NSArray * list1 = [NSArray arrayWithObjects:@"a", @"b", @"c", nil];NSArray * list2 = @[@"1", @"2", @"3"];

NSDictionary * hash1 = [NSDictionary dictionaryWithObjects:@[@"1", @"2", @"3"]
                                                   forKeys:@[@"a", @"b", @"c"]];
NSDictionary * hash2 = @ {
    @"a" : @"1",
    @"b" : @"2",
    @"c" : @"3"
}

NSNumber * number1 = [NSNumbernumberWithInt:12345];
NSNumber * number2 = @12345;

arr[@1]      === [arr objectAtIndex:1]
dict[@1]     === [dict objectAtIndex:1]
dict[@"key"] === [dict objectForKey:@"key"]