JavaExample2Kotlin.java

//Java to Kotlin Conversion Quizz samples for Java Magazine
//Example 0: Classes
public class Person{
        private final String name;
        private final int age;
        public Person(String name, int age) {
            this.name = name;
            this.age = age;
        }
        public Person(String name) {
            this.name = name;
            this.age = 0;
        }
        public int getAge() {
            return age;
        }
        public String getName() {
            return name;
        }
    }


//Example 1: Statics
public class MySingleton {
    private static final MySingleton instance = new MySingleton();
    private final int state = 42;

    private MySingleton() {}

    public static MySingleton getInstance() {
        return instance;
    }

    public int getState() {
        return state;
    }
}

//Example 2: Functions / Primitive/Object conversion hell
public static String convert(String value, Function<Character, String> converter) {
     return value.chars().boxed().map(i -> converter.apply((char) i.intValue())).collect(Collectors.joining(""));
}
convert("Welcome2Java'sPrimitive2ObjectHell", Integer::toBinaryString);

//Example 3: Nullability
File file = new File("/any/dir/somwhere");
String firstFileInParentFolder =
       file.getParentFile() != null &&
               f.getParentFile().listFiles() != null &&
               f.getParentFile().listFiles()[0] != null ?
               f.getParentFile().listFiles()[0].getName() : "unknown";


//Example 4: Extension methods
try (BufferedReader br = new BufferedReader(new FileReader("foo.txt"))) {
     String line;
       while ((line = br.readLine()) != null) {
           System.out.println(line);
       }
     } catch (IOException e) {
           e.printStackTrace();
     }


//Example 5: Collections
 Map<Character, Integer> characterCount = List.of("Count", "us", "all")
       .stream()
       .flatMap(p -> p.chars().mapToObj(c -> (char) c))
       .collect(Collectors.groupingBy(i -> i))
       .entrySet()
       .stream()
       .collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().size()));