3. Class implementation

Parts of the class not included in its public interface belong to implementation:

• private attrbutes

• private Java methods (private C++ member functions.)

Compiler prevents users from gaining access to the class implementation.

Implementation is hidden from the user.

Java example of the interface/implementation:

public class IntSquare {
    // private attribute
    private int squareValue;

    // public interface
    public int getSquare( int value ) {
        SquareValue = calculateSquare( value );
        return squareValue;
    }

    // private implementation
    private int calculateSquare( int value ) {
        return value * value;
    }
}

Corresponding UML diagram:

If implementation changes, the interface remains the same.