SCJP題庫第200題
Given:
11. public class Person{
12. private String name;
13. public Person(String name){
14. this.name = name;
15. }
16. public boolean equals(Object o){
17. if(!(o instanceof Person)) return false;
18. Person p = (Person)o;
19. return p.name.equals(this.name);
20. }
21. }
Which statement is true?
A. Compilation fails because the hashCode method is not overridden.
B. A HashSet could contain multiple Person objects with the same name.
C. All Person objects will have the same hash code because the hashCode method is not overridden.
D. If a HashSet contains more than one Person object with name="Fred", then removing another Person, also with name="Fred", will remove them all.
Ans: B
解說:
B. A HashSet could contain multiple Person objects with the same name.
HashSet不會有重複的元素，但前題類別必須重寫hashCode與equals提供元素間的比較方法
Person類別只提供equals方法，沒有提供hashCode方法…
二個物件會先用hashCode()方法傳回的值是否相同，如果相同，則再使用equals()方法比較，如果兩者都相同，則視為相同的物件。
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