读取的时候，一个key只有一个value啊，所以是不是hashcode相同的时候会覆盖以前的value？那放在链表里的...
// HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stwRandom ; // * A variation of Marsaglia's shift-xor RNG scheme. // * (obj ^ stwRandom) is appealing, but can result // in undesirable regularity in the hashCode values of adjacent objects // (objects allocated ...
hashCode方法返回的是一个int值,可以看做是一个对象的唯一编码,如果两个对象的hashCode值相同,我们应该认为这两个对象是同一个对象。 一般如果使用java中的Map对象进行存储时,他会自动调用hashCode方法来比较两个对象是否相等。 所以如果我们对equals方法进行了重写,建议一定要对hashCode方法重写,以保证相同的对象返回相同...
value = os::random() ;//返回随机数 } else if (hashCode == 1) { // This variation has the property of being stable (idempotent) // between STW operations. This can be useful in some of the 1-0 // synchronization schemes. //和地址相关,但不是地址;右移+异或算法 intptr_t addrBits...
那么在内存中关键字(str)和存储值(value)是怎样存储的呢?如下: 这样就将Key 与 Value 之间生成一种映射关系 2、这个hashCode()方法非常有用,在所有的与Hash字眼相关的类(姑且称为hash类)中,这个方法是非常重要的,而且这些hash类几乎都必须重写这个方法,以便是该类能够正常运行 ...
下面这段代码是java.util.HashMap的中put方法的具体实现: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 public V put(K key, V value) { if (key == null) return putForNullKey(value); int hash = hash(key.hashCode()); int i = indexFor(hash, table.length); for (...
对于原因1中提到的位运算效率,比较好理解。位运算必然超过乘法运算。Stack Overflow 上关于这个问题的讨论,其中排名第一的答案引用了《EffectiveJava》中的一段话,这里也引用一下: The value 31 was chosen because it is an odd prime. If it were even and the multiplication overflowed, information would be ...
最多的这个回答是来自《Effective Java》的内容; The value 31 was chosen because it is an odd prime. If it were even and the multiplication overflowed, information would be lost, as multiplication by 2 is equivalent to shifting. The advantage of using a prime is less clear, but it is tradit...
value = os::random() ; }else if(hashCode ==1) { // This variation has the property of being stable (idempotent) // between STW operations. This can be useful in some of the 1-0 // synchronization schemes. intptr_t addrBit...
接下来我会用详细的实验来验证上面的结论,不过在验证前,我们先看看 Stack Overflow 上关于这个问题的讨论,Why does Java's hashCode() in String use 31 as a multiplier?。其中排名第一的答案引用了《EffectiveJava》中的一段话,这里也引用一下: The value 31 was chosen because it is an odd prime. If ...