Java8中新特性Optional、接口中默认方法和静态方法详解

public static String getName(User u) {
 Optional user = Optional.ofNullable(u);
 if (!user.isPresent())
 return "Unknown";
 return user.get().name;
}

public static String getName(User u) {
 return Optional.ofNullable(u)
     .map(user->user.name)
     .orElse("Unknown");
}

public static String getChampionName(Competition comp) throws IllegalArgumentException {
 if (comp != null) {
  CompResult result = comp.getResult();
  if (result != null) {
   User champion = result.getChampion();
   if (champion != null) {
    return champion.getName();
   }
  }
 }
 throw new IllegalArgumentException("The value of param comp isn't available.");
}

public static String getChampionName(Competition comp) throws IllegalArgumentException {
 return Optional.ofNullable(comp)
   .map(c->c.getResult())
   .map(r->r.getChampion())
   .map(u->u.getName())
   .orElseThrow(()->new IllegalArgumentException("The value of param comp isn't available."));
}

public void setName(String name) throws IllegalArgumentException {
 this.name = Optional.ofNullable(name).filter(User::isNameValid)
      .orElseThrow(()->new IllegalArgumentException("Invalid username."));
}

public interface Fun {
 default void getName(){
  System.out.println("hello world");
 }
 static void getAge(){
  System.out.println("nine");
 }
}

public class TestF {
 public void getName(){
  System.out.println("TestF");
 }
}
public interface TestInterface {
 default void getName(){
  System.out.println("hello world");
 }
}
public class Test extends TestF implements TestInterface{
 public static void main(String[] args) {
  Test t = new Test();
  t.getName();//输出的是TestF
 }
}

public interface TestInterface {
 default void getName(){
  System.err.println("hello world");
 }
}
public interface TestInterface1 {
  void getName();
}
public class Test1 implements TestInterface, TestInterface1{
 public void getName(){
  System.out.println("Tes1F");
 }
}