Barang itu bukannya barang bekas, melainkan barang antik.

Barang is a general word meaning thing, item, goods, object. In this sentence, it refers to the item being discussed.

It appears three times because Indonesian often repeats the noun for clarity in a contrast pattern:

• Barang itu = that item / that thing
• barang bekas = a used item / secondhand goods
• barang antik = an antique item

So the repetition helps make the contrast very explicit:
That item is not a used item, but rather an antique item.

In natural speech, Indonesian sometimes allows omission if the meaning is obvious, but repeating barang here is completely normal and clear.

Itu usually means that.

So:

• barang itu = that item / that thing

It points to a specific item already known in the conversation.

A useful comparison:

• barang ini = this item
• barang itu = that item

Indonesian often omits the verb to be when linking a subject to a noun or adjective.

So English says:

• That item is not secondhand, but antique.

Indonesian can simply say:

• Barang itu bukannya barang bekas, melainkan barang antik.

There is no need for is. This is very normal Indonesian grammar.

Sometimes you may see adalah, but it is often unnecessary in ordinary sentences and can sound more formal or explanatory.

Here, bukannya introduces a correction or contrast, something like:

• not actually
• it’s not that ...
• not ... but rather ...

In this sentence, bukannya works together with melainkan:

• bukannya ..., melainkan ...
• not ..., but rather ...

So the structure is:

• bukannya barang bekas = not a secondhand item
• melainkan barang antik = but rather an antique item

This is a strong way to correct a mistaken assumption.

Bukan is the basic negator for nouns and noun phrases.

Examples:

• Itu bukan mobil saya. = That is not my car.
• Ini bukan barang bekas. = This is not a used item.

Bukannya is often more contrastive or corrective. It frequently appears when the speaker is saying:

• not X, but Y
• it’s not that X; rather Y

So in your sentence, bukannya sounds more natural because the speaker is correcting a classification:

• not secondhand
• but antique

If you said:

• Barang itu bukan barang bekas, melainkan barang antik.

that is also grammatical and natural.
Using bukannya adds a little more emphasis to the correction.

Melainkan means but rather, but instead, or rather in a contrastive sense.

It is commonly used after a negation:

• bukan/bukannya ..., melainkan ...
• not ..., but rather ...

So:

• bukannya barang bekas, melainkan barang antik
• not secondhand, but rather antique

Compared with tapi or tetapi, melainkan sounds a bit more formal and more precise in this kind of correction.

For example:

• Itu bukan kesalahan saya, melainkan kesalahannya.
  = It’s not my mistake, but rather his/hers.

Because bekas and antik are describing the noun barang.

• barang bekas = used item / secondhand goods
• barang antik = antique item

In Indonesian, modifiers usually come after the noun, so:

• rumah besar = big house
• mobil baru = new car
• barang antik = antique item

Could you shorten it? Sometimes yes, especially if the noun is already clear from context. But in this sentence, repeating barang keeps the contrast neat and parallel.

This is an important vocabulary distinction.

Bekas means used, secondhand, previously owned. It does not automatically imply value or age.

• baju bekas = used clothes
• mobil bekas = a used car

Antik means antique, something old and often valuable, rare, or historically interesting.

So an object can be:

• bekas only: just used
• antik: old and valuable
• sometimes both in a broad sense, but in this sentence they are contrasted as different categories

The sentence is basically correcting the idea that the item is merely used; instead, it is an antique.

Yes, the word order is normal Indonesian.

In Indonesian, adjectives and many modifiers usually come after the noun:

• barang bekas = used item
• barang antik = antique item
• rumah tua = old house
• buku baru = new book

So unlike English, which says antique item, Indonesian says barang antik.

That is one of the most basic word-order differences English speakers need to get used to.

Yes. A more everyday version might be:

• Barang itu bukan barang bekas, tapi barang antik.
• Itu bukan barang bekas, tapi barang antik.

These are more conversational because tapi is more common in speech than melainkan.

The original sentence with bukannya ... melainkan ... sounds a bit more deliberate, polished, or emphatic, especially when correcting someone.

By itself, barang does not clearly mark singular or plural the way English does.

So depending on context, it could mean:

• item / thing
• goods / items

In this sentence, because of barang itu and the way it is discussed, many learners will naturally understand it as that item. But Indonesian often leaves number to context.

If a speaker really wanted to emphasize plural, they might say:

• barang-barang itu = those items / those goods

Yes. This can confuse learners.

In this sentence, bukannya is part of a contrast:
not ..., but rather ...

But in other contexts, bukannya can also introduce something like:

• instead of
• rather than
• a complaint about what someone did

For example:

• Bukannya belajar, dia malah main game.
  = Instead of studying, he played games.

So the exact meaning of bukannya depends on the structure around it.
In your sentence, because it is paired with melainkan, the meaning is clearly not X, but rather Y.