搞懂JAVAObject中的hashCode()

 public native int hashCode();

static inline intptr_t get_next_hash(Thread * Self, oop obj) {
  intptr_t value = 0 ;
  if (hashCode == 0) {
     // 返回随机数
     value = os::random() ;
  } else
  if (hashCode == 1) {
     //用对象的内存地址根据某种算法进行计算
     intptr_t addrBits = cast_from_oop<intptr_t>(obj) >> 3 ;
     value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
  } else
  if (hashCode == 2) {
     // 始终返回1，用于测试
     value = 1 ;            
  } else
  if (hashCode == 3) {
     //从0开始计算哈希值
     value = ++GVars.hcSequence ;
  } else
  if (hashCode == 4) {
     //输出对象的内存地址
     value = cast_from_oop<intptr_t>(obj) ;
  } else {
     // 默认的hashCode生成算法，利用xor-shift算法产生伪随机数
     unsigned t = Self->_hashStateX ;
     t ^= (t << 11) ;
     Self->_hashStateX = Self->_hashStateY ;
     Self->_hashStateY = Self->_hashStateZ ;
     Self->_hashStateZ = Self->_hashStateW ;
     unsigned v = Self->_hashStateW ;
     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
     Self->_hashStateW = v ;
     value = v ;
  }

  value &= markOopDesc::hash_mask;
  if (value == 0) value = 0xBAD ;
  assert (value != markOopDesc::no_hash, "invariant") ;
  TEVENT (hashCode: GENERATE) ;
  return value;
}

import java.util.HashMap;
import java.util.Objects;


public class Person {
    //用户Id，唯一确定用户
    private String id;
    private String name;

    public Person(String id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Person)) return false;
        Person person = (Person) o;
        return Objects.equals(id, person.id) && Objects.equals(name, person.name);
    }

    public static void main(String[] args) {
        HashMap<Person, Integer> map = new HashMap<>();
        //key:Person类型  value:Integer类型
        map.put(new Person("1","张三"),100);
        System.out.println(map.get(new Person("1", "张三")));
    }
}

if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
     return first;

  @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }

  public static int hashCode(int value) {
        return value;
    }