inIf IntelliJ IDEA is showing a “can’t find symbol” error for a boolean field when using getter/setter annotations (like Lombok’s @Getter and @Setter), here are a few possible causes and solutions:—1. Check Lombok Plugin & Enable Annotation ProcessingIf you’re using Lombok, ensure the plugin is installed and annotation processing is enabled:Step 1: Install Lombok Plugin1. Open IntelliJ IDEA.2. Go to Preferences (⌘ ,) > Plugins.3. Search for Lombok and install it if not already installed.4. Restart IntelliJ.Step 2: Enable Annotation Processing1. Open Preferences (⌘ ,) > Build, Execution, Deployment > Compiler > Annotation Processors.2. Check Enable annotation processing.3. Click Apply > OK and restart IntelliJ.—2. Rebuild the ProjectSometimes IntelliJ does not recognize generated code. Try these steps:1. Invalidate Cache & RestartGo to File > Invalidate Caches / Restart > Invalidate and Restart.2. Rebuild the projectUse ⌘ F9 (Command + F9) or go to Build > Rebuild Project.—3. Check Field Naming and Lombok BehaviorLombok follows JavaBean naming conventions, which may cause issues with boolean fields.Issue: Boolean Field Starts with “is”If your field is named isActive:@Getter@Setterprivate boolean isActive;Lombok does not generate getIsActive(). Instead, it generates isActive(), which can cause issues.Solution: Rename the FieldChange it to:@Getter@Setterprivate boolean active; // Lombok will generate getActive() and setActive()—4. Check Dependencies (For Lombok Users)Ensure you have Lombok dependency in pom.xml (Maven) or build.gradle (Gradle):For Maven (pom.xml) org.projectlombok lombok 1.18.30 providedFor Gradle (build.gradle)dependencies { compileOnly ‘org.projectlombok:lombok:1.18.30’ annotationProcessor ‘org.projectlombok:lombok:1.18.30’}Then reload the project (⌘ ⇧ I in IntelliJ for Maven/Gradle).—5. Manually Define Getters/SettersIf Lombok isn’t working, manually define getters and setters:private boolean isActive;public boolean isActive() { return isActive;}public void setActive(boolean active) { this.isActive = active;}If it works manually but not with Lombok, the issue is with Lombok configuration.—Final Step: Check Compilation ErrorsRun:mvn clean compileor./gradlew clean buildIf

If IntelliJ IDEA is showing a “can’t find symbol” error for a boolean field when using getter/setter annotations (like Lombok’s @Getter and @Setter), here are a few possible causes and solutions:


1. Check Lombok Plugin & Enable Annotation Processing

If you’re using Lombok, ensure the plugin is installed and annotation processing is enabled:

Step 1: Install Lombok Plugin

  1. Open IntelliJ IDEA.
  2. Go to Preferences (⌘ ,) > Plugins.
  3. Search for Lombok and install it if not already installed.
  4. Restart IntelliJ.

Step 2: Enable Annotation Processing

  1. Open Preferences (⌘ ,) > Build, Execution, Deployment > Compiler > Annotation Processors.
  2. Check Enable annotation processing.
  3. Click Apply > OK and restart IntelliJ.

2. Rebuild the Project

Sometimes IntelliJ does not recognize generated code. Try these steps:

  1. Invalidate Cache & Restart
    • Go to File > Invalidate Caches / Restart > Invalidate and Restart.
  2. Rebuild the project
    • Use ⌘ F9 (Command + F9) or go to Build > Rebuild Project.

3. Check Field Naming and Lombok Behavior

Lombok follows JavaBean naming conventions, which may cause issues with boolean fields.

Issue: Boolean Field Starts with “is”

If your field is named isActive:

@Getter
@Setter
private boolean isActive;

Lombok does not generate getIsActive(). Instead, it generates isActive(), which can cause issues.

Solution: Rename the Field

Change it to:

@Getter
@Setter
private boolean active;  // Lombok will generate getActive() and setActive()

4. Check Dependencies (For Lombok Users)

Ensure you have Lombok dependency in pom.xml (Maven) or build.gradle (Gradle):

For Maven (pom.xml)

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.30</version>
    <scope>provided</scope>
</dependency>

For Gradle (build.gradle)

dependencies {
    compileOnly 'org.projectlombok:lombok:1.18.30'
    annotationProcessor 'org.projectlombok:lombok:1.18.30'
}

Then reload the project (⌘ ⇧ I in IntelliJ for Maven/Gradle).


5. Manually Define Getters/Setters

If Lombok isn’t working, manually define getters and setters:

private boolean isActive;

public boolean isActive() {
    return isActive;
}

public void setActive(boolean active) {
    this.isActive = active;
}

If it works manually but not with Lombok, the issue is with Lombok configuration.


