Stream stream

Stream Use of streams

• Generative flow

Generate streams from data sources

• Intermediate operation

A stream can be followed by zero or more intermediate operations , The main purpose is to open the stream , Make some degree of data filtering mapping , Then return a new stream

• End operation

A stream can only have one termination operation , When this operation is performed , Stream is used ” light “ 了 , Cannot be operated on , So this must be the last operation of the flow forEach()

Stream Common ways to generate streams

Collection The collection of systems can generate streams using the default method

Map The set of systems generates streams indirectly

Arrays can be accessed through Stram Static methods of the interface of(T...vaues) Generative flow

        //Colluction aggregate 
         ArrayList<String> arrayList=new ArrayList();
        Stream stream = arrayList.stream();
        
        
        //Map aggregate 
        Map<String, Integer>  map=new HashMap<>();

        Stream<String> stream1 = map.keySet().stream();

        Stream<Integer> stream2 = map.values().stream();
        
        // Array 
        String[] arrs={"hello","java","hi"};
        Stream<String> arrs1 = Stream.of(arrs);
        
        

filter Filtering operation

        //Colluction aggregate 
        ArrayList<String> arrayList=new ArrayList();
        arrayList.add(" Xiao Ming Wang ");
        arrayList.add(" Zhang Xiaohong ");
        arrayList.add(" Li Dali ");
        arrayList.add(" Wang Ming ");

        // Start with a sheet , And the length is greater than or equal to 3
        arrayList.stream().filter((String s)->{ return  s.startsWith(" king ");}).filter((String s)->{return s.length()>=3;}).forEach(System.out::println);

 Stream In the middle operation limit&skip

limit： Take the first few elements to form a stream

skip： Skip several elements to form a stream

        //Colluction aggregate 
        ArrayList<String> arrayList=new ArrayList();
        arrayList.add(" Xiao Ming Wang ");
        arrayList.add(" Zhang Xiaohong ");
        arrayList.add(" Li Dali ");
        arrayList.add(" Wang Ming ");
        // Take the first three data and output them on the console 

        arrayList.stream().limit(3).forEach(System.out::println);
        System.out.println("--------------");
        // Skip three elements , Put the rest of the elements in the console output 

arrayList.stream().skip(3).forEach(System.out::println);

stream Flow intermediate operation concat&distinct 

concat： Merge two streams into one stream

distinct： Returns a stream consisting of different elements of the stream

        //Colluction aggregate 
        ArrayList<String> arrayList=new ArrayList();
        arrayList.add(" Xiao Ming Wang ");
        arrayList.add(" Zhang Xiaohong ");
        arrayList.add(" Li Dali ");
        arrayList.add(" Wang Ming ");

        // Take the first three to form a stream 
        Stream<String> limit = arrayList.stream().limit(3);
        // Take the last two to form a stream 
        Stream<String> skip = arrayList.stream().skip(2);
        // Merge these two stream outputs 
      //  Stream.concat(limit,skip).forEach(System.out::println);
        System.out.println("------------------");
        // Eliminate duplicate elements 
        Stream.concat(limit,skip).distinct().forEach(System.out::println);

stream Flow intermediate operation sorted&sorted(Comparator comparator) 

    public static void main(String[] args) {
        //Colluction aggregate 
        ArrayList<String> arrayList=new ArrayList();
        arrayList.add("zhangsan");
        arrayList.add("lisi");
        arrayList.add("wangwu");
        arrayList.add("zhaoliu");

        // Output the data on the console in alphabetical order 
//        arrayList.stream().sorted().forEach(System.out::println);
   //      Output the data on the console according to the string length , And when the length is the same , In natural order 
        arrayList.stream().sorted((o1,o2)->{int num1= o1.length()-o2.length();
        int num2=num1==0?o1.compareTo(o2):0;
        return num2;
        }).forEach(System.out::println);

 stream Flow intermediate operation map&mapToInt

        //map  Returns a stream consisting of the results of the elements that the given function applies to this flow 


        //mapToInt: Return to one IntStream It contains... That will be given   Function applies the element result of this flow 
        //arrayList.stream().map(Integer::parseInt).forEach(System.out::println);
        
        arrayList.stream().mapToInt(Integer::parseInt).forEach(System.out::println);

IntStream There is one of them. sum() The method of summation

        //Colluction aggregate 
        ArrayList<String> arrayList=new ArrayList();
        arrayList.add("10");
        arrayList.add("20");
        arrayList.add("30");
        arrayList.add("40");



        int sum = arrayList.stream().mapToInt(Integer::parseInt).sum();
        System.out.println(sum);

 Stream Common termination methods for streams

forEach()

count: There are several elements in the statistical set

        //Colluction aggregate 
        ArrayList<String> arrayList=new ArrayList();
        arrayList.add("10");
        arrayList.add("20");
        arrayList.add("30");
        arrayList.add("40");


        long count = arrayList.stream().count();
        System.out.println(count);