1. Common operations
@Test public void test1() { F f = new F(); // of(非null对象) Optional<F> fOptional = Optional.of(f); System.out.println(fOptional); F = null ; // ofNullable (may be null objects) Optional The <F.> fOptional1 = Optional.ofNullable (F); System.out.println(fOptional1); // orElse (T T), if the package Optional entity is not empty, the object returns Optional packaging, otherwise T F. FOptional1.orElse F1 = ( new new F. ( "ADMIN" )); System.out.println(f1); // T GET (): if the object contains the value of the call, the return value, otherwise throw an exception // T orElse (T OTHER): If there is a value, the return value, otherwise return OTHER // ? T orElseGet (Supplier <Extend T> other): If there is a value returns that value, otherwise it returns OTHER // T orElseThrow (Supplier <Extend the X-> exceptionSupplier):? has a value returns that value, otherwise throw an exception }