Question

我想按dateLastContact比较两个“收件人”，如果相同，则按地址比较。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;
    }
}

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)

我尝试了很多事情，但是现在，我不知道该怎么办。你能帮我吗？

收件人类：

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

您违反比较方法的约定，您的关系不是可传递的。 “实施者必须确保所有sgn(compare(x, y)) == -sgn(compare(y, x))和x的{{1}}”

考虑一下：

原因是由于以下代码：

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.
}

您可能应该为第二个条件返回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 }。

合同如下：

1

比较其两个参数的顺序。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int compare(T o1, T o2):指定数学符号函数，该函数定义为根据表达式的值是否返回sgn(expression)，-1或0中的一个是负数，零或正数。

实施者必须确保所有1和sgn(compare(x, y)) == -sgn(compare(y, x))的{{1}}。（这意味着x仅在y引发异常时才必须引发异常。）

实施者还必须确保该关系是可传递的：compare(x, y)暗含compare(y, x)。

最后，实现者必须确保((compare(x, y) > 0) && (compare(y, z) > 0))对所有compare(x, z) > 0都暗示compare(x, y) == 0。

通常是这种情况，但并非严格要求sgn(compare(x, z)) == sgn(compare(y, z))。一般而言，任何违反此条件的比较器都应明确指出这一事实。推荐的语言是“注意：此比较器强加与等号不一致的顺序。”

Answer 2

一个明显的原因是：

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

o1.isDateLastContactNull()是true xor o2.isDateLastContactNull()是true
然后o1 < o2。
你是说：

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

compareTo比较方法违反了其一般合同

2 个答案: