建立Stream

1.建立Stream　　　　　　　　

create Stream from Collections;

create Stream from values;

create Stream from Arrays;

craeate Stream from files;

craeate Stream from functions

代碼舉例：

 1 package com.cy.java8;
 2 
 3 import java.io.IOException;
 4 import java.nio.file.Files;
 5 import java.nio.file.Path;
 6 import java.nio.file.Paths;
 7 import java.util.Arrays;
 8 import java.util.List;
 9 import java.util.stream.Stream;
10 
11 public class CreateStream {
12 
13     public static void main(String[] args) {
14         createStreamFromCollection().forEach(System.out::println);
15 
16         createStreamFromValues().forEach(System.out::println);
17 
18         createStreamFromArrays().forEach(System.out::println);
19 
20         createStreamFromFile().forEach(System.out::println);
21     }
22 
23 
24     /**
25      * create stream from collection
26      * 這裏list的元素的順序放到strem中不會改變，原來是什麼樣的順序，stream中就是什麼樣。
27      * @return
28      */
29     private static Stream<String> createStreamFromCollection(){
30         List<String> list = Arrays.asList("hello", "world", "stream");
31         return list.stream();
32     }
33 
34     private static Stream<String> createStreamFromValues(){
35         return Stream.of("hello", "world", "stream");
36     }
37 
38     private static Stream<String> createStreamFromArrays(){
39         String[] strings = new String[]{"hello", "world", "stream"};
40         return Arrays.stream(strings);
41     }
42 
43     /**
44      * create stream from file
45      * @return
46      */
47     private static Stream<String> createStreamFromFile(){
48         Path path = Paths.get("F:\\IdeaProjects\\Java8Learning\\java8\\src\\main\\java\\com\\cy\\java8\\CreateStream.java");
49         Stream<String> lines = null;
50         try {
51             lines = Files.lines(path);
52         } catch (IOException e) {
53             throw new RuntimeException(e);
54         }
55         return lines;
56     }
57 }

打印結果以下：

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

import java.io.IOException;
....
把CreateStream.java文件分行打印出來了...

2.建立Stream　　　　　　　　

create stream from Stream.iterate;

create stream from Stream.generate;

代碼例子：

 1 package com.cy.java8;
 2 
 3 import lombok.AllArgsConstructor;
 4 import lombok.Getter;
 5 import lombok.ToString;
 6 
 7 import java.util.Random;
 8 import java.util.function.Supplier;
 9 import java.util.stream.Stream;
10 
11 public class CreateStream2 {
12 
13     public static void main(String[] args) {
14         createStreamFromIterator().forEach(System.out::println);
15 
16         createStreamFromGenerate().forEach(System.out::println);
17 
18         createObjStreamFromGenerate().forEach(System.out::println);
19     }
20 
21     /**
22      * 這裏會產生一個無限的Stream
23      * 0,2,4,6,8...
24      * 能夠limit來獲取指定個數
25      * @return
26      */
27     private static Stream<Integer> createStreamFromIterator(){
28         Stream<Integer> stream = Stream.iterate(0, a -> a + 2).limit(3);
29         return stream;
30     }
31 
32     /**
33      * 也會建立一個無限的stream
34      * 相似的IntStream，DoubleStream也是相似用法
35      * @return
36      */
37     private static Stream<Double> createStreamFromGenerate(){
38         Stream<Double> stream = Stream.generate(Math::random).limit(3);
39         return stream;
40     }
41 
42     /**
43      * 自定義一個Obj的stream
44      * @return
45      */
46     private static Stream<Obj> createObjStreamFromGenerate(){
47         Stream<Obj> objStream = Stream.generate(new ObjSuppiler()).limit(3);
48         return objStream;
49     }
50 
51     static class ObjSuppiler implements Supplier<Obj>{
52         private int index = 0;
53         private Random random = new Random(System.currentTimeMillis());
54 
55         @Override
56         public Obj get() {
57             index = random.nextInt(100);
58             return new Obj(index, "Name-"+index);
59         }
60     }
61 
62     @Getter
63     @AllArgsConstructor
64     @ToString
65     static class Obj{
66         private int id;
67         private String name;
68     }
69 }

打印以下：

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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