kevinpet

class PartitionFoos {
  void doStuff(Collection<Foo> foos) {
    final List<Bar> bars = new ArrayList<>();
    final List<Baz> bazes = new ArrayList<>(); 
    for (Foo f : foos) {
      f.match(new Visitor<Void>() {

        @Override
        public Void caseBar(Bar b) {
          bars.add(b);

kevinpet

class DefaultFooVisitor<T> implements Foo.Visitor<T> {
  T defaultValue;

  private DefaultFooVisitor(T defaultValue) {
    this.defaultValue = defaultValue;
  }

  @Override
  public T caseBar(Bar b) {
    return defaultValue;

kevinpet

abstract class Foo {
  abstract <T> T match(Visitor<T> visitor);

  interface Visitor<T> {
    T caseBar(Bar b);
    T caseBaz(Baz b);
  }

  static class Bar extends Foo {
    final int bar;

kevinpet

abstract class OoFoo {
  abstract void handle();

  static class Bar extends OoFoo {
    private int bar;

    private Bar(int bar) {
      this.bar = bar;
    }

kevinpet

abstract class BadFoo {

  static class Bar extends BadFoo {
    int bar;

    private Bar(int bar) {
      this.bar = bar;
    }

  }

kevinpet

abstract class Foo {
  abstract <T> T match(Visitor<T> visitor);

  interface Visitor<T> {
    T caseManyBar();
    T caseBar(int i);
    T caseBaz(String s);
  }

  static class Bar extends Foo {

kevinpet

enum Foo {
    case Bar(bar: Int)
    case Baz(baz: String)
}

func handle(f: Foo) -> Any {
    switch f {
    case .Bar(let bar):
        return bar
    case .Baz(let baz):

kevinpet

object patterns {
  abstract class Foo
  case class Bar(val bar: Int) extends Foo
  case class Baz(val baz: String) extends Foo

  def handle(f: Foo) =
    f match {
      case Bar(i) if (i > 10) => 10
      case Bar(i) => i
      case Baz(s) => s

kevinpet

object patterns {
  abstract class Foo
  class Bar(val bar: Int) extends Foo
  class Baz(val baz: String) extends Foo

  def handle(f: Foo) =
    f match {
      case b: Bar => b.bar
      case b: Baz => b.baz
    }

kevinpet

class Account {
  private Strategy strategy;
  private Map<String, Double> investments;

  boolean addInvestment(String symbol, double fraction, double riskiness) {
    if (strategy.isRiskAcceptable(fraction, riskiness)) {
      investments.put(symbol, fraction);
      return true;
    }
    return false;