how do I get list of all "used" addresses in bitcoinj
This seems to get change addresses:

public List&lt;String&gt; getChangeAddresses() {
    List&lt;String&gt; ret = new ArrayList&lt;&gt;();
    int issuedKeys = wallet.getActiveKeyChain().getIssuedInternalKeys();

    for (int i = 0; i &lt; issuedKeys; i++) {
        ChildNumber childNumber = new ChildNumber(i, false);
        List&lt;ChildNumber&gt; childNumbers = new ArrayList&lt;&gt;();
        childNumbers.add(ChildNumber.ZERO_HARDENED);
        childNumbers.add(ChildNumber.ONE);
        childNumbers.add(childNumber);
        ECKey key = wallet.getKeyByPath(childNumbers);
        ret.add(new Address(params, key.getPubKeyHash()).toBase58());
    }
    return ret;
}