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This article shows you how to use Stream API in Java8. The content is concise and easy to understand. It will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

First create an object

Public class Employee {private int id; private String name; private int age; private double salary; private Status status; public enum Status {FREE, BUSY, VOCATION;} public Employee () {} public Employee (String name) {this.name = name;} public Employee (String name, int age) {this.name = name; this.age = age;} public Employee (int id, String name, int age, double salary) {this.id = id This.name = name; this.age = age; this.salary = salary;} public Employee (int id, String name, int age, double salary, Status status) {this.id = id; this.name = name; this.age = age; this.salary = salary; this.status = status;} / / omit get,set and so on. }

Initialize some data casually

List empList = Arrays.asList (new Employee, "Li Si", 59, 6666.66, Status.BUSY), new Employee (101,101, "Zhang San", 18, 9999.99, Status.FREE), new Employee (6666.66, "Wang Wu", 28, 3333.33, Status.VOCATION), new Employee (104,104, "Zhao Liu", 8, 7777.77, Status.BUSY), new Employee (104, "Zhao Liu", 8, 7777.77, Status.FREE), new Employee Zhao Liu, 8, 7777.77, Status.FREE), new Employee (105, Tian Qi, 38, 5555.55, Status.BUSY))

Intermediate operation

Filter filter based on condition

/ * receives the Lambda and excludes some elements from the stream. , /

@ Testvoid testFilter () {empList.stream () .filter ((e)-> {return e.getSalary () > = 5000;}) .forEach (System.out::println);}

Skip the first n elements of the stream skip

/ * * skips elements and returns a stream that throws away the first n elements. * / @ Testvoid testSkip () {empList.stream () .filter ((e)-> e.getSalary () > = 5000) .skip (2) .forEach (System.out::println);}

Remove the repetitive element distinct

/ * filter to remove repeating elements * / @ Testvoid testDistinct () {empList.stream (). Distinct (). ForEach (System.out::println);} through the hashCode () and equals () of the elements generated by the stream.

Intercept the first n elements of a stream limit

/ * truncate the flow so that its elements do not exceed a given number. * / @ Testvoid testLimit () {empList.stream () .filter ((e)-> {return e.getSalary () > = 5000;}) .limit (3) .forEach (System.out::println);}

Map map

/ * takes a function as an argument, which is applied to each element and mapped to a new element * / @ Testvoid testMap () {empList.stream (). Map (e-> e.getName ()) .forEach (System.out::println); empList.stream () .map (e-> {empList.forEach (I-> {i.setName (i.getName () + "111");}); return e }) .notify (Collectors.toList ());}

Natural sort sorted

/ * generate a new stream in which * / @ Testvoid testSorted () {empList.stream (). Map (Employee::getName). Sorted (). ForEach (System.out::println);}

Custom sorting sorted (Comparator comp)

/ * generate a new stream in which * / @ Testvoid testSortedComparator () {empList.stream () .sorted ((x, y)-> {if (x.getAge () = = y.getAge ()) {return x.getName () .compareTo (y.getName ());} else {return Integer.compare (x.getAge (), y.getAge ());}}) .forEach (System.out::println);}

Final operation

Whether to match any element anyMatch

/ * check whether at least one element matches * / @ Testvoid testAnyMatch () {boolean b = empList.stream () .anyMatch ((e)-> e.getStatus () .equals (Status.BUSY)); System.out.println ("boolean is:" + b);}

Whether to match all elements allMatch

/ * check whether all elements match * / @ Testvoid testAllMatch () {boolean b = empList.stream () .allMatch ((e)-> e.getStatus () .equals (Status.BUSY)); System.out.println ("boolean is:" + b);}

Whether all elements noneMatch are not matched

/ * check whether there are no matching elements * / @ Testvoid testNoneMatch () {boolean b = empList.stream () .noneMatch ((e)-> e.getStatus () .equals (Status.BUSY)); System.out.println ("boolean is:" + b);}

Returns the first element findFirst

/ * return the first element * / @ Testvoid testFindFirst () {Optional op = empList.stream () .sorted ((E1, e2)-> Double.compare (e1.getSalary (), e2.getSalary ()) .findFirst (); if (op.isPresent ()) {System.out.println ("first employee name is:" + op.get (). GetName (). ToString ());}}

FindAny of any element in the return stream

/ * returns any element in the current stream * / @ Testvoid testFindAny () {Optional op = empList.stream (). Sorted ((E1, e2)-> Double.compare (e1.getSalary (), e2.getSalary ()) .findAny (); if (op.isPresent ()) {System.out.println ("any employee name is:" + op.get (). GetName (). ToString ());}}

