java callback pattern

A simple sample callback pattern in java

String ・ CamelCase → snake_case ・ Lowercase → Uppercase Let's take the process of displaying after

When not using a callback pattern

`NoCallbackPattern.java`


public class NoCallbackPattern {
    /**
     *Snake from CamelCase_Convert to case
     */
    private String camelToSnake(String input) {
        return CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, input);
    }

    /**
     *Convert from lowercase to uppercase
     */
    private String capitalize(String input) {
        return input.toUpperCase();
    }

    /**
     *Convert and display
     */
    public void print(String input) {
        System.out.println(capitalize(camelToSnake(input)));
    }
}

`Main.java`


public class Main {
    public static void main(String[] args) {
        NoCallbackPattern noCallbackPattern = new NoCallbackPattern();
        noCallbackPattern.print("replaceString");
    }
}

When written with a callback pattern

`CallbackPattern.java`


public class CallbackPattern {
    private List<MyFilter> myFilters;

    public CallbackPattern(List<MyFilter> myFilters) {
        this.myFilters = myFilters;
    }

    public void print(String input) {
        String output = input;
        for (MyFilter myFilter : myFilters) {
            output = myFilter.replace(output);
        }
        System.out.println(output);
    }
}

`MyFilter.java`


public interface MyFilter {
    String replace(String input);
}

`CamelToSnake.java`


public class CamelToSnake implements MyFilter {
    @Override
    public String replace(String input) {
        return CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, input);
    }
}

`Capitalize.java`


public class Capitalize implements MyFilter {
    @Override
    public String replace(String input) {
        return input.toUpperCase();
    }
}

`Main.java`


public class Main {
    public static void main(String[] args) {
        List<MyFilter> filters = Arrays.asList(new CamelToSnake(), new Capitalize());
        CallbackPattern callbackPattern = new CallbackPattern(filters);
        callbackPattern.print("replaceString");
    }
}

** If you write using the callback pattern, you can see that the CallbackPattern class does not need to be modified when adding conversion processing because the print method depends only on the MyFilter interface **