How to do string formatting with placeholders in Java (like in Python)?

Question

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?

Solution 1

The MessageFormat class looks like what you're after.

System.out.println(MessageFormat.format("{0} + {1} = {2}", x, y, x + y));

Solution 2

Java 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".

Solution 3

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.

Solution 4

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"

Solution 5

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);

View more solutions

Comments

[Ashwini Chaudhary]

This % based string formatting is similar to old-style formatting used in python, OP is using the new-style string formatting

[Rana Ghosh]

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.

[Rana Ghosh]

Thanks for the comment btw. Otherwise I wouldn't have understood why @rgettman was getting so many upvotes.

[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 brackets