TradeRecord.java

public class TradeRecord {
    public final int    tradeId;
    public final int    buyOrderId;
    public final int    sellOrderId;
    public final double price;
    public final int    quantity;
    public final long   executedAt; // System.nanoTime() at match time

    public TradeRecord(int tradeId, int buyOrderId, int sellOrderId,
                       double price, int quantity) {
        this.tradeId     = tradeId;
        this.buyOrderId  = buyOrderId;
        this.sellOrderId = sellOrderId;
        this.price       = price;
        this.quantity    = quantity;
        this.executedAt  = System.nanoTime();
    }

    @Override
    public String toString() {
        return String.format("Trade #%d | BUY #%d x SELL #%d | $%.2f x %d shares",
            tradeId, buyOrderId, sellOrderId, price, quantity);
    }
}