In my program I'm reading integers form console many times. Every time, I need to type this line.
new Scanner(System.in).nextInt();
I'm used to C/C++ and I'm wondering if I can define something like
#define READINT Scanner(System.in).nextInt();
and then, in every place in my java program I can read form console as
int a = new READINT;
But I read form books Java does not support macros.
Someone please explain me why is it so, and can I do this in any other way.
You can but you shouldn't.
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 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.
Here's a demo:
src/Test.java
:
#define READINT (new java.util.Scanner(System.in).nextInt())
class Test {
public static void main(String[] args) {
int i = READINT;
}
}
cpp
command:
$ cpp -P src/Test.java preprocessed/Test.java
Result:
class Test {
public static void main(String[] args) {
int i = (new java.util.Scanner(System.in).nextInt());
}
}
Compile:
$ javac preprocessed/Test.java
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();
}
}
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();
}
}
(or do static import StdinUtil.STDIN;
and use STDIN.nextInt()
.)
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 #ifdef
s to filter out the "secret" parts of the solution. That way I could maintain the reference solution, and easily regenerate the code skeleton.
This post has been rewritten as an article here.
(*) 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!