reflect permission and security manage in java

import java.lang.reflect.Field;
import java.lang.reflect.ReflectPermission;

public class ReflectField {

private String test = "test string in class ReflectField!";

public static void main(String[] args) throws Exception {
Class ref = ReflectField.class;

SecurityManager nsm = new SecurityManager();
System.setSecurityManager(nsm);
ReflectPermission rp = new ReflectPermission("suppressAccessChecks", null);
System.out.println(rp);
// java.security.AccessControlException:
// access denied (java.lang.reflect.ReflectPermission suppressAccessChecks
// nsm.checkPermission(rp);
SecurityManager sm = System.getSecurityManager();
System.out.println(sm);

Field[] fields = ref.getDeclaredFields();
System.out.println(fields.length);
for (Field field : fields) {
// java.security.AccessControlException:
// access denied (java.lang.reflect.ReflectPermission suppressAccessChecks
// field.setAccessible(true);

// java.lang.IllegalArgumentException
// at sun.reflect.UnsafeFieldAccessorImpl.ensureObj(UnsafeFieldAccessorImpl.java)
// System.out.println(field.get(ref));

System.out.println(field.getName());
}

}

}

This main method had set a security manage to this java application, in order to prevent java reflect get and set private fields.