标题: hashCode返回的值是如何计算出来的呢 [打印本页] 作者: 李龙涛 时间: 2011-7-22 19:14 标题: hashCode返回的值是如何计算出来的呢 hashCode方法是在哪个类中被定义的呢？不同的类的hashCode方法是不是覆盖掉父类的hashCode方法而来的呢？那我可以这样理解吗：不同类的hashCode方法的返回值，是由不同的代码块计算出来的。作者: 匿名 时间: 2011-7-22 19:46
恩 可以那么理解，如果一个类重写了hashcode方法，就调用它的hashcode方法，如果没有就调用它父类的hashcode方法。如果还没有就找他的父类的父类，最后到Object类。Object有最后的hashcode方法....作者: 匿名 时间: 2011-7-22 20:02
java中所有的类都默认继承Object，hashcode是在Object中定义出来的，有时我们需要重写hashCode方法。
jdk文档中是这样写的hashCode
public int hashCode()
Returns a hash code value for the object. This method is supported for the benefit of hashtables such as those provided by java.util.Hashtable.
The general contract of hashCode is:
Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.
As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)
Returns:
a hash code value for this object.
See Also:
equals(java.lang.Object), Hashtable
该方法在 Object 类中是这样定义的 public native int hashCode();