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

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，得先翻墙。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<String> 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<Integer> 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<Movie> 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<Movie> 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<Movie> 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<Movie>() {
    @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<Movie> 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。