Q001

NO.149 Which three annotation uses are valid? (Choose three.)
A. Function<String, String> func = (@NonNull x) -> x.toUpperCase();
B. var v = "Hello" + (@Interned) "World"
C. Function<String, String> func = (var @NonNull x) -> x.toUpperCase();
D. Function<String, String> func = (@NonNull var x) -> x.toUpperCase();
E. var myString = (@NonNull String) str;
F. var obj = new @Interned MyObject();


Answer: DEF

A 的 x 沒有型別，是錯誤的。標註需寫在 var 或型別之前。

ps : @NonNull 是第三方框架，比如 javax，所以無法在這課程中測試。

Q002

NO.221 Given:
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@interface AuthorInfo {
    String author() default "";
    String date();
    String[] comments() default {};
}

Which two are correct? (Choose two.)
A.
@AuthorInfo(date = "1-1-2020", comments = {null})
class Hello {
    public void func() {}
}

B.
class Hello {
    @AuthorInfo(date = "1-1-2020", comments = "Hello")
    public void func() {}
}

C.
class Hello {
    @AuthorInfo
    public void func() {}
}

D.
@AuthorInfo(date = "1-1-2020")
class Hello {
    public void func() {}
}

E.
class Hello {
    @AuthorInfo(date = "1-1-2020", author = "Gandhi", comments = "Hello")
    public void func() { }
}
A. Option A
B. Option B
C. Option C
D. Option D
E. Option E


Answer: BE

@Target(ElementType.METHOD) 標示著註解只能用在方法上。

而 date 沒有 default，所以一定要寫。