Why Are My Field Values Not Initialized Correctly in My Constructor?

Why Shadowing Interferes with Field Initialization

Your class has fields named capacity and elements, which you try to initialize in the constructor. However, the values you set during construction are not reflected when querying field values. This behavior stems from a concept called shadowing.

Shadowing occurs when two variables share the same name but exist within different scopes. In your constructor, you declare local variables also named capacity and elements. These local variables take precedence over the corresponding fields within the scope of the constructor, effectively shadowing them.

public StringArray() {
    int capacity = 10; // Local variable shadows field
    String[] elements; // Local variable declaration without initializer
    elements = new String[capacity]; // Initializes local variable, not field
}

As a result, the assignment to the local capacity variable initializes that variable, not the field. Similarly, although you initialize the elements variable, its assignment does not impact the field because the local variable takes precedence. Hence, the field capacity remains at its default value (0) and elements is set to null.

To resolve this issue, remove the local variable declarations in the constructor to allow the names capacity and elements to refer to the instance variables.

public StringArray() {
    // Remove local variable declarations
    this.capacity = 10;
    this.elements = new String[capacity];
}

Alternatively, if retaining the constructor parameters is necessary, employ qualified names to explicitly reference the instance variables.

public StringArray(int capacity) {
    this.capacity = capacity; // Initializes the field using qualified name
}

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