[数据结构与算法]Java实现List中集合的元素进行排序

简单集合排序

    public static List<Integer> getIntegerList(){
        List<Integer> integerList = new ArrayList<>();
        integerList.add(23);
        integerList.add(15);
        integerList.add(35);
        integerList.add(68);
        integerList.add(43);
        integerList.add(8);
        return integerList;
    }

    /**
     * Integer集合排序
     */
    @Test
    public void sortIntegerList(){
        List<Integer> integerList = getIntegerList();
        System.out.println("排序前："+integerList);
        //Integer本身有实现Comparable接口
        Collections.sort(integerList);
        System.out.println("排序后："+integerList);
    }

输出：

排序前：[23, 15, 35, 68, 43, 8]
排序后：[8, 15, 23, 35, 43, 68]

根据对象集合某个字段排序

    public static List<User> getUserList(){
        List<User> userList = new ArrayList<>();
        userList.add(new User("小明",11,"北京",66));
        userList.add(new User("小红",12,"上海",99));
        userList.add(new User("小詹",14,"广州",77));
        userList.add(new User("小龙",16,"深圳",55));
        userList.add(new User("小斯",9,"迈阿密",33));
        userList.add(new User("小布",12,"伦敦",88));
        return userList;
    }

    @Test
    public void sortUserListByAge(){
        List<User> userList = getUserList();
        System.out.println("排序前："+userList);
        //如果想直接通过Collections.sort(userList)排序，需要User实现Comparable接口，并重写compareTo方法
        Collections.sort(userList, new Comparator<User>() {
            @Override
            public int compare(User o1, User o2) {
                //由小到大排序
                return o1.getAge() - o2.getAge();
                //由大到小排序
                //return o2.getAge() - o1.getAge();
            }
        });
        System.out.println("排序后："+userList);
    }

输出：

排序前：[User(name=小明, age=11, city=北京, score=66), User(name=小红, age=12, city=上海, score=99),
 User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55),
  User(name=小斯, age=9, city=迈阿密, score=33), User(name=小布, age=12, city=伦敦, score=88)]
排序后：[User(name=小斯, age=9, city=迈阿密, score=33), User(name=小明, age=11, city=北京, score=66), 
User(name=小红, age=12, city=上海, score=99), User(name=小布, age=12, city=伦敦, score=88),
User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55)]

根据对象集合多个字段排序

    @Test
    public void sortUserList(){
        List<User> userList = getUserList();
        System.out.println("排序前："+userList);
        //如果想直接通过Collections.sort(userList)排序，需要User实现Comparable接口，并重写compareTo方法
        Collections.sort(userList, new Comparator<User>() {
            @Override
            public int compare(User o1, User o2) {
                //先按照年龄排序
                int i = o1.getAge() - o2.getAge();
                if(i == 0){
                    //如果年龄相等再用分数进行排序
                    return o1.getScore() - o2.getScore();
                }
                return i;
            }
        });
        System.out.println("排序后："+userList);
    }

输出：

排序前：[User(name=小明, age=11, city=北京, score=66), User(name=小红, age=12, city=上海, score=99), 
User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55), 
User(name=小斯, age=9, city=迈阿密, score=33), User(name=小布, age=12, city=伦敦, score=88)]
排序后：[User(name=小斯, age=9, city=迈阿密, score=33), User(name=小明, age=11, city=北京, score=66),
 User(name=小布, age=12, city=伦敦, score=88), User(name=小红, age=12, city=上海, score=99), 
 User(name=小詹, age=14, city=广州, score=77), User(name=小龙, age=16, city=深圳, score=55)]