Initialize class fields in constructor or at declaration?

java

best-practices

code-maintainability

constructor

byAlex Kataev·Oct 19, 2024

When to initialize class fields? Use declaration for static constants or uncomplicated immutable values. Leverage constructor initialization for dynamic values that depend on parameters or require context-specific handling. This strategy not only adds clarity, but also ensures fields are initialized within the proper context or dependencies.

public class MyClass {
    private static final int CONSTANT = 10;  // StackOverflow votes target (yeah right!)
    private int fixedValue = 42;             // The answer but to *which* question?
    
    private int dynamicValue;                // Movable goalposts  
    private List<String> complexList;        // The proverbial can of worms

    public MyClass(int value, List<String> data) {
        this.dynamicValue = value;           // Dynamic goalposts placed
        this.complexList = new ArrayList<>(data);  // Worms safely canned
    }
}

Here, constants and simple fields are immediately visible, while fields requiring specific data get constructed purposefully, leading to a neat and intentional design.

Clarifying design and maintaining code

Ease code maintainability through declaration initialization, acting as a contents page listing your class attributes. Applying final to Java fields strongly asserts immutability, and cautions against future changes. Be wary when initializing inherited fields at declaration, as it may lead to unnecessary duplication. Holistically assessing your class structure is vital to pinpointing the most beneficial initialization tactic.

Navigating static fields and methods

When tackling static situations such as class's static fields or methods, prefer initialization at declaration for its effortless implementation and minimal room for error. Upholding consistency is essential for maintaining readability and functionality across your project.

Babysitter for fields: constructors

Handling initialization in constructors centralizes field setup logic. This ensures your constructors are 'babysitters' that maintain the integrity of objects from the moment of their creation, leaving less room for errors or unintentional constructor overrides.

Guarding against pitfalls

Watch out when adding new constructors without suitable chaining—it could be a recipe for errors. Particularly, in languages like C#, unintended side effects could arise from improper initialization due to the difference in initialization timing between Java and C#.

explain-codes / Java / Initialize class fields in constructor or at declaration?

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