String first="#listen_addresses = 'localhost' # what IP address(es) to listen on";
String second= "listen_addresses = '*'";
String third = first.replace("#listen_addresses\t=\t'localhost'", second);
System.out.println(third);

------解决方案--------------------
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first="#listen_addresses = 'localhost' # what IP address(es) to listen on";
替换后的结果是
first="listen_addresses = '*' # what IP address(es) to listen on";



是先在将first中找到"#listen_addresses = 'localh……


------解决方案--------------------
Java code

public class Test {
    public static void main(String[] args) {
    
    String first="#listen_addresses = 'localhost' # what IP address(es) to listen on";
    String second= "listen_addresses = '*'";
    String result = first.replace("#listen_addresses = 'localhost'", second);
    System.out.println(result);
    
    
    //根据我的测试，中间的空白符不是制表符 
    //但是上面的方法直接些\\s 又不行，所以写下面的方法，应该能满足你了
    String regex = "#listen_addresses\\s=\\s'localhost'";     
    Matcher matcher = Pattern.compile(regex).matcher(first);//
    result =  matcher.replaceAll(second);
    System.out.println(result);        
        
    }
}