问Regex: PatternSyntaxException:非法重复

EN

public class method3 {

    public static int addTwoNumbers(int one, int two){
        return one+two;
    }

    public static void main (String[] args){
        int total = addTwoNumbers(1, 3);
        System.out.println(total);
    }
}

null
public class method3 {
    /* some writting */
    public static int addTwoNumbers(int one, int two){
        return one+two;
    }
    /*more text*/
    public static void main (String[] args){
        int total = addTwoNumbers(1, 3);
        System.out.println(total);
    }//end of 
}

java.util.regex.PatternSyntaxException: Illegal repetition

Exception in thread "AWT-EventQueue-0" java.util.regex.PatternSyntaxException: Illegal repetition near index 25
null
public class method2 {

    public static int addTwoNumbers(int one, int two){
        return one+two;
    }

    public static void main (String[] args){
        int total = addTwoNumbers(1, 3);
        System.out.println(total);
    }
}


                         ^
    at java.util.regex.Pattern.error(Pattern.java:1924)
    at java.util.regex.Pattern.closure(Pattern.java:3104)
    at java.util.regex.Pattern.sequence(Pattern.java:2101)
    at java.util.regex.Pattern.expr(Pattern.java:1964)
    at java.util.regex.Pattern.compile(Pattern.java:1665)
    at java.util.regex.Pattern.<init>(Pattern.java:1337)
    ....

        String a = readFile(directoryToAddFile,startOfCode, endOfCode);
        String b = textarea.getText().toString();
        String content = IOUtils.toString(new FileInputStream(directoryToAddFile));
        content = content.replaceAll(a, b);
        IOUtils.write(content, new FileOutputStream(directoryToAddFile));