Pass through the blog (https://blog.csdn.net/cxh6863/article/details/102634781), based on the use of the Stream, we should no longer strange to stream Stream, Stream will then learn advanced usage under the bar.
A packet summing -collect
Scenes:
In a class, everyone has their own score, how to use the code in java to score all based on gender, and then summed.
method:
The method used to collect collected list into the map, and then classified using groupby,
GetSum () - Get and
getMax () - Get maximum
getMin () - Get minimum
getAverage () - Get average
getCount () - Gets the amount of data
use:
System.out.println("分组求和：");
Map<String, IntSummaryStatistics> collectGroupBySex = students.stream().collect(Collectors.groupingBy(student::getSex, Collectors.summarizingInt(student::getScore)));
System.out.println("男生："+collectGroupBySex.get("男"));
System.out.println("男生的分数和："+collectGroupBySex.get("男").getSum());
System.out.println("男生中最大分数："+collectGroupBySex.get("男").getMax());
System.out.println("男生中最小分数："+collectGroupBySex.get("男").getMin());
System.out.println("男生中平均分数："+collectGroupBySex.get("男").getAverage());
System.out.println("男生个数："+collectGroupBySex.get("男").getCount());
operation result
Second, the combination of the sort -comparing-> thenComparing
Scenes:
In a class, everyone has their own score, how to use the code for all of the first fraction and then sorted according to gender sorted by score in java.
method:
comparing，thenComparing
use
System.out.println("组合排序：");
System.out.println("第一种：");
List<student> collectSortedMore = students.stream().sorted(Comparator.comparing(student::getSex).reversed().thenComparing(student::getScore).reversed()).collect(Collectors.toList());
collectSortedMore.stream().forEach(System.out::println);
System.out.println("第二种：");
students.sort(Comparator.comparing(student::getSex).reversed().thenComparing(student::getScore).reversed());
students.stream().forEach(student -> System.out.println(student));
operation result
Third, seeking extreme value -summarizingLong / summarizingInt
Scenes:
In a class, everyone has their own score, how to use the code in java average seek this class, maximum points and minimum points.
method:
First use summarizingLong and summarizingInt to score summary, then get extreme value respectivelyObtaining an average value --getAverage ()
Get the maximum --getMax ()
Gets the minimum --getMin ()
Get out --getSum ()
Get the number of --getCount ()
use
System.out.println("求极值：");
LongSummaryStatistics collectStudentsSummary = students.stream().collect(Collectors.summarizingLong(student::getScore));
System.out.println("平均值=" + collectStudentsSummary.getAverage());
System.out.println("个数=" + collectStudentsSummary.getCount());
System.out.println("最大值=" + collectStudentsSummary.getMax());
System.out.println("最小值=" + collectStudentsSummary.getMin());
System.out.println("总和=" + collectStudentsSummary.getSum());
operation result
Finally on stream and for, the following is a personal understanding:
stream and for comparison loop
for loop is a cycle of operation in order to perform
stream is carried out on one asynchronous operation
that is to say for this one operation cycle is over, then the next this operation is performed once
while the stream is almost at the same time all operations
such as the need for an operation cycle ten times, for a time loop is executed, executed 10 times, 10 times a stream is simultaneously executed 10 times.