Streamline Java Object Initialization with Inline Blocks (Including Public Fields)

When creating objects in Java, balancing simplicity, maintainability, and flexibility can be challenging. Developers often resort to techniques like constructors, the Builder pattern, or factory methods. While effective, these approaches can add unnecessary complexity for simple, one-off objects.

Enter inline initialization blocks, a concise way to initialize both private fields (via setters) and public fields directly within the object creation context. In this blog, we’ll explore how to use this technique effectively, even when public fields are involved.

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What Are Inline Initialization Blocks?

Inline initialization blocks in Java use double curly braces ({{ }}) to configure an object immediately after instantiation. This approach simplifies object setup without requiring additional constructors or boilerplate code. Here’s an example:

Updated Code with Public Fields

public class SampleInlineInitialization {

  public static void main(String[] args) {
    Person person = new Person() {{
      setName("John Smith");
      setAge(25);
      setGender("Male");
      setAddress("123 Main St.");
      setEmail(getName() + "@gmail.com");
      // Public fields
      city = "San Francisco";
      state = "CA";
    }};

    System.out.println(person);
  }

  public static class Person {
    private String name;
    private int age;
    private String gender;
    private String address;
    private String email;
    public String city;
    public String state;

    @Override
    public String toString() {
      return new StringBuilder()
              .append("{")
              .append("\"age\": ").append(this.getAge())
              .append(", \"name\": ").append(this.getName())
              .append(", \"gender\": ").append(this.getGender())
              .append(", \"address\": ").append(this.getAddress())
              .append(", \"email\": ").append(this.getEmail())
              .append(", \"city\": ").append(this.city)
              .append(", \"state\": ").append(this.state)
              .append("}").toString();
    }

    // Getters and setters
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public String getGender() { return gender; }
    public void setGender(String gender) { this.gender = gender; }
    public String getAddress() { return address; }
    public void setAddress(String address) { this.address = address; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
  }
}

Output:

{"age": 25, "name": John Smith, "gender": Male, "address": 123 Main St., "email": John [e-mail], "city": San Francisco, "state": CA}

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Why Use Inline Initialization Blocks for Public Fields?

1. Flexibility for Public Fields

Inline initialization supports direct assignment to public fields without requiring a setter. For example:

city = "San Francisco";
state = "CA";

This keeps your code simple and avoids the need to define unnecessary setter methods for public fields.

2. Localized Configuration

All field assignments—whether private or public—are conveniently located within the object instantiation block. This improves readability and maintainability by keeping the configuration logic in one place.

3. Combines the Best of Both Worlds

Inline initialization allows you to:

• Use setters for encapsulated private fields.
• Assign public fields directly.

This dual capability makes it versatile for various scenarios.

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Advantages of Using Inline Initialization Blocks

Eliminates Constructor Overloading

Instead of writing multiple constructors to handle various field combinations, you can configure fields dynamically at the point of object creation:

Person person = new Person() {{
  setName("John Smith");
  setAge(25);
  city = "San Francisco";
  state = "CA";
}};

Improves Readability

By centralizing the object setup, inline initialization eliminates confusion about where and how fields are being assigned.

Reduces Boilerplate Code

Say goodbye to redundant constructors and setters for every field. You can keep your class definition focused and clean.

Perfect for Prototyping

Inline initialization is ideal for quick prototyping, testing, or creating objects with one-off configurations.

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When to Use Inline Initialization for Public Fields

While inline initialization is convenient, it’s best suited for:

• Prototyping and Testing: Quickly set up objects without adding unnecessary methods.
• One-Off Configurations: Perfect for use cases where the object won’t need complex or reusable initialization logic.
• Lightweight Use Cases: Works well for small, simple objects where you want to minimize setup code.

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Considerations for Public Fields

Use Public Fields with Caution

While public fields are straightforward, they may expose the class to unintentional misuse. Encapsulation via private fields and setters is generally safer for production code.

Debugging Anonymous Classes

Inline initialization creates an anonymous subclass of the target class. While this rarely affects runtime behavior, debugging tools may display the subclass name instead of the original class name, which could be confusing in large projects.

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Wrapping Up

Inline initialization blocks are a powerful way to simplify object creation in Java. By supporting both private and public field assignments, they strike a balance between flexibility and simplicity.

This approach eliminates the need for overloaded constructors, enhances readability, and reduces boilerplate code. Whether you’re prototyping, testing, or creating lightweight objects, inline initialization can save you time and effort while keeping your code clean and maintainable.