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  • java ? super E 和 ? extends E

    /**
         * 泛型固定下边界
         * ? super E  
         * 
         * 泛型固定上边界
         * ? extends E
         */
        public static void main(String[] args) {
            //demo1();
            TreeSet<Student> ts1 = new TreeSet<>(new CompareByAge());
            ts1.add(new Student("张三", 33));
            ts1.add(new Student("李四", 13));
            ts1.add(new Student("王五", 23));
            ts1.add(new Student("赵六", 43));
            
            TreeSet<BaseStudent> ts2 = new TreeSet<>(new CompareByAge());
            ts2.add(new BaseStudent("张三", 33));
            ts2.add(new BaseStudent("李四", 13));
            ts2.add(new BaseStudent("王五", 23));
            ts2.add(new BaseStudent("赵六", 43));
            
            System.out.println(ts2);
        }
    
        public static void demo1() {
            ArrayList<Student> list1 = new ArrayList<>();
            list1.add(new Student("张三", 23));
            list1.add(new Student("李四", 24));
            
            ArrayList<BaseStudent> list2 = new ArrayList<>();
            list2.add(new BaseStudent("王五", 25));
            list2.add(new BaseStudent("赵六", 26));
            
            list1.addAll(list2);
        }
    
    }
    
    class CompareByAge implements Comparator<Student> {
    
        @Override
        public int compare(Student s1, Student s2) {
            int num = s1.getAge() - s2.getAge();
            return num == 0 ? s1.getName().compareTo(s2.getName()) :  num;
        }
        
    }
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  • 原文地址:https://www.cnblogs.com/yimian/p/6537134.html
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