java8-lambda-create.java

// ------------------------- define functional interface ------------------------------
@FunctionalInterface
interface Converter<F, T> {
    T convert(F from);
}

// ------------------------- use it in the code ---------------------------------------
//pass static method as reference
Converter<String, Integer> converter = Integer::valueOf;
Integer converted = converter.convert("123"); //convert string to Integer
System.out.println(converted);   // 123


class Something {
    String startsWith(String s) {
        return String.valueOf(s.charAt(0));
    }
}

Something something = new Something();
//pass instance method as reference
Converter<String, String> converter = something::startsWith;
String converted = converter.convert("Java"); //just print out the first character
System.out.println(converted);    // "J"