按照日期对List排序

桃扇骨 2022-11-03 11:50 146阅读 0赞

## List排序 ##

ArrayList sort() 方法  
arraylist.sort(Comparator c)

看一下源码：

default void sort(Comparator<? super E> c) {
        
            Object[] a = this.toArray();
            Arrays.sort(a, (Comparator) c);
            ListIterator<E> i = this.listIterator();
            for (Object e : a) {
        
                i.next();
                i.set((E) e);
            }
        }

public int compareTo(String anotherString) {
        
            int len1 = value.length;
            int len2 = anotherString.value.length;
            int lim = Math.min(len1, len2);
            char v1[] = value;
            char v2[] = anotherString.value;
    
            int k = 0;
            while (k < lim) {
        
                char c1 = v1[k];
                char c2 = v2[k];
                if (c1 != c2) {
        
                    return c1 - c2;
                }
                k++;
            }
            return len1 - len2;
        }

conparator 方法是对String 类型的数据进行排序。

/**
         * Formats a Date into a date/time string.
         * @param date the time value to be formatted into a time string.
         * @return the formatted time string.
         */
        public final String format(Date date)
        {
        
            return format(date, new StringBuffer(),
                          DontCareFieldPosition.INSTANCE).toString();
        }

## sort()应用 ##

### 例子1： ###

Map<String,Object> eInfo = new HashMap<>();
      // 指定格式化格式
      SimpleDateFormat format1 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
      //强转为Date类型
       Date date=(Date) eInfo.get("0");
       format 方法对Date类型的数据转为String类型，存入map
       map.put("date",format1.format(date));
    	list.add(map);
    ....
    
    //排序，compareTo()方法是对String类型的数据排序
       =list.sort((Map<String,Object> m1, Map<String,Object> m2) -> m2.get("date").toString().compareTo(m1.get("date").toString()));

### 例子2 ###

List<ExamRecordQuery> list = orExamRecordMapper.selectEaxmRecordList(wrapper);
            //排序
            DateFormat format1 = new SimpleDateFormat("yyyy-MM-dd");
            list.sort((ExamRecordQuery m1, ExamRecordQuery m2) -> format1.format(m2.getDates()).compareTo(format1.format(m1.getDates())));

参考：  
[菜鸟教程][Link 1]

[Link 1]: https://www.runoob.com/java/java-arraylist-sort.html