Note that there is no variable interpolation in Java. Variable interpolation is variable substitution with its value inside a string. An example in Ruby:
#!/usr/bin/ruby
age = 34
name = "William"
puts "#{name} is #{age} years old"
The Ruby interpreter automatically replaces variables with its values inside a string. The fact, that we are going to do interpolation is hinted by sigil characters. In Ruby, it is #{}. In Perl, it could be $, % or @. Java would only print such characters, it would not expand them.
Variable interpolation is not supported in Java. Instead of this, we have string formatting.
package com.zetcode;
public class StringFormatting
{
public static void main(String[] args)
{
int age = 34;
String name = "William";
String output = String.format("%s is %d years old.", name, age);
System.out.println(output);
}
}
In Java, we build a new string using the String.format() method. The outcome is the same, but the methods are different.
See http://en.wikipedia.org/wiki/Variable_interpolation
Edit As of 2019, JEP 326 (Raw String Literals) was withdrawn and superseded by multiple JEPs eventually leading to JEP 378: Text Blocks delivered in Java 15.
A text block is a multi-line string literal that avoids the need for most escape sequences, automatically formats the string in a predictable way, and gives the developer control over the format when desired.
However, still no string interpolation:
Non-Goals: … Text blocks do not directly support string interpolation. Interpolation may be considered in a future JEP. In the meantime, the new instance method
String::formatted
aids in situations where interpolation might be desired.