OutputStream类用于写入文件。这怎么可能？ [英] OutputStream class is used for writing into files. How is it possible?

问题描述

以下代码引用自： http： //examples.javacodegeeks.com/core-java/io/fileoutputstream/java-io-fileoutputstream-example/

虽然OutputStream是一个抽象方法，在下面的代码中，OutputStream对象用于写入文件。

Although the OutputStream is an abstract method, at the below code, OutputStream object is used for writing into the file.

Files.newOutputStream（filepath））返回OutputStream。然后，out的类型是OutputStream，out引用OutputStream。

Files.newOutputStream(filepath)) returns OutputStream. Then, the type of out is OutputStream, and out references OutputStream.

当OutputStream是一个抽象类时，这怎么可能呢？

How can this be possible while OutputStream is an abstract class?

package com.javacodegeeks.core.io.outputstream;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class FileOutputStreamExample {

    private static final String OUTPUT_FILE = "C:\\Users\\nikos\\Desktop\\TestFiles\\testFile.txt";
    public static void main(String[] args) {

        String content = "Hello Java Code Geeks";

        byte[] bytes = content.getBytes();

        Path filepath = Paths.get(OUTPUT_FILE);

        try ( OutputStream out = Files.newOutputStream(filepath)) {

            out.write(bytes);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

推荐答案

仅仅因为声明的类型是 OutputStream ，这并不意味着实现不会创建的实例 OutputStream 的具体子类。你一直看到这个接口。例如：

Just because the declared type is OutputStream, that doesn't mean the implementation doesn't create an instance of a concrete subclass of OutputStream. You see this all the time with interfaces. For example:

public List<String> getList() {
    return new ArrayList<String>();
}

基本上你需要区分暴露的API（使用抽象类）和实现（可以选择使用它想要的任何子类）。

Basically you need to distinguish between the API exposed (which uses the abstract class) and the implementation (which can choose to use any subclass it wants).

所以 Files.newOutputStream 可以实现as：

public static OutputStream newOutputStream(Path path)
    throws IOException {
  return new FileOutputStream(path.toFile());
}

这篇关于OutputStream类用于写入文件。这怎么可能？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！