Primitive question, but how do I format strings like this:
"Step {1} of {2}"
by substituting variables using Java? In C# it's easy.
This question is related to
java
string
string-formatting
If you choose not to use String.format, the other option is the + binary operator
String str = "Step " + a + " of " + b;
This is the equivalent of
new StringBuilder("Step ").append(String.valueOf(1)).append(" of ").append(String.valueOf(2));
Whichever you use is your choice. StringBuilder is faster, but the speed difference is marginal. I prefer to use the +
operator (which does a StringBuilder.append(String.valueOf(X)))
and find it easier to read.
This solution worked for me. I needed to create urls for a REST client dynamically so I created this method, so you just have to pass the restURL like this
/customer/{0}/user/{1}/order
and add as many params as you need:
public String createURL (String restURL, Object ... params) {
return new MessageFormat(restURL).format(params);
}
You just have to call this method like this:
createURL("/customer/{0}/user/{1}/order", 123, 321);
The output
"/customer/123/user/321/order"
I've wrote my simple method for it :
public class SomeCommons {
/** Message Format like 'Some String {0} / {1}' with arguments */
public static String msgFormat(String s, Object... args) {
return new MessageFormat(s).format(args);
}
}
so you can use it as:
SomeCommons.msfgFormat("Step {1} of {2}", 1 , "two");
Take a look at String.format. Note, however, that it takes format specifiers similar to those of C's printf family of functions -- for example:
String.format("Hello %s, %d", "world", 42);
Would return "Hello world, 42". You may find this helpful when learning about the format specifiers. Andy Thomas-Cramer was kind enough to leave this link in a comment below, which appears to point to the official spec. The most commonly used ones are:
This is radically different from C#, which uses positional references with an optional format specifier. That means that you can't do things like:
String.format("The {0} is repeated again: {0}", "word");
... without actually repeating the parameter passed to printf/format. (see The Scrum Meister's comment below)
If you just want to print the result directly, you may find System.out.printf (PrintStream.printf) to your liking.
There is a new instance method called String::formatted(Object... args)
as of Java 15.
The internal implementation is same to String::format(String format, Object... args)
.
Formats using this string as the format string, and the supplied arguments.
String step1 = "one";
String step2 = "two";
// results in "Step one of two"
String string = "Step %s of %s".formatted(step1, step2);
Advantage: The difference is that the method is not static
and the formatting pattern is a string itself from which a new one is created based on the args
. This allows chaining to build the format itself first.
Disadvantage: There is no overloaded method with Locale
, therefore uses the default one. If you need to use a custom Locale
, you have to stick with String::format(Locale l,String format,Object... args)
.
I wrote this function it does just the right thing. Interpolate a word starting with $
with the value of the variable of the same name.
private static String interpol1(String x){
Field[] ffield = Main.class.getDeclaredFields();
String[] test = x.split(" ") ;
for (String v : test ) {
for ( Field n: ffield ) {
if(v.startsWith("$") && ( n.getName().equals(v.substring(1)) )){
try {
x = x.replace("$" + v.substring(1), String.valueOf( n.get(null)));
}catch (Exception e){
System.out.println("");
}
}
}
}
return x;
}
public class StringFormat {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
System.out.println("================================");
for(int i=0;i<3;i++){
String s1=sc.next();
int x=sc.nextInt();
System.out.println(String.format("%-15s%03d",s1,x));
}
System.out.println("================================");
}
}
outpot "================================"
ved15space123 ved15space123 ved15space123 "================================
Java solution
The "-" is used to left indent
The "15" makes the String's minimum length it takes up be 15
The org.apache.commons.text.StringSubstitutor helper class from Apache Commons Text provides named variable substitution
Map<String, String> valuesMap = new HashMap<>();
valuesMap.put("animal", "quick brown fox");
valuesMap.put("target", "lazy dog");
String resolved = new StringSubstitutor(valuesMap).replace("The ${animal} jumped over the ${target}.");
System.out.println(resolved); // The quick brown fox jumped over the lazy dog.
Source: Stackoverflow.com