后置条件的Java断言

Question

我正在尝试了解Java断言。我有以下方法，我想添加一个后置条件断言。我不确定自己做的是否正确，是否有人可以对我说清楚并告诉我是否正确，或者为什么？

chain是组成链的块的列表，每个块都由字节数组表示。

boolean addBlock (byte[] block) {

    // Prepare for correctness check
    byte[] last = getLast();
    byte[] last_data_hash = new byte[hash_size];
    byte[] current_link_hash = new byte[hash_size];
    for (int i=0; i < hash_size; i++) {
        last_data_hash[i] = last[hash_size+i];
        current_link_hash[i] = block[i];
    }

    if (Arrays.equals(current_link_hash,last_data_hash)) {
        // if it is correctly linked, add it
        chain.add(block.clone());
        return true;
    } else // if it is not correctly linked, don't add it
        return false;

    assert (chain == null) : "chain list: " + chain ;
}

编辑：

boolean addBlock (byte[] block) {

        // Prepare for correctness check
        byte[] last = getLast();
        byte[] last_data_hash = new byte[hash_size];
        byte[] current_link_hash = new byte[hash_size];
        for (int i=0; i < hash_size; i++) {
            last_data_hash[i] = last[hash_size+i];
            current_link_hash[i] = block[i];
        }

        if (Arrays.equals(current_link_hash,last_data_hash)) {
            // if it is correctly linked, add it
            chain.add(block.clone());
            **assert (chain == null) : "chain list: " + chain ;**
            return true;
        } else // if it is not correctly linked, don't add it
            return false;


    }