Detailed usage of Java HashSet function, storage mechanisms and performance analysis

HashSet storage mechanism:

• With a length of the underlying storage element array, and the array is always the n-th power of 2, if the incoming length of the array is not n-th power of 2, HashSet it will automatically extend to the n-th power of 2;
• HashSet constructor:

HashSet(int initialCapacity, float loadFactor)
//initialCapacity——控制底层数组长度
//loadFactor——当HashSet感觉到底层快要满的时候（0.75），会将底层数组容量扩充1倍，
//原来的数组就变成垃圾，等待回收，即rehash（重hash）
//说明：当LoadFactor为0.75时，75%的桶已满，HashSet会分配新的数组；LoadFactor越小，
//越消耗内存；LoadFactor越大，性能越低
//数组越满，才回去“重hash”，越有可能出现链表

• HashSet into the mechanism:

1. When all elements add to the mix, the object is invoked HashSet HashCode () method, to obtain an int value;
2. The int value returned HashCode (), which is calculated in the bottom HashSet [] array of storage locations (indexed array);
3. If no element to be added is a position (is empty), directly into the can;
4. If you want to add the element position has been, where it will form a "chain"

• HashSet take elements of mechanisms:

1. When we want to take an element, the object is invoked HashSet HashCode () method, to obtain an int value;
2. The int value returned HashCode (), which calculates the storage position (the index of the array) at a HashSet;
3. If the location is exactly looking element can be taken directly;
4. If the location has a list, HashSet to "one by one" in the search list elements

Description: In the best case, the performance is almost HashSet array match, to deposit, withdraw very high performance

• HashSet two objects are considered equal conditions:

1. HashCode two objects () is equal to the return value;
2. Compare the two objects are also returned by equals True