慕课网996笔记

1.函数式接口

自定义函数接口

1. 只有一个方法只有一个方法
2. 函数式注解@FunctionInterface
3. 函数式接口的抽象方法签名: 函数描述符

可以定义一个或者多个statis方法
可以定义一个default方法
默认函数接口

2 流处理

1. 操作流程

2. 操作分类

3. 操作详解

3. 生成流的四种方式

1. 数值

 Stream<Integer> stream = Stream.of(1, 2, 34, 9, 52, 7);

2. 数组,集合

      IntStream arrStream = Arrays.stream(arr);

3. 函数

    Stream<Double> generate = Stream.generate(Math::random).limit(100L);

4. 文件

  Stream<String> lineStream = Files.lines(Paths.get("D:/test.java"));

4. 常见收集器

收集成为一个list

   List<Sku> collect = list.stream()
                .filter(sku -> sku.getTotalPrice() > 200)
                .collect(Collectors.toList());

按照条件分组

   List<Sku> collect = list.stream()
                .filter(sku -> sku.getTotalPrice() > 200)
                .collect(Collectors.toList());

  Map<Boolean, List<Sku>> map = list.stream().collect(Collectors.partitioningBy(sku -> sku.getTotalPrice() > 200));

5.资源关闭

传统关闭方式
try->catch->finally
jdk7新关闭方式
try->with->resource

import org.junit.Test;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;


public class FileCopyTest {
    String originUrl ="";
    String targetUrl ="";

    @Test
    public void copyFile() {
        // file in/out put stream
        FileInputStream originStream = null;
        FileOutputStream fileOutputStream = null;
        File file;
        try {
            originStream = new FileInputStream(originUrl);
            fileOutputStream = new FileOutputStream(targetUrl);

            int content;
            // iterator and read/out put byte
            while ((content = originStream.read()) != -1) {
                fileOutputStream.write(content);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fileOutputStream != null) {
                try {
                    fileOutputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (originStream != null) {
                try {
                    originStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Test
    public void copyFileNewTest() {
        try (
                FileInputStream inputStream = new FileInputStream(originUrl);
                FileOutputStream outputStream = new FileOutputStream(targetUrl);
        ) {
            int content;
            // iterator and read/out put byte
            while ((content = inputStream.read()) != -1) {
                outputStream.write(content);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

6 Optional空判断

    @Test
    public void optionTest() {
    		//三总定义方式
        Optional<Object> o = Optional.empty();
        Optional<Integer> integer = Optional.of(1);
        Optional<Object> optional = Optional.ofNullable(null);
        //空值操作
        boolean present = optional.isPresent();
        optional.ifPresent(System.out::println);
        Object we = optional.orElse("we");
        optional.orElseGet(() -> { return "else"; });
        optional.orElseThrow(() -> { throw new RuntimeException("引用缺失"); });
    }

7 线程池图解