testing String as immutable

[Mike Cunningham]

Is there a way to test that a String is immutable by attempting to change the actual string object in the constant pool?

[R K Singh]

mean ??

[WiLL Tao]

Is this code ok?
because "==" is shallow compare,so if string is mutable, the refence address will not be changed.
but this code provdes m1 create new ojbect.

  class TestString 
{
public static void main(String[] args) 
{
String m1=new String("test");
String m2;
m2=m1;
System.out.println(m1);
if (m1==m2)
{
System.out.println("ADDRESS EQUAL");
}
m1="test" + "1";
System.out.println(m1);
if (m1==m2)
{
System.out.println("ADDRESS EQUAL"); //false
}
}
}