Java record Lombok builder default value

Java record Lombok builder default value

I'd be happy to help you with that!

Java records are a new feature introduced in Java 14 (released in March 2019). They provide a way to simplify the creation of immutable data classes, making your code more readable and maintainable.

Lombok is a popular library that helps you automate the boilerplate code generation for various Java features, including records. With Lombok, you can create records without having to write repetitive get/set methods or constructors.

Now, let's talk about builders!

A builder pattern is a design pattern that provides a way to construct complex objects step-by-step. In Java, you can use the @Builder annotation from Lombok to create a fluent API for your record classes.

Here's an example of how you might use Lombok with records and builders:

@Value
public record Person(String name, int age) {
// no-arg constructor and get/set methods will be generated automatically
}
@Builder
public static class PersonBuilder {
private String name;
private int age;
public PersonBuilder setName(String name) {
this.name = name;
return this;
}
public PersonBuilder setAge(int age) {
this.age = age;
return this;
}
public Person build() {
return new Person(name, age);
}
}

In the example above, we define a Person record class with two fields: name and age. We then create a builder class for Person using Lombok's @Builder annotation. The builder provides methods to set the values of the name and age fields, as well as a build() method that returns an instance of the Person record.

By default, when you use Lombok with records, it generates a no-arg constructor and get/set methods for your record's fields. However, if you want to customize the behavior of your record or builder, you can override these defaults using various Lombok annotations.

For example, you might want to provide default values for some of your record's fields. In this case, you can use Lombok's @Builder.Default annotation on your builder class:

@Builder(defaults = @Builder.Default(name = "John"))
public static class PersonBuilder {
// ...
}

In the above example, we've specified that the default value for the name field is "John". This means that when you create a new instance of Person, it will have a name set to "John" unless you explicitly override this value using the builder's setName() method.

By providing default values and customizing your record and builder classes, you can make your code more flexible and easier to use. For example, you could add validation logic or conversion methods to your builder class:

@Builder(onInvalidInput = "Invalid input: {message}")
public static class PersonBuilder {
private String name;
private int age;
public PersonBuilder setName(String name) {
if (name == null || name.isEmpty()) {
throw new InvalidInputException("Name cannot be empty");
}
this.name = name;
return this;
}
// ...
}

In this example, we've added a validation check on the setName() method that ensures the input value is not null or empty. If an invalid input is provided, the builder will throw an exception with a helpful message.

Overall, using Lombok with Java records and builders provides a powerful way to create immutable data classes while minimizing boilerplate code. By customizing your record and builder classes, you can make your code more robust and maintainable.

How to set default value to variable in Java?

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In Java, there are several ways to set a default value to a variable, depending on the context and the type of the variable. Here are a few common approaches:

int myInt = 10; // myInt is initialized with the value 10

This approach is straightforward and works well for primitive types like integers.

public class Person {
private String name = "John";
private int age = 30;
public Person() {}
public Person(String name) {
this.name = name;
}
public Person(int age) {
this.age = age;
}
}

In this example, the Person class has two properties: name and age. The constructor takes no arguments and sets default values for both properties. You can also provide constructors that take specific types of arguments to override the default values.

public class MyClass {
private static int DEFAULT_VALUE = 10;
public MyClass() {}
}

In this example, the DEFAULT_VALUE is a static variable initialized to 10. All instances of the MyClass class will share the same value.

public class MyMath {
public int add(int a, int b) {
return a + b;
}
public int add(int a, int b, int c) {
return a + b + (c != 0 ? c : 5); // default value for c is 5
}
}

In this example, the add method with three parameters has a default value of 5 for the third parameter if it's not provided.

These are just a few examples of how you can set default values to variables in Java. The key is to understand the context and the type of variable you're working with to choose the best approach.

Do you have any follow-up questions or would you like me to elaborate on any of these approaches?