How to replace first word in flutter or dart

for Example: “This is an Apple” replace “is” to “__”,

in java

public class HelloWorld {
    public static void main(String []args) {
       String a="This is an Apple";
       String b=a.replaceFirst("\bis\b","__");
       System.out.println(b);// This __ an Apple
    }
}

but in flutter or dart \b is not working。

void main(){
    String a="This is an Apple";
    String b=a.replaceFirst("\bis\b","__");
    print(b);//This is an Apple
}

I think you should use ‘\s’ instead of ‘\b’. See the example below

void main() 
{
  final originalString = 'This is an Apple';
  final replacedString = originalString.replaceFirst(RegExp('\sis\s'), ' __ ');
  print(replacedString);  // This __ an Apple
}

try with this for single space

void main(){
    String a="This is an Apple";
    String b=a.replaceFirst(new RegExp(r"siss")," __ ");
    print(b);//This __ an Apple
}

output:
This __ an Apple

Another method:

void main(){
    String a="This is an Apple";
    String b=a.replaceFirst(" is "," __ ");
    print(b);//This __ an Apple
}