若不重写User类的hashCode与equals方法的话,则会使用Object类定义的默认实现,即:hashCode是 JVM 生成的一个伪随机数,equals比较的是两个引用的地址。 下面测试代码新建了两个逻辑上「相等」的User对象:user1与user2,然后比较user1.equals(user2)与user1.hashCode() == user2.hashCode(),发现结果均为false;然后...
/*** Returns a hash code value for the object. This method is* supported for the benefit of hash tables such as those provided by* {@link java.util.HashMap}.* * The general contract of {@code hashCode} is:* * Whenever it is invoked on the same object more than once during* an ...
The general contractofhashCodeis: Whenever itisinvokedonthe sameobjectmore than once during an executionofa Java application, the hashCode method must consistentlyreturnthe sameinteger, provided no information usedinequalscomparisonsontheobjectismodified. Thisintegerneednotremain consistentfromone executionofan...
hashCode 一般与 equals 一起使用,两个对象作「相等」比较时,因判断 hashCode 是判断 equals 的先决条件. 为什么一个类中需要两个比较方法 因为重写的 equals() 里一般比较的比较全面比较复杂,这样效率就比较低,而利用hashCode()进行对比,则只要生成一个 hash 值进行比较就可以了,效率很高,那么 hashCode() 既然效...
* The general contract of {@code hashCode} is: * * Whenever it is invoked on the same object more than once during * an execution of a Java application, the {@code hashCode} method * must consistently return the same integer, provided no information * used in...
java 代码解读复制代码packagejava.lang;publicclassObject{/** * Returns a hash code value for the object. This method is * supported for the benefit of hash tables such as those provided by * `java.util.HashMap`. * * The general contract of `hashCode` is: ...
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...
java意识到存在这样的效率低下问题,引入了hashCode方法,可以大大提高判断重复的效率。既然引入了hashCode方法,那么大家在重写hashCode方法的时候,就需要遵守java的约定。 三、equals方法与hashCode方法的契约 Object的hashCode方法上有这样的注释 * *Thegeneralcontractof{@codehashCode}is: * *...
如下为hashCode方法在Object类中的定义: java 代码解读 复制代码 packagejava.lang;publicclassObject{/*** Returns a hash code value for the object. This method is* supported for the benefit of hash tables such as those provided by* `java.util.HashMap`.** The general contract of `hashCode` is...
3.1. The .hashCode()Contract Java SE also defines a contract for the .hashCode()method. A thorough look at this contract reveals how closely related .hashCode()and .equals()are. All three criteria in the .hashCode()contract mention the .equals()method in some way: ...