CompleteableFuture 代碼執行返回錯誤

Question

我是 CompleteableFuture 的新手，並且在使用此代碼時遇到了一些問題。 嘗試下面的代碼時，我收到錯誤：(54, 11)

java: no suitable method found for supplyAsync(as::address_1)method java.util.concurrent.CompletableFuture.<U>supplyAsync(java.util.function.Supplier<U>) is not applicable
(cannot infer type-variable(s) U
(argument mismatch; invalid method reference method address_1 in 
class AsyncMain cannot be applied to given types required: java.lang.String found: no arguments

reason: actual and formal argument lists differ in length))
method java.util.concurrent.CompletableFuture.<U>supplyAsync(java.util.function.Supplier<U>,java.util.concurrent.Executor) is not applicable
(cannot infer type-variable(s) U
(actual and formal argument lists differ in length))

我看到錯誤消息告訴我為 CompletableFuture 調用的方法不正確，並且正在尋找存在的java.lang.String object 。 當我測試主要代碼以執行進程內函數時，我從System.out.println(contents.getClass())等簡單測試中看到返回輸出確實是一個字符串。 歡迎任何見解。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.concurrent.CompletableFuture;


public class AsyncMain {
    public String process(String output) throws IOException {
        URL address = new URL("https://api.publicapis.org/random?category=animal");
        InputStreamReader reader = null;
        try {

            reader = new InputStreamReader(address.openStream());

        } catch (IOException e) {
            e.printStackTrace();
        }
        BufferedReader buffer = new BufferedReader(reader);

        String contents = "";
        String line = "";

        while((line = buffer.readLine()) != null){

            if (line.isEmpty()) {
                break;
            }
            contents += line;
            //System.out.println(contents);

        }
        return contents;
    }

    public String address_3(String msg) throws IOException {
       return this.process(msg);

    }
    public String address_2(String msg) throws IOException {
        return this.process(msg);

    }

    public String address_1(String msg) throws IOException {
        return this.process(msg);

    }

    public static void main(String args[]) throws IOException {
        AsyncMain as = new AsyncMain();
        CompletableFuture<String> cf = new CompletableFuture<>();

        cf.supplyAsync(as::address_1).thenApply(as::address_2).thenApply(as::address_3);


    }
}

Answer 1

錯誤的原因是，在以下行中，

 cf.supplyAsync(as::address_1).thenApply(as::address_2).thenApply(as::address_3);

你調用方法 as::address_1 沒有參數，但方法 address_1 實際上需要一個 String 參數，因為你已經有了，

public String address_1(String msg) 拋出 IOException { return this.process(msg);

}

你可以通過改變來解決這個問題

 public String address_1(String msg) throws IOException {
        return this.process(msg);

    }

到

 public String address_1() throws IOException {

        return this.process("your_String_input");

    }

但由於您不使用 String 輸出參數，您可以更改代碼