/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
import java.util.regex.*;
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String[] operatorList = { "name", "first_name", "last_name", "city" };
		// assuming operators only consist of word chars
		String pat = "(\\b|\\^(?:OR|AND)?)(" + String.join("|", operatorList) + ")\\b";
		System.out.println(pat);
		String originalString = "city=Houston^ORlast_name=Cervantsz^ORfirst_name=John^name=don";
		originalString = originalString.replaceAll(pat, "$1user.$2");
		System.out.println(originalString);
	}
}

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