Final Step: Check Compilation Errors

Run:

mvn clean compile

or

./gradlew clean build

If the error still persists, share the exact field and annotation you’re using!

interview process

45-Minute Java, Spring Boot, and React.js Profile Interview Plan

Objective:

To assess the candidate’s technical expertise, problem-solving skills, coding ability, and knowledge of Java, Spring Boot, and React.js within 45 minutes.


1. Introduction (2-3 Minutes)

  • Interviewer Introduction: Briefly introduce yourself and the company.
  • Candidate Introduction: Ask the candidate to introduce themselves, focusing on their experience in Java, Spring Boot, and React.js.
  • Agenda Overview: Explain the structure of the interview:
    • Core Java
    • Spring Boot
    • React.js
    • Practical Scenario
    • Questions & Closing

2. Core Java Questions (10 Minutes)

Focus on concepts relevant to backend development.

  1. Object-Oriented Programming:
    • Explain the principles of OOP.
    • Difference between abstract class and interface.
  2. Java Fundamentals:
    • Explain HashMap vs TreeMap.
    • What is the significance of the final keyword?
  3. Multithreading & Concurrency:
    • How do you implement multithreading in Java?
    • What is the difference between synchronized and Lock?
  4. Memory Management:
    • Explain Garbage Collection in Java.
    • How to handle memory leaks?
  5. Java 8 Features:
    • Explain the use of Streams and Optional.
    • What are functional interfaces and lambdas?

3. Spring Boot Questions (10 Minutes)

Dive into the backend framework knowledge.

  1. Framework Basics:
    • Explain Dependency Injection.
    • What is the purpose of @RestController, @Service, and @Repository annotations?
  2. Spring Boot Concepts:
    • What are the advantages of using Spring Boot?
    • How does Spring Boot manage configurations (e.g., application.properties)?
  3. APIs and Microservices:
    • Explain the difference between a monolithic and microservices architecture.
    • How do you secure REST APIs in Spring Boot?
  4. Database Integration:
    • How do you use Spring Data JPA to interact with a database?
    • What is the difference between save() and saveAndFlush() in JPA?
  5. Testing:
    • How do you write unit tests for Spring Boot applications?

4. React.js Questions (10 Minutes)

Focus on frontend development knowledge.

  1. React Basics:
    • What is the difference between functional and class components?
    • Explain the purpose of useState and useEffect hooks.
  2. Component Lifecycle:
    • What are React lifecycle methods?
    • How do you optimize React performance?
  3. State Management:
    • What is the difference between local state and global state?
    • How would you use Redux or Context API in a React app?
  4. React and APIs:
    • How do you fetch data in React?
    • Explain error handling while fetching data from an API.
  5. Advanced React:
    • What is lazy loading in React?
    • How do you handle form validation in React?

5. Practical Scenario (15 Minutes)

Ask the candidate to solve a real-world problem to assess their coding and problem-solving skills.

Backend Task (Spring Boot):

  • Write a REST API to manage a list of tasks.
    • Endpoints: Add task, update task, delete task, get all tasks.
    • Use an in-memory database (e.g., H2).
    • Bonus: Add validation for input data.

Frontend Task (React):

  • Create a React component to display a list of tasks fetched from the above API.
    • Add a button to mark a task as completed.
    • Bonus: Show a loading spinner while fetching data.

6. Questions and Closing (2-3 Minutes)

  • Allow the candidate to ask any questions about the role, team, or company.
  • Provide feedback on their performance (if possible) or let them know the next steps.

Notes for the Interviewer:

  • Time management is crucial; keep track of time for each section.
  • Focus on practical knowledge and problem-solving ability over theoretical knowledge.
  • Evaluate communication skills, as clear explanations are crucial for teamwork.

Good luck with the interview!

dynamic bindning in java

Dynamic binding is a technique used in Java to resolve method calls at runtime instead of compile-time. It is also known as late binding or dynamic method dispatch. Dynamic binding is an important aspect of runtime polymorphism in Java.

In Java, dynamic binding is achieved through method overriding. When a subclass overrides a method of its superclass, the method to be called is determined at runtime based on the actual type of the object that the reference variable refers to, rather than on the compile-time type of the reference variable.

Here’s an example to illustrate dynamic binding in Java:

public class Animal {
    public void makeSound() {
        System.out.println("The animal makes a sound");
    }
}

public class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Meow");
    }
}

public class TestDynamicBinding {
    public static void main(String[] args) {
        Animal animal = new Cat(); // create a new Cat object and assign it to the Animal reference variable
        animal.makeSound(); // output: Meow
    }
}

In this example, we have a superclass Animal with a method makeSound(), and a subclass Cat that overrides the makeSound() method. We then create a new Cat object and assign it to an Animal reference variable.

