Ikk：新頁面: Given:
11. public class Person{
12. private String name;
13. public Person(String name){
14. &n...

2013-03-27T17:05:53Z

新頁面: Given: 11. public class Person{ 12. private String name; 13. public Person(String name){ 14. &n...

新頁面

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.

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解答

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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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{{SCJP 1.6版考題講解}}

SCJP 1.6版考題 200 - 修訂歷史

Ikk：新頁面: Given: 11. public class Person{ 12. private String name; 13. public Person(String name){ 14. &n...

Ikk：新頁面: Given:
11. public class Person{
12. private String name;
13. public Person(String name){
14. &n...