如何在Java中编写等效于匿名类的内容？

This is more of a generic Go question related to interfaces/functions/closures/types/..., but with a concrete use case of performing I/O.

Given an io.Reader variable I want to create an io.ReadCloser with a custom Close() implementation.

var file os.File
file = ... // some File which needs to be closed

var reader io.Reader
reader = ... // get Reader from somewhere

var readCloser io.ReadCloser
readCloser = ... // how to create a ReadCloser here?

In Java, I would write something like:

readCloser = new io.ReadCloser() {
    Read(p []byte) {
        reader.Read(p);
    }

    Close() {
        // my custom close implementation
        file.Close()
    }    
}

// now pass readCloser around as needed

How to do that with Go?

taking a hint from http.HandlerFunc , i could think of the following

package main

import (
    "bytes"
    "fmt"
    "io"
    "strings"
)

// ReadData reads data from an io.Reader
func ReadData(r io.Reader) {
    buf := new(bytes.Buffer)
    buf.ReadFrom(r)
    s := buf.String()
    fmt.Printf("read : %s 
", s)
}

// ReaderFunc takes a function and returns io.Reader
type ReaderFunc func([]byte) (int, error)

func (r ReaderFunc) Read(b []byte) (int, error) {
    return r(b)
}

func main() {
    // invoking ReadData with a regular io.Reader
    r := strings.NewReader("data 123")
    ReadData(r)

    // invoking ReadData with an anonymous io.Reader
    r = strings.NewReader("data 456")
    ReadData(ReaderFunc(func(b []byte) (int, error) {
        return r.Read(b)
    }))
}

One way could be to create your own type that combines a io.Reader and a io.Closer and implements the io.ReadCloser interface. Something like this:

type ReadCloseCombiner struct {
    io.Reader
    io.Closer
}

func (rcc ReadCloseCombiner) Read(p []byte) (n int, err error) {
    return rcc.Reader.Read(p)
}

func (rcc ReadCloseCombiner) Close() error {
    return rcc.Closer.Close()
}

And use it like this:

var file *os.File
file = ... // some File which needs to be closed

var reader io.Reader
reader = ... // get Reader from somewhere

var readCloser io.ReadCloser
readCloser = ReadCloseCombiner{reader, file}

// now pass readCloser around as needed
readCloser.Read(...)
readCloser.Close()

If you want something more flexible i would concider having a type that take a read and close function instead and then you could pass it anonymous functions (or even reader.Read/file.Close in your case).