At runtime, the JVM determines that the actual type of the object that animal refers to is Cat, and thus calls the makeSound() method in the Cat class, resulting in the output “Meow”. This is an example of dynamic binding, where the method to be called is determined at runtime based on the actual type of the object, rather than on the compile-time type of the reference variable.

Dynamic binding is a powerful feature in Java that allows for flexible and extensible code. It enables polymorphism, which is one of the core principles of object-oriented programming.

runtime polymorphism in java

Runtime polymorphism in Java is achieved through method overriding. Method overriding is a technique in which a subclass provides its own implementation of a method that is already defined in its superclass.

Here’s how runtime polymorphism works in Java:

  1. First, a superclass is created with a method that is marked as public and virtual (i.e., can be overridden).
public class Animal {
    public void makeSound() {
        System.out.println("The animal makes a sound");
    }
}
  1. Next, a subclass is created that inherits from the superclass and overrides the method with its own implementation.
public class Cat extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Meow");
    }
}
  1. A third class is created to test the runtime polymorphism.
public class TestPolymorphism {
    public static void main(String[] args) {
        Animal animal = new Animal(); // create an instance of the Animal class
        animal.makeSound(); // output: The animal makes a sound

        Animal cat = new Cat(); // create an instance of the Cat class using the Animal reference
        cat.makeSound(); // output: Meow
    }
}

In the example above, we create an instance of the Animal class and call its makeSound() method, which outputs “The animal makes a sound”. We then create an instance of the Cat class using the Animal reference, and call its makeSound() method, which outputs “Meow”.

The makeSound() method is overridden in the Cat class and the cat object is of type Animal, but it refers to an instance of Cat, so when we call makeSound() on the cat object, the overridden method in the Cat class is invoked, resulting in the output “Meow”.

This is an example of runtime polymorphism in Java, where the method invoked is determined at runtime based on the actual object being referred to by the reference variable, rather than at compile-time based on the type of the reference variable.

final keyword in java

In Java, the final keyword is used to restrict the modification of a variable, method, or class. Once a variable, method, or class is declared as final, its value or implementation cannot be changed.

Here are some common uses of the final keyword in Java:

  1. Final variables:
    A final variable is a constant whose value cannot be changed once it is assigned. It can be assigned a value only once, either at the time of declaration or in a constructor. For example:
final int x = 10;
  1. Final methods:
    A final method is a method that cannot be overridden by a subclass. Once a method is declared as final in a superclass, its implementation cannot be changed in any subclass. For example:
public class Parent {
    public final void method() {
        // method code here
    }
}

public class Child extends Parent {
    // cannot override the Parent method
}
  1. Final classes:
    A final class is a class that cannot be subclassed. Once a class is declared as final, it cannot be extended by any subclass. For example:
public final class MyClass {
    // class code here
}

public class MySubclass extends MyClass {
    // error: cannot extend final class
}

In addition to the above uses, the final keyword is also used in Java to declare constants, as well as to prevent reference variables from being reassigned.

Super keyword in java

In Java, the super keyword is used to refer to the parent class or superclass of a subclass. It can be used to call the constructor, methods, and variables of the parent class.

Here are some common uses of the super keyword in Java:

  1. Call the superclass constructor:
    The super() constructor is used to call the constructor of the parent class. It should be the first statement in the constructor of the subclass, and it can be used with or without arguments. For example:
public class Parent {
    public Parent(int x) {
        // constructor code here
    }
}

public class Child extends Parent {
    public Child(int x, int y) {
        super(x); // calls the Parent constructor with argument x
        // constructor code here
    }
}
  1. Call the superclass method:
    The super keyword can also be used to call the method of the parent class with the same name. This is useful when the subclass wants to override the method but still wants to use the parent class’s implementation. For example:
public class Parent {
    public void method() {
        // method code here
    }
}

public class Child extends Parent {
    public void method() {
        super.method(); // calls the Parent method
        // additional code here
    }
}
  1. Access the parent class variable:
    The super keyword can also be used to access the variable of the parent class with the same name. This is useful when the subclass wants to use the parent class’s variable but also wants to add its own value to it. For example:
public class Parent {
    public int x = 10;
}

public class Child extends Parent {
    public int x = 20;

    public void method() {
        System.out.println(super.x + this.x); // prints 30
    }
}

In this example, the super.x refers to the x variable of the parent class, while this.x refers to the x variable of the child class.

covariant return type in java with example

Covariant return type is a feature introduced in Java 5 that allows a subclass method to return a type that is a subclass of the type returned by the superclass method. This means that the return type of the subclass method can be more specific than the return type of the superclass method.

