搜索词已经转义，为什么替换成 $1 仍然变了？

import java.util.regex.*;
public class RegexLiteralDemo {
    static int checks;
    static void check(boolean ok) { if (!ok) throw new AssertionError(); checks++; }
    static String literalReplace(String input, String needle, String replacement) {
        if (needle.isEmpty()) throw new IllegalArgumentException("empty search is undefined here");
        return Pattern.compile(Pattern.quote(needle)).matcher(input)
                .replaceAll(Matcher.quoteReplacement(replacement));
    }
    public static void main(String[] args) {
        String input = "a.b axb a.b";
        String unquoted = Pattern.compile("a.b").matcher(input).replaceAll("X");
        String searchOnly = Pattern.compile(Pattern.quote("a.b")).matcher(input).replaceAll("X");
        check(unquoted.equals("X X X")); check(searchOnly.equals("X axb X"));
        System.out.println("unquoted_search=" + unquoted);
        System.out.println("quoted_search=" + searchOnly);
        Pattern grouped = Pattern.compile("(a\\.b)");
        String interpreted = grouped.matcher("a.b").replaceAll("$1");
        String literal = grouped.matcher("a.b").replaceAll(Matcher.quoteReplacement("$1"));
        check(interpreted.equals("a.b")); check(literal.equals("$1"));
        System.out.println("replacement_$1: interpreted=" + interpreted + "; literal=" + literal);
        String replacement = "$1\\archive";
        String result = literalReplace(input, "a.b", replacement);
        check(result.equals("$1\\archive axb $1\\archive"));
        check(result.equals(input.replace("a.b", replacement)));
        System.out.println("both_literal=" + result);
        String odd = "left\\E.right";
        check(literalReplace("<" + odd + ">", odd, "$0").equals("<$0>"));
        check(literalReplace("no match", "a.b", "$1").equals("no match"));
        boolean emptyRejected=false;
        try { literalReplace("abc", "", "X"); } catch (IllegalArgumentException e) { emptyRejected=true; }
        check(emptyRejected);
        System.out.println("embedded_quote_end=preserved; absent_match=unchanged; empty_search=rejected");
        System.out.println("PASS checks=" + checks);
    }
}