DSL example

gistfile1.java

public class Input {

      public static MaskableInput filteredBy(Mask mask) {
        return new MaskableInput(mask);
    }

    static class MaskableInput {
        private Mask mask;

        private MaskableInput(Mask mask) {
            this.mask = mask;
        }

        public TransformableInput transformedBy(Transformation transformation) {
            return new TransformableInput(transformation);
        }

        class TransformableInput {
            private final Transformation transformation;

            private TransformableInput(Transformation transformation) {
                this.transformation = transformation;
            }

            public ValuedInput valueOf(InitialValue initialAmount) {
                return new ValuedInput(initialAmount.asText());
            }

            class ValuedInput implements Showable {
                private final String text;

                private ValuedInput(String text) {
                    this.text = text;
                }

                public ValuedInput valueOf(String text) {
                    return new ValuedInput(text);
                }

	        @Override
                public void showInto(JFormattedTextField inputField) {
                    String filteredInput = MaskableInput.this.mask.applyTo(this.text);
                    new OutputFactory().buildFrom(filteredInput).showInto(inputField);
                }

                class OutputFactory {
                    public Showable buildFrom(String input) {
                        return (input.isEmpty()) ? new FixedOutput(input) : new TransformedOutput(input);
                    }
                }

                class FixedOutput implements Showable {
                    private final String value;

                    private FixedOutput(String value) {
                        this.value = value;
                    }

		    @Override
                    public void showInto(JFormattedTextField inputField) {
                        // reset the internal value of the JFormattedTextField and just put text
                        inputField.setValue(null);
                        inputField.setText(this.value);
						
                        // clear previous results
                        TransformableInput.this.transformation.reset();
                    }
                }

                class TransformedOutput implements Showable {
                    private final String input;

                    private TransformedOutput(String input) {
                        this.input = input;
                    }

		    @Override
                    public void showInto(JFormattedTextField inputField) {
                        Object transformedInput = TransformableInput.this.transformation.from(this.input);
                        inputField.setValue(transformedInput);
                    }
                }
            }
        }
    }
}

// Initialized as:
ValuedInput input = Input.filteredBy(mask).transformedBy(transformation).valueOf(initialAmount)

// Recreated as:
input = input.valueOf(newAmmount);

// Used as:
input.showInto(formattedTextField)