https://heiybb.com/tags/java/ Recent content in Java on 予而不语 Hugo -- gohugo.io en-us Fri, 26 Oct 2018 04:39:00 +0000 https://heiybb.com/posts/hashcode/ Fri, 26 Oct 2018 04:39:00 +0000 https://heiybb.com/posts/hashcode/ import java.util.HashSet; import java.util.Set; public class HashEqualTest { public static void main(String[] args) { Set<Foo> fooSet = new HashSet<>(); Foo f1 = new Foo(1); Foo f2 = new Foo(1); Foo f3 = new Foo(1); Foo f4 = new Foo(1); fooSet.add(f1); fooSet.add(f2); fooSet.add(f3); fooSet.add(f4); System.out.println(fooSet.size()); System.out.println("Break Point"); // only the first one element will be stored } } /** * result * * the add method will check the hashCode first * when the hashCode is the same the the equals method will be call * to compare the two instance * * if the hashCode is not override then the hashCode compare return false * the equals will no be called * * override the equals method is strongly not recommended * in order to avoid some unpredictable issues * * * when override the equals method, parameter 'Object' type required * not the specific type */ class Foo { private int f; Foo(Integer x) { this.