Java Variable Initialization: Inside or Outside the Constructor?

Variable Initialization: Within or Outside the Constructor

When initializing variables in Java, developers can choose between declaring and initializing variables within the constructor (style 1) or directly within the variable declaration (style 2). Both approaches have their merits, but for readability and maintainability, style 2 is generally recommended.

Style 2: Initialization Within Variable Declaration

public class ME {
    private int i = 100;
}

Benefits of Style 2:

• Clear initialization: The default value of the variable is immediately visible upon declaration.
• Constructor conciseness: The constructor remains focused on initializing complex objects or setting dynamic values, avoiding repetitive variable initialization.
• Cross-constructor consistency: Variables are initialized with the same default value regardless of which constructor is invoked.

Style 1: Initialization Within Constructor

public class ME {
    private int i;

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

Drawbacks of Style 1:

• Split initialization: One must reference the constructor to find the variable's default value.
• Constructor repetition: If multiple constructors exist, the initialization must be repeated, which can lead to errors.
• Potential for forgetting initialization: If a constructor omits the initialization, the variable may remain uninitialized.

Conclusion

While both initialization styles are valid, style 2 is generally preferred due to its clarity, constructor conciseness, and cross-constructor consistency. It allows for easier understanding of variable values and reduces the likelihood of initialization errors.

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