package prepare1; class Book{ } public class Test { public static void main(String[] args) { Object obj = new Object(); Object obj1 = new Book();//向上转型 Object obj2 = "字符串";//向上转型 Book bk = (Book)obj;//向下转型 String str = (String)obj2;//向下转型 } }
package prepare1; class Book{ } public class Test { public static void main(String[] args) { Object obj = new Object(); Object obj1 = new Book();//向上转型 Object obj2 = "字符串";//向上转型 Book bk = (Book)obj;//向下转型 String str = (String)obj2;//向下转型 } }