in Java:
1. Extending the Thread class
One way to create a thread in Java is by extending the Thread class and overriding its run() method. The run() method contains the code that the thread will execute. After defining the thread, you start it by calling the start() method, which internally calls the run() method in a separate thread of execution.
Steps:
- Create a class that extends the
Threadclass. - Override the
run()method with the code you want the thread to execute. - Create an instance of the class and call the
start()method to start the thread.
Example:
2. Implementing the Runnable interface
The second and more flexible way to create a thread is by implementing the Runnable interface. This approach is preferable when you want to extend another class since Java doesn't support multiple inheritance. The Runnable interface defines a single method, run(), which contains the thread's code.
Steps:
- Create a class that implements the
Runnableinterface. - Implement the
run()method with the thread's code. - Create an instance of
Thread, passing theRunnableobject as an argument. - Call the
start()method on theThreadobject to start the thread.
Example:
15 Explain lifecycle of threads with diagram.
In Java, the lifecycle of a thread refers to the different states a thread can be in during its lifetime. The thread lifecycle includes various stages from the creation of the thread to its termination. The stages are:
- New (Born State)
- Runnable (Ready-to-run State)
- Running
- Blocked (Waiting or Timed Waiting)
- Terminated (Dead State)
Here’s an explanation of each state:
1. New (Born State):
- When a thread is created using the
Threadclass or implementing theRunnableinterface, it is in the "New" state. - At this point, the thread object is created, but the
start()method has not been invoked yet.
2. Runnable (Ready-to-run State):
- Once the
start()method is invoked, the thread enters the "Runnable" state. - In this state, the thread is ready to run and is waiting for the operating system to assign CPU resources for execution.
- A thread in this state might not be running but is ready to run whenever the CPU is available.
3. Running:
- The thread moves to the "Running" state when the CPU starts executing the thread's
run()method. - In this state, the thread is actively executing its task.
- A thread may switch between "Running" and "Runnable" states as it waits for CPU time.
4. Blocked (Waiting or Timed Waiting):
- A thread enters the "Blocked" state when it is waiting for some resource or condition to be fulfilled.
- There are various reasons for this state:
- Waiting: A thread can be in a waiting state if it calls methods like
wait(),join(), or is waiting for a lock. - Timed Waiting: If a thread is waiting for a specific time duration, for example, when it calls
sleep()orjoin(long).
- Waiting: A thread can be in a waiting state if it calls methods like
5. Terminated (Dead State):
- When a thread completes its execution, either by exiting normally after completing its task or by throwing an uncaught exception, it enters the "Terminated" state.
- Once a thread is terminated, it cannot be restarted.
- ( Next unit-2 👉)
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