I am new to Java and am from Python. In Python we do string formatting like this:
>>> x = 4
>>> y = 5
>>> print("{0} + {1} = {2}".format(x, y, x + y))
4 + 5 = 9
>>> print("{} {}".format(x,y))
4 5
How do I replicate the same thing in Java?
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Does this answer your question? Named placeholders in string formattingjjbskir– jjbskir2024-02-16 15:09:17 +00:00Commented Feb 16, 2024 at 15:09
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6 Answers
The MessageFormat class looks like what you're after.
System.out.println(MessageFormat.format("{0} + {1} = {2}", x, y, x + y));
2 Comments
Jesse Chisholm
With the caveat that
MessageFormat.format does not handle the empty place holder {}.
I.G. Pascual
... and the caveat that if you use
'{ it won't recognise the bracketsJava has a String.format method that works similarly to this. Here's an example of how to use it. This is the documentation reference that explains what all those % options can be.
And here's an inlined example:
package com.sandbox;
public class Sandbox {
public static void main(String[] args) {
System.out.println(String.format("It is %d oclock", 5));
}
}
This prints "It is 5 oclock".
3 Comments
Ashwini Chaudhary
This
% based string formatting is similar to old-style formatting used in python, OP is using the new-style string formatting
Daniel Kaplan
Ah, from the question I didn't know he was putting that much emphasis on using curly brackets. I thought he just wanted a way to format a string without concatenating strings and variables together.
Daniel Kaplan
Thanks for the comment btw. Otherwise I wouldn't have understood why @rgettman was getting so many upvotes.
Slf4j has MessageFormatter.format() that accepts {} without the argument number, just like Python. Slf4j is a popular logging framework, but you don't have to use it for logging to use MessageFormatter.
Comments
You can do this (using String.format):
int x = 4;
int y = 5;
String res = String.format("%d + %d = %d", x, y, x+y);
System.out.println(res); // prints "4 + 5 = 9"
res = String.format("%d %d", x, y);
System.out.println(res); // prints "4 5"
Comments
If you want to use empty placeholders (without positions), you could write a small utility around Message.format(), like this
void print(String s, Object... var2) {
int i = 0;
while(s.contains("{}")) {
s = s.replaceFirst(Pattern.quote("{}"), "{"+ i++ +"}");
}
System.out.println(MessageFormat.format(s, var2));
}
And then, can use it like,
print("{} + {} = {}", 4, 5, 4 + 5);
1 Comment
FNL
I like this approach. But I would put this into a Formatter class with a format method.
If you use Log4j 2 (log4j-api) then you can use ParameterizedMessage.
ParameterizedMessage.format("{} {}", new Object[] {x, y});
or
new ParameterizedMessage("{} {}", x, y).getFormattedMessage(); // there is trimming
