PatternSyntaxException: while using String.ReplaceAll function in java?

I got a patternsyntax exception when i am trying to do a String.ReplaceAll.

Below is my String

Number of testcases to execute : 39?    Starting execution of test case : testCreateDAta?    The class that has completed its execution is : test.com.mySpace.service.ejb.session.MyTest?     Finished execution of test case : testCreateDAta?    Starting execution of test case : testUpdate?

What i was trying to do:

junitReportString.replaceAll("?", "\n"); 

The above code fetched me the below exception:

java.util.regex.PatternSyntaxException: Dangling meta character '?' near index 0 

Then i tried again with the below code:

junitReportString.replaceAll("\\?", "\n"); 

The above code fetched me the same String that i mentioned above.

My Complete Code:

String junitReportString=new String();
myApp= new URL("http://localhost:port/testWeb/TestJunit.jsp");
URLConnection yc = myApp.openConnection();
yc.connect();
junitReportString=yc.getHeaderField("finalJUNITReport").toString();
System.out.println(junitReportString);
junitReportString.replaceAll("\\?", "\n");
System.out.println("Report Details     ==============>"+junitReportString);

What is wrong with my code. Any guidance much appreciated.