public static  void checkPermission(Permission perm) throws AccessControlException 
{
        if (perm == null) {
            throw new NullPointerException("permission can not be null");
        }
        getContext().checkPermission(perm);
}

 public static T doPrivileged(PrivilegedAction<T> action) 
{
        if (action == null) {
            throw new NullPointerException("action can not be null");
        }
        return doPrivilegedImpl(action, null);
}

 public static T doPrivileged(PrivilegedExceptionAction<T> action) throws PrivilegedActionException 
{
        if (action == null) {
            throw new NullPointerException("action can not be null");
        }
        return doPrivilegedImpl(action, null);
}

 public static T doPrivileged(PrivilegedAction<T> action,
    AccessControlContext context) 
{
        if (action == null) {
            throw new NullPointerException("action can not be null");
        }
        return doPrivilegedImpl(action, context);
}

 public static T doPrivileged(PrivilegedExceptionAction<T> action,
    AccessControlContext context) throws PrivilegedActionException 
{
        if (action == null) {
            throw new NullPointerException("action can not be null");
        }
        return doPrivilegedImpl(action, context);
}

 public static AccessControlContext getContext() 
{
        // duplicates (if any) will be removed in ACC constructor
        ProtectionDomain[] stack = getStackDomains();
        Thread currThread = Thread.currentThread();
        if (currThread == null || contexts == null) {
            // Big boo time. No need to check anything ? 
            return new AccessControlContext(stack);
        }
        ArrayList< AccessControlContext > threadContexts;
        synchronized (contexts) {
            threadContexts = contexts.get(currThread);
        }
        AccessControlContext that;
        if ((threadContexts == null) || (threadContexts.size() == 0)) {
            // We were not in doPrivileged method, so
            // have inherited context here
            that = SecurityUtils.getContext(currThread);
        } else {
            // We were in doPrivileged method, so
            // Use context passed to the doPrivileged()
            that = threadContexts.get(threadContexts.size() - 1);
        }
        if (that != null && that.combiner != null) {
            ProtectionDomain[] assigned = null;
            if (that.context != null && that.context.length != 0) {
                    assigned = new ProtectionDomain[that.context.length];
                    System.arraycopy(that.context, 0, assigned, 0,
                            assigned.length);
            }
            ProtectionDomain[] allpds = that.combiner.combine(stack, assigned);
            if (allpds == null) {
                allpds = new ProtectionDomain[0];
            }
            return new AccessControlContext(allpds, that.combiner);
        }
        return new AccessControlContext(stack, that);
}