Here is an example of covariant return type:

public class Animal {
    public Animal reproduce() {
        return new Animal();
    }
}

public class Dog extends Animal {
    @Override
    public Dog reproduce() {
        return new Dog();
    }
}

public class Main {
    public static void main(String[] args) {
        Animal animal = new Animal();
        Animal newAnimal = animal.reproduce(); // returns an Animal object

        Dog dog = new Dog();
        Dog newDog = dog.reproduce(); // returns a Dog object
        Animal anotherNewDog = dog.reproduce(); // also returns a Dog object, but can be cast to Animal
    }
}

In this example, the superclass Animal has a method reproduce() that returns an Animal object. The subclass Dog overrides the reproduce() method and returns a Dog object. This is possible because Dog is a subclass of Animal, so a Dog object can be treated as an Animal object.

The covariant return type allows us to write more specific code in the subclass without breaking the superclass contract. In other words, the subclass can return a more specific type, but it can still be used wherever the superclass is expected.

It’s important to note that covariant return type only applies to the return type of the method, and not to its parameters or access modifiers.

Method overriding in java

Method overriding is a feature in Java that allows a subclass to provide its own implementation of a method that is already defined in its superclass. The subclass method must have the same name, return type, and parameters as the superclass method.

When a method in a subclass has the same name and signature as a method in its superclass, the subclass method overrides the superclass method. The process of choosing the most specific implementation of a method at runtime is called dynamic method dispatch.

Here is an example of method overriding:

public class Animal {
    public void speak() {
        System.out.println("Animal speaks");
    }
}

public class Dog extends Animal {
    @Override
    public void speak() {
        System.out.println("Dog barks");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal animal = new Animal();
        animal.speak(); // output: Animal speaks

        Dog dog = new Dog();
        dog.speak(); // output: Dog barks

        Animal anotherDog = new Dog();
        anotherDog.speak(); // output: Dog barks
    }
}

In this example, we have a superclass Animal with a method speak(). We also have a subclass Dog that extends Animal and overrides the speak() method. When we create an instance of Dog, we can call its speak() method to get the overridden behavior.

It’s important to note that the @Override annotation is used in the subclass method to indicate that it is overriding a method in the superclass. This is not strictly necessary, but it can help prevent errors if the method signature in the superclass changes.

Method overloading in java

Method overloading is a feature in Java that allows multiple methods with the same name to be defined in a class, as long as they have different parameter types. This means that you can have two or more methods with the same name in a class, as long as they take different numbers or types of parameters.

The compiler determines which method to call based on the arguments passed in. The method with the most specific matching parameter list is called. Here’s an example:

public class Calculator {
  public int add(int x, int y) {
    return x + y;
  }

  public double add(double x, double y) {
    return x + y;
  }

  public int add(int x, int y, int z) {
    return x + y + z;
  }
}

In this example, we have three add methods with different parameter types. We can call either method, depending on the types of arguments passed in. For example, we can call add(2, 3) to invoke the first method, add(2.0, 3.0) to invoke the second method, or add(2, 3, 4) to invoke the third method.

Method overloading is useful because it allows you to create methods that perform similar tasks, but with different input parameters. It makes code more readable and easier to use, since you can use the same method name for different types of inputs. However, it’s important to use method overloading judiciously, since too many overloaded methods can make code harder to understand and maintain.

What is Polymorphism in java

Polymorphism is a fundamental concept in object-oriented programming, and it refers to the ability of an object to take on many forms. In Java, polymorphism is implemented through two mechanisms: method overloading and method overriding.

Method overloading allows multiple methods with the same name to be defined in a class, as long as they have different parameter types. The compiler determines which method to call based on the arguments passed in.

Here’s an example:

public class Calculator {
  public int add(int x, int y) {
    return x + y;
  }

  public double add(double x, double y) {
    return x + y;
  }
}

In this example, we have two add methods with different parameter types. We can call either method, depending on the types of arguments passed in.

Method overriding allows a subclass to provide its own implementation of a method that is already defined in its superclass. This allows a subclass to inherit the methods and fields of its superclass, but also to modify or extend its behavior as necessary.

Here’s an example:

public class Animal {
  public void makeSound() {
    System.out.println("The animal makes a sound");
  }
}

public class Cat extends Animal {
  @Override
  public void makeSound() {
    System.out.println("Meow");
  }
}

In this example, the Cat class extends the Animal class and overrides its makeSound method to provide its own implementation. We can call the makeSound method on a Cat object, and it will execute the Cat implementation.

Polymorphism allows us to write more generic code that can work with objects of different types, without having to know their specific implementation details. It is a powerful tool for building flexible and extensible code in Java.