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比较器报错：Comparison method violates its general contract

2016-12-08 11:43 381 查看

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转载自：<a target="_blank" href="http://blog.csdn.net/fanzitao/article/details/8040201">http://blog.csdn.net/fanzitao/article/details/8040201</a>





Brother Zeng遇到的错误：



<a href="http://lib.csdn.net/base/javase" class="replace_word" title="Java SE知识库" target="_blank" style="color:#df3434; font-weight:bold;">Java</a>.lang.IllegalArgumentException: Comparison method violates its general contract!



网上查到一个解释：



Description: The sorting algorithm used by java.util.Arrays.sort and (indirectly) by java.util.Collections.sort has been replaced. The new sort implementation may throw an IllegalArgumentException if it detects a Comparable that violates the Comparable contract.

The previous implementation silently ignored such a situation. If the previous behavior is desired, you can use the new system property, java.util.Arrays.useLegacyMergeSort, to restore previous mergesort behavior. 





也就是说jdk 7的sort函数的实现变了，造成了这个问题，具体原因未知。



改一下系统设置，还是选择使用老版本的排序方法，在代码前面加上这么一句话：System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");



 





另外复习一下比较器，一个简单的例子：



类代码：

<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard"
title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 481px; top: 831px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_1" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf"
loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_1" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"
flashvars="id=1&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About"
title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a><a href="https://code.csdn.net/snippets/131345" target="_blank" title="在CODE上查看代码片" style="text-indent:0;"><img src="https://code.csdn.net/assets/CODE_ico.png"
width="12" height="12" alt="在CODE上查看代码片" style="position:relative;top:1px;left:2px;"></a><a href="https://code.csdn.net/snippets/131345/fork" target="_blank" title="派生到我的代码片" style="text-indent:0;"><img
src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="position:relative;top:2px;left:2px;"></a></div></div><ol start="1" class="dp-j"><li class="alt">public class Stu { </li><li class=""> public double age; </li><li
class="alt"> public String name; </li><li class=""> public Stu(String name,double age) </li><li class="alt"> { </li><li class=""> this.name = name; </li><li
class="alt"> this.age = age; </li><li class=""> } </li><li class="alt">} </li></ol><div
class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre code_snippet_id="131345" snippet_file_name="blog_20131227_1_4963908"
name="code" class="java" style="display: none;">public class Stu {
public double age;
public String name;
public Stu(String name,double age)
{
this.name = name;
this.age = age;
}

}</pre> 

<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard"
title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 481px; top: 1088px; width: 18px; height: 18px; z-index: 99;"><embed id="ZeroClipboardMovie_2" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf"
loop="false" menu="false" quality="best" bgcolor="#ffffff" width="18" height="18" name="ZeroClipboardMovie_2" align="middle" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer"
flashvars="id=2&width=18&height=18" wmode="transparent"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About"
title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a><a href="https://code.csdn.net/snippets/131345" target="_blank" title="在CODE上查看代码片" style="text-indent:0;"><img src="https://code.csdn.net/assets/CODE_ico.png"
width="12" height="12" alt="在CODE上查看代码片" style="position:relative;top:1px;left:2px;"></a><a href="https://code.csdn.net/snippets/131345/fork" target="_blank" title="派生到我的代码片" style="text-indent:0;"><img
src="https://code.csdn.net/assets/ico_fork.svg" width="12" height="12" alt="派生到我的代码片" style="position:relative;top:2px;left:2px;"></a></div></div><ol start="1" class="dp-j"><li class="alt">import java.util.Collections; </li><li
class="">import java.util.Comparator; </li><li class="alt">import java.util.List; </li><li class=""> </li><li
class="alt"> </li><li class="">public class CodeForBrotherZeng { </li><li class="alt"> </li><li
class=""> /** </li><li class="alt"> * @param args </li><li class=""> */ </li><li
class="alt"> public static void main(String[] args) { </li><li
class=""> Stu stu1=new Stu("foyd",22.1); </li><li
class="alt"> Stu stu2=new Stu("teddy",19.1); </li><li
class=""> Stu stu3=new Stu("dean",26.1); </li><li
class="alt"> Stu stu4=new Stu("lucas",19.1); </li><li
class=""> Stu stu5=new Stu("tina",26.1); </li><li
class="alt"> </li><li class=""> List<Stu> list = new ArrayList<Stu>(); </li><li
class="alt"> list.add(stu1); </li><li class=""> list.add(stu2); </li><li
class="alt"> list.add(stu3); </li><li class=""> list.add(stu4); </li><li
class="alt"> list.add(stu5); </li><li class=""> </li><li class="alt"> Comparator<Stu> comparator = new Comparator<Stu>() { </li><li class=""> public int compare(Stu p1, Stu p2) {//return必须是int，而str.age是double,所以不能直接return (p1.age-p2.age) </li><li class="alt"> if((p1.age-p2.age)<0) </li><li class=""> return -1; </li><li class="alt"> else if((p1.age-p2.age)>0) </li><li class=""> return 1; </li><li class="alt"> else return 0; </li><li class=""> } </li><li
class="alt"> }; </li><li class=""> //jdk 7sort有可能报错， </li><li
class="alt"> //加上这句话:System.setProperty("java.util.Arrays.useLegacyMergeSort", "true"); </li><li class=""> //表示，使用以前版本的sort来排序 </li><li class="alt"> Collections.sort(list,comparator); </li><li class=""> </li><li
class="alt"> for(int i=0;i<list.size();i++) </li><li
class=""> { </li><li class="alt"> System.out.println(list.get(i).age+" "+list.get(i).name); </li><li class=""> } </li><li class="alt"> </li><li
class=""> } </li><li class="alt"> </li><li class="">} </li></ol><div class="save_code tracking-ad" data-mod="popu_249"><a href="javascript:;" target="_blank"><img
src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre code_snippet_id="131345" snippet_file_name="blog_20131227_2_8311978" name="code" class="java" style="display: none;">import java.util.Collections;

import java.util.Comparator;

import java.util.List;

public class CodeForBrotherZeng {

/**
* @param args
*/
public static void main(String[] args) {
Stu stu1=new Stu("foyd",22.1);
Stu stu2=new Stu("teddy",19.1);
Stu stu3=new Stu("dean",26.1);
Stu stu4=new Stu("lucas",19.1);
Stu stu5=new Stu("tina",26.1);

List<Stu> list = new ArrayList<Stu>();
list.add(stu1);
list.add(stu2);
list.add(stu3);
list.add(stu4);
list.add(stu5);

Comparator<Stu> comparator = new Comparator<Stu>() {
public int compare(Stu p1, Stu p2) {//return必须是int，而str.age是double,所以不能直接return (p1.age-p2.age)
if((p1.age-p2.age)<0)
return -1;
else if((p1.age-p2.age)>0)
return 1;
else return 0;
}
};
//jdk 7sort有可能报错，
//加上这句话:System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");
//表示，使用以前版本的sort来排序
Collections.sort(list,comparator);

for(int i=0;i<list.size();i++)
{
System.out.println(list.get(i).age+" "+list.get(i).name);
}

}

}</pre> 

 

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