jAG304

Student 資料物件程式如下 :

import java.io.Serializable;

@SuppressWarnings({ "serial", "rawtypes" })
public class Student implements Serializable {
   private String name;
   private String id;
   private String address;
  
   public Student(String name,String id, String address){
       this.name=name;
       this.id=id;
       this.address=address;
   }
  
   public String getName() {
       return name;
   }
   public void setName(String name) {
       this.name = name;
   }
   public String getId() {
       return id;
   }
   public void setId(String id) {
       this.id = id;
   }
   public String getAddress() {
       return address;
   }
   public void setAddress(String address) {
       this.address = address;
   }

   public String toString(){
      return name+","+id+","+address;          
   }
  
   public boolean equals(Student x){
       return name.equals(x.name);
   }
  
   public int hashCode(){
       return name.hashCode();
   }
}

因 Student 資料物件要由 HashSet 集合物件處理, 並且還要儲存到檔案, 所以 Student 資料物件程式必須覆寫 equals() , HashCode 這二個方法, 以及宣告實作 Serializable 介面. 可是以下程式對於相同的 Student 資料物件, 一樣會收集, 請找出此問題 ?


import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class CreateMyClass {

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static void main(String[] args) {
        String [][] myclass = {
                {"Tony","123","456"},
                {"Rayn","345","890"},
                {"apple","001","65455"},
                {"apple","001","65455"}               
        };
        Set s = new HashSet();
       
        Student st=null;
        for(String[] x : myclass) {
            st = new Student(x[0],x[1],x[2]);
            s.add(st);
        }
       
        Iterator iter = s.iterator ();
        while (iter.hasNext ())
           System.out.println (iter.next ());
    }
}