1.普通類(lèi)對(duì)象

1. hashCode相同，不一定是同一個(gè)對(duì)象
2. 同一個(gè)對(duì)象的，hashCode值一定相同

2. 數(shù)值型的原始數(shù)據(jù)類(lèi)型對(duì)應(yīng)的包裝類(lèi)

只要值是一樣的，hashCode就會(huì)是相同的。盡管不同的數(shù)值類(lèi)型的包裝類(lèi)，計(jì)算hashCode的算法不一樣，但是底層都是拿對(duì)應(yīng)的原始數(shù)據(jù)類(lèi)型的值去進(jìn)行hashCode計(jì)算。

以Double類(lèi)為例

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3. 測(cè)試代碼如下

/***hashCode相同，不一定是同一個(gè)對(duì)象*同一個(gè)對(duì)象的，hashCode值一定相同 **-------------------------------------------------------------------------------*普通對(duì)象的HashCode值源碼解釋：*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 *java.lang.Object.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 hash tables. *-------------------------------------------------------------------------------**/ public class Test {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}public Test() {super();}public Test(String name) {super();this.name = name;}public static void main(String[] args) {System.out.println("--------------------普通對(duì)象-----------------------");Test test3=new Test();Test test4=new Test();System.out.println(test3.hashCode());//2018699554System.out.println(test4.hashCode());//1311053135Test test=new Test("我");Test test2=new Test("我");System.out.println(test.hashCode());//366712642System.out.println(test2.hashCode());//1829164700System.out.println("--------------------String-----------------------");String s1="abc";String s2="abc";System.out.println(s1.hashCode());//96354System.out.println(s2.hashCode());//96354String s5=new String("abc");String s6=new String("abc");System.out.println(s5.hashCode());//96354System.out.println(s6.hashCode());//96354String s3=new String();String s4=new String();System.out.println(s3.hashCode());//0System.out.println(s4.hashCode());//0/*** 數(shù)值型原始類(lèi)型對(duì)應(yīng)的包裝類(lèi)(Byte,Short,Integer,Float,Double)，hashCode算法都是基于* 對(duì)應(yīng)的原始數(shù)據(jù)類(lèi)型，所以只要包裝類(lèi)的數(shù)值相同，那么hashCode必然相同* * Double類(lèi)關(guān)于hashCode源碼說(shuō)明：* Double類(lèi)的hashCode是根據(jù)對(duì)應(yīng)的double值計(jì)算獲得的。* * Returns a hash code for a {@code double} value; compatible with* {@code Double.hashCode()}.** @param value the value to hash* @return a hash code value for a {@code double} value.* @since 1.8*//*Double類(lèi)關(guān)于hashCode源碼：* public static int hashCode(double value) {long bits = doubleToLongBits(value);return (int)(bits ^ (bits >>> 32));}*/System.out.println("--------------------原始類(lèi)型對(duì)應(yīng)的包裝類(lèi)-----------------------");Double d1=5.0;Double d2=5.0;System.out.println(d1.hashCode());//1075052544System.out.println(d2.hashCode());//1075052544Double d3=new Double(5.0);Double d4=new Double(5.0);System.out.println(d3.hashCode());//1075052544System.out.println(d4.hashCode());//1075052544} }

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