2021-08 常用API

集合的工具类总结：

1. com.google.common.collect.Maps#newHashMapWithExpectedSize;
2. com.google.common.collect.Maps#difference(java.util.Map<? extends K,? extends V>, java.util.Map<? extends K,? extends V>);
3. com.google.common.collect.MapDifference#entriesOnlyOnLeft;
4. com.google.common.collect.MapDifference#entriesOnlyOnRight;
5. com.google.common.collect.MapDifference#entriesDiffering;
6. com.google.common.collect.Sets#symmetricDifference;