compareTo比较方法违反了其一般约定

Question

我想通过dateLastContact比较两个“收件人”，如果相同，就通过地址进行比较。这是我的代码:

public class RecipientComparator implements Comparator<Recipient> {
    @Override
    public int compare(Recipient o1, Recipient o2) {
        if (o1.isDateLastContactNull() || o2.isDateLastContactNull()) {
            if (o1.isDateLastContactNull() && o2.isDateLastContactNull()) {
                return o1.getAddress().compareTo(o2.getAddress());
            } else if (o1.isDateLastContactNull()) {
                return -1;
            } else if (o2.isDateLastContactNull()) {
                return -1;
            }
        } else {
            if (o1.getDateLastContact().equals(o2.getDateLastContact())) {
                return o1.getAddress().compareTo(o2.getAddress());
            } else
                return o1.getDateLastContact().compareTo(o2.getDateLastContact());
        }
        return 0;
    }
}

而且我总是有这个错误：

Exception in thread "main" java.lang.IllegalArgumentException: Comparison method violates its general contract!
    at java.util.TimSort.mergeHi(TimSort.java:899)
    at java.util.TimSort.mergeAt(TimSort.java:516)
    at java.util.TimSort.mergeCollapse(TimSort.java:439)
    at java.util.TimSort.sort(TimSort.java:245)
    at java.util.Arrays.sort(Arrays.java:1512)
    at java.util.ArrayList.sort(ArrayList.java:1462)
    at managers.RecipientManager.getAllRecipientFromAPI(RecipientManager.java:28)
    at com.company.Main.main(Main.java:18)

我尝试了很多方法，但是现在，我不知道该怎么办。你能帮我吗？

收件人类别：

package recipientPackage;

import paramPackage.Param;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Recipient {
    private String recipientID;
    private String address;
    private String status;
    private int contactCount;
    private Date dateLastContact;
    Param param;
    private String[] attributes = {"recipientID", "address", "status", "contactCount", "dateLastContact"};

    Recipient(String[] recipientBrut, boolean isComeFromMailing) {
        if (isComeFromMailing) {
            createRecipientMailing(recipientBrut);
        } else {
            createRecipientSurvey(recipientBrut);
        }
    }

    public void createRecipientMailing(String[] recipientBrut) {
        this.setRecipientID(recipientBrut[0].substring(recipientBrut[0].indexOf(':') + 1).replaceAll("\"", ""));
        this.setAddress(recipientBrut[1].substring(recipientBrut[1].indexOf(':') + 1).replaceAll("\"", ""));
        this.setStatus(recipientBrut[3].substring(recipientBrut[3].indexOf(':') + 1).replaceAll("\"", ""));

        try {
            this.setDateLastContactForMailing(recipientBrut[5].substring(recipientBrut[5].indexOf(':') + 1).replaceAll("\"", ""));
            this.setContactCount(Integer.parseInt(recipientBrut[4].substring(recipientBrut[4].indexOf(':') + 1).replaceAll("\"", "")));
        } catch (IndexOutOfBoundsException e) {
            this.setDateLastContactForMailing(null);
        }catch (NumberFormatException e){
            e.printStackTrace();
        }
    }

    public void createRecipientSurvey(String[] recipientBrut) {
        setAddress(recipientBrut[0]);
        setStatus(recipientBrut[1]);
        setDateLastContactForSurvey(recipientBrut[2]);
        param.setParam_point_collecte(recipientBrut[5]);
        param.setParam_langue(recipientBrut[6]);
        param.setParam_semaine(recipientBrut[7]);
        param.setParam_periode(recipientBrut[8]);
        param.setParam_envoi(recipientBrut[9]);
        param.setParam_type_visiteur(recipientBrut[10]);
        param.setParam_saison(recipientBrut[11]);
    }

    private void setDateLastContactForMailing(String dateLastContact) {
        if (dateLastContact != null) {
            SimpleDateFormat formatter = new SimpleDateFormat("yyy-MM-dd'T'HH:mm:ss");
            try {
                this.dateLastContact = formatter.parse(dateLastContact);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        } else
            this.dateLastContact = null;

    }

    private void setDateLastContactForSurvey(String dateLastContact) {
        if (!dateLastContact.equals("")) {
            SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
            try {
                this.dateLastContact = formatter.parse(dateLastContact);
            } catch (ParseException ignored) {
            }
        } else
            this.dateLastContact = null;

    }
    public Boolean isDateLastContactNull() {
        return (dateLastContact == null);
    }

    public String getRecipientID() {
        return recipientID;
    }

    public void setRecipientID(String recipientID) {
        this.recipientID = recipientID;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public int getContactCount() {
        return contactCount;
    }

    public void setContactCount(int contactCount) {
        this.contactCount = contactCount;
    }

    public Date getDateLastContact() {
        return dateLastContact;
    }

    public void setDateLastContact(Date dateLastContact) {
        this.dateLastContact = dateLastContact;
    }

    public String[] getAttributes() {
        return attributes;
    }

    public void setAttributes(String[] attributes) {
        this.attributes = attributes;
    }
}

Answer 1

一个显而易见的原因是:

} else if (o1.isDateLastContactNull()) {
    return -1;
} else if (o2.isDateLastContactNull()) {
    return -1;
}

要么o1.isDateLastContNull（）是truexoro2.isDateLastContNull（）是true
然后o1

} else if (o1.isDateLastContactNull()) {
    return -1;
} else if (o2.isDateLastContactNull()) {
    return 1;
}

Answer 2

您违反了比较方法的契约，您的关系不是可传递的。"实现者必须确保sgns（)) == -sgns（比较（y， x））for allxandy"

考虑一下：

public static void main(String[] args){
    Recipient r1; // with isDateLastContactNull() == true;
    Recipient r2; // with isDateLastContactNull() == false;
    RecipientComparator rc = new RecipientComparator();

    System.out.println(rc.compare(r1, r2)); // -1
    System.out.println(rc.compare(r2, r1)); // -1
    // both print -1 which is not transitive.
}

原因是因为这段代码：

if (o1.isDateLastContactNull() && o2.isDateLastContactNull()) {
    // if both null, return comparison of addresses
    return o1.getAddress().compareTo(o2.getAddress());
} else if (o1.isDateLastContactNull()) {
    // if first null, return -1
    return -1;
} else if (o2.isDateLastContactNull()) {
    // if second null, also return -1 ?
    return -1; // should probably be 1 instead
}

对于第二个条件，您可能应该返回 1。

合同定义如下：

< code>int compare(T o1，T o2):

比较它的两个顺序参数。当第一个参数小于、等于或大于第二个参数时，返回负整数、零或正整数。在前面的描述中，符号< code>sgn(expression)表示数学符号函数，其被定义为根据expression的值是负、零还是正来返回< code>-1 、< code>0或< code>1之一。

实施者必须确保< code>sgn(compare(x，y)) == -sgn(compare(y，x))对于所有< code>x和< code>y。(这意味着当且仅当< code>compare(y，x)抛出异常时，< code>compare(x，y)必须抛出异常。)

实现者还必须确保关系是可传递的：（（比较（x， y）

最后，实现者必须确保对所有z进行比较（x， y）==0，这意味着sgn（比较（x， z））==sgn（比较（y， z））。

通常情况下，但不严格要求< code>(compare(x，y)= = 0)=(x . equals(y))。一般来说，任何违反这一条件的比较器都应该清楚地表明这一事实。推荐的语言是“注意:这个比较器强加的排序与equals不一致。”