LambdaExample.java

package org.athenian._3_lambdas;

public class LambdaExample {

    static void apply(String text, TextConverter... converters) {
        System.out.printf("Applying %d converters to [%s]%n", converters.length, text);
        String result = text;
        for (TextConverter converter : converters) {
            result = converter.convert(result);
            System.out.printf("Applied converter [%s] and got [%s]%n", converter.getClass().getSimpleName(), result);
        }
        System.out.println(result);
        System.out.println();
    }

    public static void main(String[] args) {
        // Anonymous class
        TextConverter toLower =
                new TextConverter() {
                    @Override
                    public String convert(String text) {
                        return text.toLowerCase();
                    }
                };

        // Convert to lambda
        TextConverter toUpper = (String text) -> {
            return text.toUpperCase();
        };

        // Simplify to expression body
        TextConverter doubler = text -> text + text;

        // Non-lambda blocks requires curlies
        TextConverter reverser = text -> {
            var sb = new StringBuilder();
            for (int i = text.length() - 1; i >= 0; i--)
                sb.append(text.charAt(i));
            return sb.toString();
        };

        apply("Hello 1", toLower);
        apply("Hello 2", toUpper);
        apply("Hello 3", doubler);
        apply("Hello 4", reverser);
        apply("Hello 5", toLower, doubler, reverser);
        apply("Hello 7", toUpper, reverser, doubler, reverser);

        apply("Hello 8", text -> text.toLowerCase());
        apply("Hello 9", text -> text.replaceAll("9", "999"));

        apply("Hello 10",
              text -> text.toUpperCase(),
              text -> text + text,
              text -> {
                  StringBuilder sb = new StringBuilder();
                  for (int i = text.length() - 1; i >= 0; i--)
                      sb.append(text.charAt(i));
                  return sb.toString();
              });
    }


    @FunctionalInterface
    public interface TextConverter {
        String convert(String text);
    }
}