String variable interpolation Java
If you're using Java 5 or higher, you can use String.format
:
urlString += String.format("u1=%s;u2=%s;u3=%s;u4=%s;", u1, u2, u3, u4);
See Formatter
for details.
String interpolation in Java 14 or 15
There is something slightly closer; an instance version of String::format
, called formatted
:
String message = "Hi, %s".formatted(name);
It is similar to String::format
, but is more friendly to use in chained expressions.
Does Java 8 support interpolation
Java8 has nothing to do with this. For formatted console output, you can use printf()
or the format()
method of System.out
Try this out.
System.out.printf("My name is: %s%n", "Tom");
How to interpolate variables within a string using HashMap as variable source
You would have to use some regex, parse the input and lookup every key in the Map, like that:
import java.util.Map;
import java.util.regex.Pattern;
public class T2 {
/** Pattern for the variables syntax */
public static final Pattern PATTERN = Pattern.compile("\\$\\$([a-zA-Z]+);");
public static void main(String[] args) {
String s = "Hello my name is $$name; and my surname is $$surname;";
Map<String, String> variables = Map.of("name", "John", "surname", "Doe");
String ret = replaceVariables(s, variables);
System.out.println(ret);
}
private static String replaceVariables(final CharSequence s, final Map<? super String, String> variables) {
return PATTERN.matcher(s).replaceAll(mr -> variables.getOrDefault(mr.group(1), ""));
}
}
Output:
Hello my name is John and my surname is Doe
How can i add variables inside Java 15 text block feature?
From the spec for text blocks:
Text blocks do not directly support string interpolation.
Interpolation may be considered in a future JEP.
"String interpolation" meaning
evaluating a string literal containing one or more placeholders,
yielding a result in which the placeholders are replaced with their
corresponding values
from Wikipedia
As stated above, maybe we'll get it in the future. Though it is difficult to say how they could possibly implement that without breaking backwards compatibility -- what happens if my string contains ${}
, for example? The Java language designers rarely add anything that is likely to break backwards compatibility.
It seems to me that they would be better off either supporting it immediately, or never.
Maybe it would be possible with a new kind of text block. Rather than the delimiter being """
, they could use '''
to denote a parameterized text block, for example.
String Formatting Java
What you are looking for is interpolation (the detection and replacement with its value) of variables or expressions inside String literals. Java has no such feature. In Java, you will have to revert to:
- String concatenation, for example
StringBuilder.append()
- String formatting, for example
PrintStream.printf()
,PrintWriter.printf()
,String.format()
alternative for strings combing strings that isnt +
See https://docs.oracle.com/javase/7/docs/api/java/lang/String.html
String.format("Hello %s. Today is %s.", userName, date);
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