java 如何按顺序对HashSet()函数数据进行排序？
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How to sort HashSet() function data in sequence?
提问by vincent low
I am new to Java, the function I would like to perform is to load a series of data from a file, into my hashSet() function.
我是 Java 新手，我想要执行的功能是将文件中的一系列数据加载到我的 hashSet() 函数中。
the problem is, I able to enter all the data in sequence, but I can't retrieve it out in sequence base on the account name in the file.
问题是，我可以按顺序输入所有数据，但无法根据文件中的帐户名称按顺序检索它。
Can anyone help?
任何人都可以帮忙吗？
below is my code:
下面是我的代码：
public Set retrieveHistory(){ Set dataGroup = new HashSet(); try{
公共设置检索历史（）{ 设置数据组 = 新哈希集（）；尝试{
File file = new File("C:\Documents and Settings\vincent\My Documents\NetBeansProjects\vincenttesting\src\vincenttesting\vincenthistory.txt");
BufferedReader br = new BufferedReader(new FileReader(file));
String data = br.readLine();
while(data != null){
System.out.println("This is all the record:"+data);
Customer cust = new Customer();
//break the data based on the ,
String array[] = data.split(",");
cust.setCustomerName(array[0]);
cust.setpassword(array[1]);
cust.setlocation(array[2]);
cust.setday(array[3]);
cust.setmonth(array[4]);
cust.setyear(array[5]);
cust.setAmount(Double.parseDouble(array[6]));
cust.settransaction(Double.parseDouble(array[7]));
dataGroup.add(cust);
//then proced to read next customer.
data = br.readLine();
}
br.close();
}catch(Exception e){
System.out.println("error" +e);
}
return dataGroup;
}
public static void main(String[] args) {
FileReadDataModel fr = new FileReadDataModel();
Set customerGroup = fr.retrieveHistory();
System.out.println(e);
for(Object obj : customerGroup){
Customer cust = (Customer)obj;
System.out.println("Cust name :" +cust.getCustomerName());
System.out.println("Cust amount :" +cust.getAmount());
}
回答by zellio
Directly from the HashSetclass javadoc
直接来自HashSet类 javadoc
This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.
这个类实现了 Set 接口，由一个哈希表（实际上是一个 HashMap 实例）支持。它不保证集合的迭代顺序；特别是，它不保证订单会随着时间的推移保持不变。此类允许空元素。
If you are using this class there is no way to guarantee order. You will need to introduce another data structure in order to do this. Such as ArrayListor LinkedHashSet.
如果您使用此类，则无法保证顺序。为此，您需要引入另一种数据结构。例如ArrayList或LinkedHashSet。
回答by Ran Biron
java.util.Set is a unique (element may appear only once), non-ordered, hash-based (objects must fulfill the Object.hashCode() contract) collection.
java.util.Set 是一个唯一的（元素可能只出现一次）、无序的、基于哈希的（对象必须满足 Object.hashCode() 契约）集合。
You probably want an ordered collection. LinkedHashSet is a unique, ordered (by insertion order), hash based collection.
你可能想要一个有序的集合。LinkedHashSet 是一个唯一的、有序的（按插入顺序）、基于散列的集合。
