Java custom type Lookup as key for Hasmap

Recently, I often use some of the small details that I have seen before but have not actually realized, and I have a deep feeling (mastering a technology is not enough to look at it again, not enough for a time, and it is far from enough ...). ），

Let's go straight to the code.

Attributeresult

1  Public classAttributeresult {2 String value;3 String result;4 5      PublicAttributeresult () {6 7     }8 9      PublicAttributeresult (string value, string result) {Ten          This. Value =value; One          This. result =result; A     } -  - @Override the      Public Booleanequals (Object o) { -         if( This==o) -             return true; -         if(O = =NULL|| GetClass ()! =O.getclass ()) +             return false; -Attributeresult Attributeresult =(Attributeresult) o; +         if(Attributeresult.result = =NULL|| Attributeresult.value = =NULL) A             return false; at         if(Value.equals (Attributeresult.value) &&result.equals (attributeresult.result)) -             return true; -         return false; -     } -  - @Override in      Public inthashcode () { -         returnValue! =NULL? Value.hashcode (): 0; to     } +      Public Static voidMain (string[] args) { -Map<attributeresult, integer> valuelist =NewHashmap<attributeresult, integer>(); theValuelist.put (NewAttributeresult ("Mim", "yes"), 20); *Valuelist.put (NewAttributeresult ("Mim", "No"), 1); $Valuelist.put (NewAttributeresult ("xunying", "yes"), 60);Panax NotoginsengValuelist.put (NewAttributeresult ("xunying", "No"), 2); -Valuelist.put (NewAttributeresult ("Mini", "No"), 2); the         if(Valuelist.containskey (NewAttributeresult ("xunying", "Yes"))){ +SYSTEM.OUT.PRINTLN ("presence"); A}Else{ theValuelist.put (NewAttributeresult ("Mini", "yes"), 30); +         } -     } $  $}

The operating result must be: presence

In this case the Attributeresult class overloads the Hascode () method and the Equals () method so that the lookup exists, and if not overridden, ContainsKey () returns the inevitable false, because by default:

In HashMap , the key comparison order of lookups is:

1. Calculates the object's Hash Code , see if it exists in the table.
2. Checks Hash Code if the object in the corresponding location is equal to the current object

The first step is to use the hashCode() method, and the second step is to use the equals() method.

In these two steps, the two methods of the class are called by default in the absence of overloading, Object and in Object , Hash Code the calculation is based on the address of the object.

• Overloading is for the same hashCode() key , can get the same Hash Code , so HashMap you can navigate to our designated key .
• Overloading equals() is to HashMap show that the current object and the key object being saved are equal so that we actually get the key corresponding key-value pair.

The above summary is derived from 1190000002655085, thanks

Java custom type Lookup as key for Hasmap