問題描述

在我的程序中，我多次從控制臺讀取整數.每次，我都需要輸入這一行.

In my program I'm reading integers form console many times. Every time, I need to type this line.

new Scanner(System.in).nextInt(); 

我習慣了 C/C++，我想知道我是否可以定義類似的東西

I'm used to C/C++ and I'm wondering if I can define something like

#define READINT Scanner(System.in).nextInt(); 

然后，在我的 java 程序的每個地方，我都可以將表單控制臺讀取為

and then, in every place in my java program I can read form console as

int a = new READINT;

但是我閱讀了表格書籍 Java 不支持宏.

But I read form books Java does not support macros.

請有人解釋一下為什么會這樣，我可以用其他方式嗎?

Someone please explain me why is it so, and can I do this in any other way.

推薦答案

你可以但你不應該.

您不應該因為以這種方式使用預處理器 被認為是不好的做法，并且有更好、更符合 Java 習慣的方法來解決這個用例.

You shouldn't because using the pre-processor in that way is considered bad practice to start with, and there are better and more Java-idiomatic ways to solve this use case.

Java 本身不支持宏.另一方面，您可以通過 C 預處理器 管道源代碼a>(簡稱CPP)就像C/C++編譯鏈一樣.

Java itself doesn't support macros. On the other hand, you could pipe the source code through the C pre processor (CPP for short) just like the C/C++ compile chain does.

這是一個演示:

src/Test.java:

#define READINT (new java.util.Scanner(System.in).nextInt())

class Test {
    public static void main(String[] args) {
        int i = READINT;
    }
}

cpp 命令:

cpp command:

$ cpp -P src/Test.java preprocessed/Test.java

結果:

class Test {
    public static void main(String[] args) {
        int i = (new java.util.Scanner(System.in).nextInt());
    }
}

編譯:

$ javac preprocessed/Test.java

您可以使用靜態方法編寫自己的實用程序類:

You can write your own utility class with a static method instead:

import java.util.Scanner;
class StdinUtil {
    public final static Scanner STDIN = new Scanner(System.in);
    public static int readInt() {
        return STDIN.nextInt();
    }
}

而當你想使用它的時候，你可以靜態導入readInt方法:

And when you want to use it, you can statically import the readInt method:

import static StdinUtil.readInt; 

class Test {
    public static void main(String[] args) {
        int i = readInt();
    }
}

(或執行 static import StdinUtil.STDIN; 并使用 STDIN.nextInt().)

(or do static import StdinUtil.STDIN; and use STDIN.nextInt().)

我自己曾經對 Java 代碼使用過 CPP 預處理方法！我正在為一門課程創建一個編程作業.我希望能夠輕松地從參考解決方案中提取代碼骨架.所以我只是使用了幾個 #ifdef 來過濾掉解決方案的秘密"部分.這樣我就可以維護參考解決方案，并輕松地重新生成代碼骨架.

I myself used the CPP preprocessing approach on Java code once! I was creating a programming assignment for a course. I wanted to be able to easily extract a code skeleton out of the reference solution. So I just used a few #ifdefs to filter out the "secret" parts of the solution. That way I could maintain the reference solution, and easily regenerate the code skeleton.

這篇文章已被重寫為一篇文章這里.

This post has been rewritten as an article here.

^{(*) 因為我討厭用你不應該"來回答問題.此外，一些未來的讀者可能有充分的理由希望將 cpp 與 Java 源代碼結合使用！}

^{(*) Since I hate answering questions with "you shouldn't". Besides, some future reader may have good reasons for wanting to use the cpp in conjunction with Java sources!}

這篇關于我可以在 Java 源文件中有宏嗎的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！