Java Initializer Placement: Inside or Outside Constructors?

Initializer Placement in Java: Inside or Outside Constructors

When transitioning from C to Java, Java developers often face a decision regarding variable initialization: should it be inside or outside constructors?

Inside Constructors:

public class ME {
    private int i;

    public ME() {
        this.i = 100;
    }
}

This approach initializes the variable explicitly within the constructor. It allows for initialization values that vary between constructors.

Outside Constructors:

public class ME {
    private int i = 100;

    public ME() {
    }
}

Here, the variable is initialized directly in its declaration. This provides a default initialization that applies to all constructors.

Recommendation:

The preferred style is to initialize variables outside constructors. This offers several advantages:

1. Clarity: It makes the initialization value immediately apparent upon variable declaration, eliminating the need to search for it in the constructor.
2. Consistency: If the initialization value is the same across all constructors, it can be specified once in the declaration, reducing repetition.

Of course, if different constructors require different initialization values or calculations, then initialization should occur within the constructor. However, the outside constructor approach is generally considered more efficient and elegant for consistent default values.

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