Java 8 cheat sheet code

Debuggable.java

public interface Debuggable {
  default String debug() {
    StringBuilder sb = new StringBuilder(this.getClass().getName());
    sb.append(" [ ");
    Field[] fields = this.getClass().getDeclaredFields();
    for(Field f: fields) {
      f.setAccessible(true);
      try {
        sb.append(f.getName() + " = " + f.get(this));
        sb.append(", ");
      } catch (IllegalArgumentException | IllegalAccessException e) {
        throw new RuntimeException(e);
      }
    }
    sb.append("]");
    return sb.toString();
  }
} 

Lambdas1.java

// takes a Long, returns a String
Function<Long, String> f = l -> l.toString(); 

// takes nothing gives you Threads
Supplier<Thread> s =Thread::currentThread; 

// takes a string as the parameter 
Consumer<String> c = System.out::println; 

Lambdas2.java

// use them in with streams
new ArrayList<String>().stream(). 
// peek: debug streams without changes
peek(e -> System.out.println(e)). 
// map: convert every element into something  
map(e -> e.hashCode()). 
// filter: pass some elements through
filter(e -> ((e.hashCode() % 2) == 0)).   
// collect the stream into a collection 
collect(Collectors.toCollection(TreeSet::new))

Main.java

public class Main implements Debuggable {
  int a = 100;
  String b = "Home";
  
  public static void main(String[] args) {
    Main m = new Main();
    System.out.println(m.debug());
  }
}

Optional1.java

User user = getUser(name); // might return null
Location location = null;
if(user != null) { 
  location = getLocation(user);
}

Optional2.java

Optional<User> user = Optional.ofNullable(getUser(user)); 
Optional<Location> location = user.map(u -> getLocation(user));

OptionalFlatMap.java

public <U> Optional<U> flatMap(Function<? super T,Optional<U>> mapper)