着重基础之—Java 8 Comparator: How to Sort a List （List排序）

 

　　首先申明，这篇博客的内容不是我自己的知识，我是从国外网站搬来的，原因有二：1是因为大天朝对网络的封锁，想用google搜点技术知识，得先FQ。2.百度上的知识点你如果仔细琢磨的话会发现，所有的搜到的知识分俩类，一类是安装教程，一类是...。

　　

　　Java List排序是我们日常工作中用的比较频繁的，下面内容将介绍Java 8 Comparator 的用法：

　　1.字符串List 按字母顺序排列

List
     
       cities = Arrays.asList(       "Milan",       "london",       "San Francisco",       "Tokyo",       "New Delhi");System.out.println(cities);//[Milan, london, San Francisco, Tokyo, New Delhi]cities.sort(String.CASE_INSENSITIVE_ORDER);System.out.println(cities);//[london, Milan, New Delhi, San Francisco, Tokyo]cities.sort(Comparator.naturalOrder());System.out.println(cities);//[Milan, New Delhi, San Francisco, Tokyo, london]
     

　　* 这里要注意 london  小写'l'在排序过程中的细节。

 

　　2.整型数组排序

List
     
       numbers = Arrays.asList(6, 2, 1, 4, 9);System.out.println(numbers); //[6, 2, 1, 4, 9]numbers.sort(Comparator.naturalOrder());System.out.println(numbers); //[1, 2, 4, 6, 9]
     

　　

　　3.根据字符串字段排序

List
     
       movies = Arrays.asList(        new Movie("Lord of the rings"),        new Movie("Back to the future"),        new Movie("Carlito's way"),        new Movie("Pulp fiction"));movies.sort(Comparator.comparing(Movie::getTitle));movies.forEach(System.out::println);
     

　　输出将会是：

Movie{title='Back to the future'}Movie{title='Carlito's way'}Movie{title='Lord of the rings'}Movie{title='Pulp fiction'}

 

　　4.根据Double字段排序

List
     
       movies = Arrays.asList(        new Movie("Lord of the rings", 8.8),        new Movie("Back to the future", 8.5),        new Movie("Carlito's way", 7.9),        new Movie("Pulp fiction", 8.9));movies.sort(Comparator.comparingDouble(Movie::getRating)                      .reversed());movies.forEach(System.out::println);
     

 

　　5.自定义排序

List
     
       movies = Arrays.asList(        new Movie("Lord of the rings", 8.8, true),        new Movie("Back to the future", 8.5, false),        new Movie("Carlito's way", 7.9, true),        new Movie("Pulp fiction", 8.9, false));movies.sort(new Comparator
      
       () {    @Override    public int compare(Movie m1, Movie m2) {        if(m1.getStarred() == m2.getStarred()){            return 0;        }        return m1.getStarred() ? -1 : 1;     }});movies.forEach(System.out::println);
      
     

　　输出将会是：

Movie{starred=true, title='Lord of the rings', rating=8.8}Movie{starred=true, title='Carlito's way', rating=7.9}Movie{starred=false, title='Back to the future', rating=8.5}Movie{starred=false, title='Pulp fiction', rating=8.9}

　　当然，我们也可以用lambda表达式代替匿名类，如下：

movies.sort((m1, m2) -> {    if(m1.getStarred() == m2.getStarred()){        return 0;    }    return m1.getStarred() ? -1 : 1;});

　　

　　6.链式表达式排序

List
     
       movies = Arrays.asList(        new Movie("Lord of the rings", 8.8, true),        new Movie("Back to the future", 8.5, false),        new Movie("Carlito's way", 7.9, true),        new Movie("Pulp fiction", 8.9, false));movies.sort(Comparator.comparing(Movie::getStarred)                      .reversed()                      .thenComparing(Comparator.comparing(Movie::getRating)                      .reversed()));movies.forEach(System.out::println);
     

　　输出结果如下：

Movie{starred=true, title='Lord of the rings', rating=8.8}Movie{starred=true, title='Carlito's way', rating=7.9}Movie{starred=false, title='Pulp fiction', rating=8.9}Movie{starred=false, title='Back to the future', rating=8.5}

 

　　好了，就转载到这里。