optional java code example

Example 1: check if optional is empty java

@Test
public void givenNull_whenCreatesNullable_thenCorrect() {
    String name = null;
    Optional<String> opt = Optional.ofNullable(name);
    assertFalse(opt.isPresent());
}

Example 2: instantiate optinal java 8

Person p = new Person();
Optional<Person> op = Optional.of(p);

Example 3: check if optional is empty java

String o = getOptional().orElse(null);
if (o == null) {
    return;
}

Example 4: java how to make a parameter optional

void foo(String a, Integer b) {
    //...
}

void foo(String a) {
    foo(a, 0); // here, 0 is a default value for b
}

foo("a", 2);
foo("a");

Example 5: java how to make a parameter optional

void foo(String a, Object... b) {
    Integer b1 = 0;
    String b2 = "";
    if (b.length > 0) {
      if (!(b[0] instanceof Integer)) { 
          throw new IllegalArgumentException("...");
      }
      b1 = (Integer)b[0];
    }
    if (b.length > 1) {
        if (!(b[1] instanceof String)) { 
            throw new IllegalArgumentException("...");
        }
        b2 = (String)b[1];
        //...
    }
    //...
}

foo("a");
foo("a", 1);
foo("a", 1, "b2");