Make sense of Notification Watcher source objective-c

From Notification Watcher source.

- (void)selectNotification:(NSNotification*)aNotification {
id sender = [aNotification object];
[selectedDistNotification release];
selectedDistNotification = nil;
[selectedWSNotification release];
selectedWSNotification = nil;
NSNotification **targetVar;
NSArray **targetList;
if (sender == distNotificationList) {
    targetVar = &selectedDistNotification;
    targetList = &distNotifications;
} else {
    targetVar = &selectedWSNotification;
    targetList = &wsNotifications;
}
if ([sender selectedRow] != -1) {
    [*targetVar autorelease];
    *targetVar = [[*targetList objectAtIndex:[sender selectedRow]] retain];
}
if (*targetVar == nil) {
    [objectText setStringValue:@""];
} else {
    id obj = [*targetVar object];
    NSMutableAttributedString *objStr = nil;
    if (obj == nil) {
        NSFont *aFont = [objectText font];
        NSDictionary *attrDict = italicAttributesForFont(aFont);
        objStr = [[NSMutableAttributedString alloc] initWithString:@"(null)"
                                                        attributes:attrDict];
    } else {
/* Line 1 */        objStr = [[NSMutableAttributedString alloc] initWithString:
                    [NSString stringWithFormat:@" (%@)", [obj className]]];
        [objStr addAttributes:italicAttributesForFont([objectText font])
                        range:NSMakeRange(1,[[obj className] length]+2)];
        if ([obj isKindOfClass:[NSString class]]) {
            [objStr replaceCharactersInRange:NSMakeRange(0,0) withString:obj];
        } else if ([obj respondsToSelector:@selector(stringValue)]) {
            [objStr replaceCharactersInRange:NSMakeRange(0,0)
                                  withString:[obj performSelector:@selector(stringValue)]];
        } else {
            // Remove the space since we have no value to display
 开发者_如何学C           [objStr replaceCharactersInRange:NSMakeRange(0,1) withString:@""];
        }
    }
    [objectText setObjectValue:objStr];
/* LINE 2 */    [objStr release];
}
[userInfoList reloadData];

}

Over at //LINE 2 objStr is being released. Is this because we are assigning it with alloc in //LINE 1?

Also, why is //LINE 1 not:

objStr = [NSMutableAttributedString* initWithString:@"(null)"
                                                    attributes:attrDict]

If I create a new string like

(NSString*) str = [NSString initWithString:@"test"];
...
str = @"another string";

Would I have to release str, or is this wrong and if I do that I have to use [[NSString alloc] initWithString:@"test"]? Why isn't the pointer symbol used as in [[NSString* alloc] ...?

Thanks

It is being released because it was allocated. The alloc has the effect of a retain and must be balanced by a release (or autorelease). Pretty much any method that begins with init results in an object that needs to be released. It is all about balancing the retains with the releases.