迭代hashmap并创建独特的对象 - 试图防止重复 [英] Iterating through hashmap and creating unique objects - trying to prevent duplicates
问题描述
public int addPatron（String name ）抛出PatronException {
int i = 0;
// 1。 （Map.Entry< Integer，Patron>条目：patrons.entrySet（））{$（））中的hashmap
中不存在新名称， b $ b赞助人nameTest = entry.getValue（）;
// 2。如果我想添加的名称已经存在，我们希望抛出一个异常。
if（nameTest.getName（）== name）{
throw new PatronException（This patron already exists）;
// 3。如果该名称是唯一的，我们希望获得散列中已经存在的最大关键值（客户编号），并将其加1。
} else if（nameTest.getName（）！= name）{
Map.Entry< Integer，Patron> maxEntry = null; （Map.Entry< Integer，Patron> entryCheck：patrons.entrySet（））{
if（maxEntry == null || entryCheck.getKey（）> maxEntry.getKey（））{
maxEntry = entryCheck;
i = maxEntry.getKey（）;
i ++;
}
}
}其他{
抛出新的PatronException（某事不行！）;
}
// 4。如果在此之前一切正常，我们希望给我们提供名称和新的客户ID号码，然后使用它们创建一个新的Patron对象，然后将其添加到包含所有用户的此类的hashmap中。
赞助人newPatron =新赞助人（姓名，我）;
patrons.put（i，newPatron）;
}
返回i;
}
当我尝试运行一个简单的单元测试时，如果我成功添加
try {
testLibrary.addPatron（Dude ）;
testLibrary.addPatron（Dude）;
失败（这不应该起作用）;
测试失败，告诉我addPatron方法能够使用同一个名字两次。
@Jon Skeet：
我的Patron类看起来像这样：
public class Patron {
// attributes
private String name = null;
private int cardNumber = 0;
//操作
public Patron（String name，int cardNumber）{
this.name = name;
this.cardNumber = cardNumber;
}
public String getName（）{
return name;
}
public int getCardNumber（）{
return cardNumber;
}
}
== 来比较字符串几乎肯定是不合适的。但是，它不应该在你的测试用例中引起问题，因为你使用了相同的常量字符串两次，所以 == 应该可以工作。当然，你仍然应该修改代码来使用 equals 。 目前还不清楚 Patron 构造函数或 getName 方法做 - 这些都可能导致问题（例如，如果他们创建了 new 字符串的副本 - 这会导致你的测试失败，但通常也是不必要的）。
更令人担心的是这个评论：
// 3.如果名称是唯一的，我们希望获得最大的键值（客户编号）
//已经在散列中，增加一个。
这个注释在主循环中是。所以到那个时候，我们不知道这个名字是独一无二的 - 我们只知道它在这次迭代中与赞助人的名字不匹配。
。更令人担忧的是 - 我只是注意到了这一点 - 您也在迭代块内执行add 。在我看来，你应该有更多这样的东西：
public int addPatron（String name）throws PatronException {
int maxKey = -1; （Map.Entry< Integer，Patron> entry：patrons.entrySet（））{
if（entry.getValue（）。getName（）。equals（name））{
b $ b // TODO：考虑使用IllegalArgumentException
抛出新的PatronException（这个顾客已经存在）;
}
maxKey = Math.max（maxKey，entry.getKey（））;
}
int newKey = maxKey + 1;
赞助人newPatron =新赞助人（姓名，newKey）;
patrons.put（newKey，newPatron）;
返回newKey;
}
另外，它听起来像真的从名字到赞助人的地图，可能还有ID到赞助人地图。
I explain what I am trying to do in comments above the parts in the method:
public int addPatron(String name) throws PatronException {
int i = 0;
//1. Iterate through a hashmap, and confirm the new name I am trying to add to the record doesn't already exist in the hashmap
for (Map.Entry<Integer, Patron> entry : patrons.entrySet()) {
Patron nameTest = entry.getValue();
//2. If the name I am trying to add already exists, we want to throw an exception saying as much.
if (nameTest.getName() == name) {
throw new PatronException ("This patron already exists");
//3. If the name is unique, we want to get the largest key value (customer number) already in the hash, an increment by one.
} else if (nameTest.getName() != name) {
Map.Entry<Integer,Patron> maxEntry = null;
for(Map.Entry<Integer, Patron> entryCheck : patrons.entrySet()) {
if (maxEntry == null || entryCheck.getKey() > maxEntry.getKey()) {
maxEntry = entryCheck;
i = maxEntry.getKey();
i++;
}
}
} else {
throw new PatronException("Something's not working!");
}
//4. If everything is ok up to this point, we want to us the name and the new customer id number, and use those to create a new Patron object, which then gets added to a hashmap for this class which contains all the patrons.
Patron newPatron = new Patron(name, i);
patrons.put(i, newPatron);
}
return i;
}
When I try and run a simple unit test that will fail if I successfully add the same name for addPatron twice in a row, the test fails.
try {
testLibrary.addPatron("Dude");
testLibrary.addPatron("Dude");
fail("This shouldn't have worked");
The test fails, telling me the addPatron method is able to use the same name twice.
@Jon Skeet:
My Patron class looks like this:
public class Patron {
//attributes
private String name = null;
private int cardNumber = 0;
//operations
public Patron (String name, int cardNumber){
this.name = name;
this.cardNumber = cardNumber;
}
public String getName(){
return name;
}
public int getCardNumber(){
return cardNumber;
}
}
As others have said, the use of == for comparing strings is almost certainly inappropriate. However, it shouldn't actually have caused a problem in your test case, as you're using the same constant string twice, so == should have worked. Of course, you should still fix the code to use equals.
It's also not clear what the Patron constructor or getName methods do - either of those could cause a problem (e.g. if they create a new copy of the string - that would cause your test to fail, but would also be unnecessary usually).
What's slightly more worrying to me is this comment:
// 3. If the name is unique, we want to get the largest key value (customer number)
// already in the hash, an increment by one.
This comment is within the main loop. So by that point we don't know that the name is unique - we only know that it doesn't match the name of the patron in this iteration.
Even more worrying - and I've only just noticed this - you perform the add within the iteration block too. It seems to me that you should have something more like this:
public int addPatron(String name) throws PatronException {
int maxKey = -1;
for (Map.Entry<Integer, Patron> entry : patrons.entrySet()) {
if (entry.getValue().getName().equals(name)) {
// TODO: Consider using IllegalArgumentException
throw new PatronException("This patron already exists");
}
maxKey = Math.max(maxKey, entry.getKey());
}
int newKey = maxKey + 1;
Patron newPatron = new Patron(name, newKey);
patrons.put(newKey, newPatron);
return newKey;
}
Additionally, it sounds like really you want a map from name to patron, possibly as well as the id to patron map.
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