Total number of return streams count

The total number of elements in the return stream * / @ Testvoid testCount () {long count = empList.stream () .filter ((e)-> e.getStatus () .equals (Status.FREE)) .count (); System.out.println ("Count is:" + count);}

The maximum max in the return stream

/ * * maximum value in the return stream * / @ Testvoid testMax () {Optional op = empList.stream () .map (Employee::getSalary) .max (Double::compare); System.out.println (op.get ());}

The minimum min in the return stream

/ * * minimum value in return stream * / @ Testvoid testMin () {Optional op2 = empList.stream () .min ((E1, e2)-> Double.compare (e1.getSalary (), e2.getSalary (); System.out.println (op2.get ());}

Reduced reduce

Reduction is to fold all the elements in the set into a single element output after a specified operation.

/ * elements in the flow can be combined repeatedly to get a value. Return T * / @ Testvoid testReduce () {Optional op = empList.stream (). Map (Employee::getSalary) .reduce (Double::sum); System.out.println (op.get ());} / * can repeatedly combine the elements in the stream to get a value and return Optional

* / @ Testvoid testReduce1 () {Optional sum = empList.stream () .map (Employee::getName) .flatMap (Java8Stream::filterCharacter) .map ((ch)-> {if (ch.equals ('six')) return 1; else return 0;}) .reduce (Integer::sum); System.out.println (sum.get ());}

Collect elements into list Collectors.toList ()

/ * collect the elements in the stream into list. * / @ Testvoid testCollectorsToList () {List list = empList.stream () .map (Employee::getName) .requests (Collectors.toList ()); list.forEach (System.out::println);}

Collect elements into set Collectors.toSet ()

/ * collect the elements in the stream into set. * / @ Testvoid testCollectorsToSet () {Set list = empList.stream () .map (Employee::getName) .requests (Collectors.toSet ()); list.forEach (System.out::println);}

Collect the elements from the stream into the newly created collection Collectors.toCollection (HashSet::new)

/ * collect the elements in the stream into the newly created collection. * / @ Testvoid testCollectorsToCollection () {HashSet hs = empList.stream () .map (Employee::getName) .requests (Collectors.toCollection (HashSet::new)); hs.forEach (System.out::println);}

Select the maximum value Collectors.maxBy () according to the comparator

/ select the maximum value according to the comparator. * / @ Testvoid testCollectorsMaxBy () {Optional max = empList.stream () .map (Employee::getSalary) .requests (Collectors.maxBy (Double::compare)); System.out.println (max.get ());}

Select the minimum value Collectors.minBy () according to the comparator

/ select the minimum value according to the comparator. * / @ Testvoid testCollectorsMinBy () {Optional max = empList.stream () .map (Employee::getSalary) .requests (Collectors.minBy (Double::compare)); System.out.println (max.get ());}

Collectors.summingDouble () summation of a field of an element in convection

/ * summation of integer attributes of elements in convection. * / @ Testvoid testCollectorsSummingDouble () {Double sum = empList.stream () .collect (Collectors.summingDouble (Employee::getSalary)); System.out.println (sum);}

Averaging a field of an element in convection Collectors.averagingDouble ()

/ * calculates the average value of the Integer attribute of the element in the flow. * / @ Testvoid testCollectorsAveragingDouble () {Double avg = empList.stream () .collect (Collectors.averagingDouble (Employee::getSalary)); System.out.println (avg);}

Grouping, group by Collectors.groupingBy similar to sql

/ * * grouping * / @ Testvoid testCollectorsGroupingBy () {Map map = empList.stream () .collect (Collectors.groupingBy (Employee::getStatus)); System.out.println (map);}

Multi-level grouping

/ * multilevel grouping * / @ Testvoid testCollectorsGroupingBy1 () {Map map = empList.stream () .elderly (Collectors.groupingBy (Employee::getStatus, Collectors.groupingBy ((e)-> {if (e.getAge () > = 60) return "old age"; else if (e.getAge () > = 35) return "middle age"; else return "adult";}) System.out.println (map);}

String concatenation Collectors.joining ()

/ * string concatenation * / @ Testvoid testCollectorsJoining () {String str = empList.stream () .map (Employee::getName) .concatenation (Collectors.joining (","-","-"); System.out.println (str);}

Public static Stream filterCharacter (String str) {List list = new ArrayList (); for (Character ch: str.toCharArray ()) {list.add (ch);} return list.stream ();}

The above is how to use Stream API in Java8. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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