创建Stream

1.创建Stream　　　　　　　　

create Stream from Collections;

create Stream from values;

create Stream from Arrays;

craeate Stream from files;

craeate Stream from functions

代码举例：

 package com.cy.java8;

 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Stream;

 public class CreateStream {

     public static void main(String[] args) {
         createStreamFromCollection().forEach(System.out::println);

         createStreamFromValues().forEach(System.out::println);

         createStreamFromArrays().forEach(System.out::println);

         createStreamFromFile().forEach(System.out::println);
     }

     /**
      * create stream from collection
      * 这里list的元素的顺序放到strem中不会改变，原来是什么样的顺序，stream中就是什么样。
      * @return
      */
     private static Stream<String> createStreamFromCollection(){
         List<String> list = Arrays.asList("hello", "world", "stream");
         return list.stream();
     }

     private static Stream<String> createStreamFromValues(){
         return Stream.of("hello", "world", "stream");
     }

     private static Stream<String> createStreamFromArrays(){
         String[] strings = new String[]{"hello", "world", "stream"};
         return Arrays.stream(strings);
     }

     /**
      * create stream from file
      * @return
      */
     private static Stream<String> createStreamFromFile(){
         Path path = Paths.get("F:\\IdeaProjects\\Java8Learning\\java8\\src\\main\\java\\com\\cy\\java8\\CreateStream.java");
         Stream<String> lines = null;
         try {
             lines = Files.lines(path);
         } catch (IOException e) {
             throw new RuntimeException(e);
         }
         return lines;
     }
 }

打印结果如下：

hello
world
stream
hello
world
stream
hello
world
stream
package com.cy.java8;

import java.io.IOException;
....
把CreateStream.java文件分行打印出来了...

2.创建Stream　　　　　　　　

create stream from Stream.iterate;

create stream from Stream.generate;

代码例子：

 package com.cy.java8;

 import lombok.AllArgsConstructor;
 import lombok.Getter;
 import lombok.ToString;

 import java.util.Random;
 import java.util.function.Supplier;
 import java.util.stream.Stream;

 public class CreateStream2 {

     public static void main(String[] args) {
         createStreamFromIterator().forEach(System.out::println);

         createStreamFromGenerate().forEach(System.out::println);

         createObjStreamFromGenerate().forEach(System.out::println);
     }

     /**
      * 这里会产生一个无限的Stream
      * 0,2,4,6,8...
      * 可以limit来获取指定个数
      * @return
      */
     private static Stream<Integer> createStreamFromIterator(){
         Stream<Integer> stream = Stream.iterate(0, a -> a + 2).limit(3);
         return stream;
     }

     /**
      * 也会创建一个无限的stream
      * 类似的IntStream，DoubleStream也是类似用法
      * @return
      */
     private static Stream<Double> createStreamFromGenerate(){
         Stream<Double> stream = Stream.generate(Math::random).limit(3);
         return stream;
     }

     /**
      * 自定义一个Obj的stream
      * @return
      */
     private static Stream<Obj> createObjStreamFromGenerate(){
         Stream<Obj> objStream = Stream.generate(new ObjSuppiler()).limit(3);
         return objStream;
     }

     static class ObjSuppiler implements Supplier<Obj>{
         private int index = 0;
         private Random random = new Random(System.currentTimeMillis());

         @Override
         public Obj get() {
             index = random.nextInt(100);
             return new Obj(index, "Name-"+index);
         }
     }

     @Getter
     @AllArgsConstructor
     @ToString
     static class Obj{
         private int id;
         private String name;
     }
 }

打印如下：

0
2
4
0.2300226452750267
0.48246633929281424
0.051774439637685465
CreateStream2.Obj(id=97, name=Name-97)
CreateStream2.Obj(id=84, name=Name-84)
CreateStream2.Obj(id=18, name=Name-18)

　　

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