Java8 lambdas

Java8 lambdas

1. Functional References

   • Class::instanceMethod
   • Class::staticMethod
   • object::instanceMethod
     • public class User { private String name; public User(String name) { this.name = name; } public void printName() { System.out.println(name); } } public class Main { public static void main(String[] args) { User u1 = new User("AAA"); User u2 = new User("BBB"); User u3 = new User("ZZZ"); List userList = Arrays.asList(u1, u2, u3); userList.forEach(User::printName); // works userList.forEach(u1::printName); // compile error } }
   • EnclosingClass.this::method
     •     In an inner class, you can capture the this reference of an enclosing class as EnclosingClass.this::method. You can also capture super    
   • Class::new
     •  Stream stream = names.stream().map(Employee::new);  int[]::new is a constructor reference with one parameter: the length of the array. It is equivalent to the lambda expression n -> new int[n].  Employee[] buttons = stream.toArray(Employee[]::new);    

2. Interface

   • Constant Fields
     • implicit public,static, final
   • Default Methods
     • declared using Default
     • fully implemented method
   • Static methods
   • single abstract method makes interface functional

3. java.util.function

   • Predicate
     • BiPredicate<T,U> => boolean tes(T,U)
   • Consumer<T> => void accept(T)
   • Function<T,R> => R apply(T)
     • ToDoubleFunction<T> => double applyAsDouble(T)
     • DoubleFunction<R> => R apply(double)
   • Supplier<T> => T get()
   • Unary
     • UnaryOperator<T> => T apply(T)

4. Lambda Operations

   • filter()
   • map(Function<T,R>)
     • mapToLong()
     • mapToInt()
   • peek(Consumer<T>)
   • forEach()
   • count()
   • sum()
   • average()
   • min(Comparator<T>)
   • findFirst()
   • findAny()
   • anyMatch()
   • allMatch()
   • noneMatch()
   • mapToDouble()
   • max(Comparator<T>)
   • sorted(Comparator<T>)
   • Comparing(Function<T,U>)
   • reversed()
   • collect(Collector<?>)
   • java.util.stream.Collectors
     • averagingDouble(ToDoubleFunction<T>)
     • groupingBy(Function<K>)
       • Map&lt;String, Long&gt; counting = items.stream().collect( Collectors.groupingBy(Item::getName, Collectors.counting()));
     • joining()
     • partitioningBy(Predicate<T>)

5. Stream

   • Collection .stream() parallelStream()
   • Arrays.stream(Object[])
   • Stream.of(Object[])
   • intStream.range()
   • Stream.iterate(Object,UnaryOperator)
   • BufferedReader.lines()