Java.lang.object has two very important methods defined: public boolean equals(Object obj) and public int hashCode().equals() methodIn java equals() method is used to compare equality of two Objects. The equality can be compared in two ways:...
* method whenever this method is overridden, so as to maintain the * general contract for the {@code hashCode} method, which states * that equal objects must have equal hash codes. 需要注意的是,一般来说,如果重写了equals方法,都必须要重写hashcode方法, 来确保具有相同引用的对象,能够具有同样的has...
/*** 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 ...
We are missing the second important methodhashCode(). As java docs say, if we overrideequals()then wemustoverridehashCode(). So let’s add another method in ourEmployeeclass. @OverridepublicinthashCode(){finalintPRIME=31;intresult=1;result=PRIME*result+getId();returnresult;} Once the above m...
This is what the JDK 1.4 API documentation says about the hashCode method of Object class- 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...
上面的三步也是<Effective Java>中推荐的步骤,基本可保证万无一失. 如何重写hashCode()方法 在JavaSE 7 Specification中指出, "Note that it is generally necessary to override the hashCode method whenever this method(equals) is overridden, so as to maintain the general contract for the hashCode method,...
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: ...
Ifo1.equals(o2), theno1.hashCode() == o2.hashCode()should always betrue. Ifo1.hashCode() == o2.hashCodewill be. When to override equals() and hashCode() methods? When we override equals() method, it’s almost necessary to override the hashCode() method too so that their contract is...
今天看了Object的equals() and hashCode() method, 做下笔记 equals() method 需要遵守的条件: Reflexive(反射性): X.equals(X) == true, 自身equals Symmetric(对称性): 如果X.equals(Y), 那么Y.equals(X). Transitive(传递性): 如果X.equals(Y) 且Y.equals(Z) , 那么X.equals(Z). ...
Null returns false“All objects must be unequal to null.”This last rule is what Josh Bloch, author ofEffective Java, calls “Non-nullity”. When given a null as an equals method parameter, we should always return false and never throw aNullPointerException. ...