import java.util.ArrayList;
import java.util.List;

public class Ref {

    public static void main(String[] args) {
        StringBuilder s1 = new StringBuilder("Hello Java!");
        String s2 = s1.toString();
        List<String> lst = new ArrayList<String>();
        lst.add(s2);
        System.out.println(s1.getClass());
        System.out.println(s2.getClass());
        System.out.println(lst.getClass());
    }
}

What is the result?



A.

class java.lang.String
class java.lang.String
class java.util.ArrayList

B.

class java.lang.Object
class java.lang. Object
class java.util.Collection

C.

class java.lang.StringBuilder
class java.lang.String
class java.util.ArrayList

D.

class java.lang.StringBuilder
class java.lang.String
class java.util.List

題解

這題只是要知道「getClass」看的是變數所參考到的物件實體是屬於哪個類別即可。