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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