[英]Strange behaviour: Java Comparator randomizes list entries
I'm curious. 我很好奇。 What could be the reason that a Comparator shuffles entries on each application start? 可能是比较器在每个应用程序启动时随机播放条目的原因是什么?
final static class ContactsListComparator implements Comparator
{
public int compare(Object o1, Object o2)
{
if((o1.toString().compareTo(o2.toString()))<0)
{
return -1;
}
if((o1.toString().compareTo(o2.toString()))>0)
{
return 1;
}
else
{
return 0;
}
}
}
First App Start: 首次应用开始:
Second App Start 第二个App Start
As mentioned in one the answer 如答案所述
The Comparator actually compares an custom object Contact 比较器实际上比较了自定义对象Contact
public class Contact
{
// Members
private String _contactFirstName;
private String _contactLastName;
private long _contactLastModified;
// Constructor
public Contact()
{
set_contactLastModified();
}
public Contact(String contactFirstName)
{
_contactFirstName = contactFirstName;
set_contactLastModified();
}
// Accessable Getters
public String get_contactFirstName()
{
return _contactFirstName;
}
public String get_contactLastName()
{
return _contactLastName;
}
public long get_contactLastModified()
{
return _contactLastModified;
}
public void set_contactLastModified()
{
_contactLastModified = System.currentTimeMillis();
}
}
your toString method probably isn't overridden for your objects representing the contacts. 您的toString方法可能不会覆盖表示联系人的对象。 It will return a hash string for those objects, which varies every time your app is run. 它将返回这些对象的哈希字符串,每次运行应用程序时都会有所不同。
You can fix this either of two ways: 您可以通过以下两种方式解决此问题:
toString()
method in your Contact
object to return the contact's name (1), or 覆盖Contact
对象中的toString()
方法以返回联系人的姓名(1)或 Comparator
to Comparator<Contact>
so it gets Contact
objects as parameters (2) 将Comparator
更改为Comparator<Contact>
以便将Contact
对象作为参数获取(2) for (1), add this to your Contact class: 对于(1),将其添加到您的Contact类:
@Override public String toString() {
return get_contactFirstName();
}
for (2) you would end up with this Comparator implementation: 对于(2)你最终会得到这个比较器的实现:
final static class ContactsListComparator implements Comparator<Contact> {
public int compare(Contact o1, Contact o2) {
return contact1.get_contactFirstName().compareTo(contact2.get_contactFirstName());
}
}
you don't even need to check for the <0 or >0, but you can just return whatever the String comparison gives. 你甚至不需要检查<0或> 0,但你可以返回字符串比较给出的任何内容。
I would use: 我会用:
final static class ContactsListComparator implements Comparator<Contact>
{
public int compare(Contact c1,Contact c2)
{
int i=c1.get_contactLastName().compareTo(c2.get_contactLastName());
if(i!=0) return i;
return c1.get_contactFirstName().compareTo(c2.get_contactFirstName());;
}
}
Your first example is basically the same as 你的第一个例子与...基本相同
final static class ContactsListComparator implements Comparator {
public int compare(Object o1, Object o2) {
return o1.toString().compareTo(o2.toString());
}
}
This would work if you override toString() like 如果你重写toString()就行了
public String toString() {
return _contactFirstName + ' ' + _contactLastName;
}
However, a comparator which compares the intended fields is better as has been suggested. 然而,如所建议的那样,比较预期场的比较器更好。
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