详谈Map的key、value值的数据类型不能为基本类型的原因

  /**
     * Returns the hash code value for this map entry. The hash code
     * of a map entry <tt>e</tt> is defined to be: <pre>
     *   (e.getKey()==null  ? 0 : e.getKey().hashCode()) ^
     *   (e.getValue()==null ? 0 : e.getValue().hashCode())
     * </pre>
     * This ensures that <tt>e1.equals(e2)</tt> implies that
     * <tt>e1.hashCode()==e2.hashCode()</tt> for any two Entries
     * <tt>e1</tt> and <tt>e2</tt>, as required by the general
     * contract of <tt>Object.hashCode</tt>.
     *
     * @return the hash code value for this map entry
     * @see Object#hashCode()
     * @see Object#equals(Object)
     * @see #equals(Object)
  */
    int hashCode();

public final int hashCode() {
 return Objects.hashCode(key) ^ Objects.hashCode(value);
}

static final int hash(Object key) {
 int h;
 return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}

public final boolean equals(Object o) {
 if (o == this)
    return true;
  if (o instanceof Map.Entry) {
    Map.Entry<?,?> e = (Map.Entry<?,?>)o;
  if (Objects.equals(key, e.getKey()) &&
    Objects.equals(value, e.getValue()))
    return true;
  }
  return false;
}

Map<Object,String> map = new HashMap<>();
Integer b = 123;
Long c =123L;
map.put(b, b+"int");
System.out.println(b.hashCode() == c.hashCode()); //true
System.out.println(map.get(c));  //null
map.put(c, c+"long"); // size =2

if (obj instanceof Integer) {
      return value == ((Integer)obj).intValue();
    }

return false;