@Override
    public String toString() {
        final StringBuilder buf = new StringBuilder("{");
        forEachEntry(new BiFunction<Long, Integer, Boolean>() {
            private boolean first = true;

            @Override
            public Boolean apply(Long key, Integer value) {
                if (first) {
                    first = false;
                } else {
                    buf.append(", ");
                }
                buf.append(key);
                buf.append("=");
                buf.append(value);
                return true;
            }
        });
        buf.append("}");
        return buf.toString();
    }
Look until FREE slot or we start to loop
core/src/main/java/com/alibaba/fastjson2/internal/trove/map/hash/TLongIntHashMap.java