Comparator 使用小结-优快云博客

本文详细介绍了 Java 中的 Comparator 接口，包括其基本概念、核心方法 compare 和 equals 的功能，以及如何通过实现该接口来自定义排序算法。此外，还提供了对自定义对象和中文字符串进行排序的具体示例。

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java.util.Comparator
１：java.util.Comparator是一个接口，只包含两个方法：
方法摘要
int
compare(To1,To2)
比较用来排序的两个参数。
boolean
equals(Objectobj)
指示是否其他对象“等于”此Comparator。
２：在JDK中对java.util.Comparator的功能的解释为：“强行对某些对象collection进行整体排序”。
具体的实现是在compare(To1,To2)方法中自定义排序算法，然后将Comparator对象（实现了java.util.Comparator接口的对象）作为一个参数传递给欲排序对象collection的某些排序方法。某些排序方法指的是能够接受java.util.Comparator参数的方法，比如：java.util.Arrays的publicstaticvoidsort(Object[]a,Comparatorc)
３：典型例程：
importjava.util.Comparator;
publicclassByWeightComparatorimplementsComparator
{
/**
*ComparetwoTrucksbyweight.CallbackforsortorTreeMap.
*effectivelyreturnsa-b;ordersbyascendingweight
*
*@parampFirstfirstobjectatobecompared
*
*@parampSecondsecondobjectbtobecompared
*
*@return+1ifa>b,0ifa=b,-1ifa<b
*/
publicfinalintcompare(ObjectpFirst,ObjectpSecond)
{
longaFirstWeight=((Truck)pFirst).weight;
longaSecondWeight=((Truck)pSecond).weight;
/*needsignumtoconvertlongtoint,(int)willnotdo!*/
returnsignum(aFirstWeight-aSecondWeight);
}//endcompare
/**
*Collapsenumberdownto+10or-1dependingonsign.
*Typicallyusedincompareroutinestocollapseadifference
*oftwolongstoanint.
*
*@paramdiffusuallyrepresentsthedifferenceoftwolong.
*
*@returnsignumofdiff,+1,0or-1.
*/
publicstaticfinalintsignum(longdiff)
{
if(diff>0)return1;
if(diff<0)return-1;
elsereturn0;
}//endsignum
}//endclassByWeight
程序来源：http://mindprod.com/jgloss/comparator.html
4：以下程序演示了如何对自定义对象进行排序：
packagemypack;
importjava.util.Arrays;
importjava.util.Comparator;
publicclassComparatorTest{
@SuppressWarnings("unchecked")
publicstaticvoidmain(String[]args){
Dogo1=newDog("dog1",1,5);
Dogo2=newDog("dog2",2,4);
Dogo3=newDog("dog3",3,3);
Dogo4=newDog("dog4",4,2);
Dogo5=newDog("dog5",5,1);
Dog[]dogs=newDog[]{o1,o4,o3,o5,o2};
System.out.println("未排序前");
for(inti=0;i<dogs.length;i++){
Dogdog=dogs[i];
System.out.println(dog.getName());
}
Arrays.sort(dogs,newByHeightComparator());
System.out.println("使用高度排序之后：");
for(inti=0;i<dogs.length;i++){
Dogdog=dogs[i];
System.out.println(dog.getName());
}
Arrays.sort(dogs,newByWeightComparator());
System.out.println("使用重量排序之后：");
for(inti=0;i<dogs.length;i++){
Dogdog=dogs[i];
System.out.println(dog.getName());
}
}
}
classDog{
privateStringname;
privateintweight;
privateintheight;
publicDog(Stringname,intweight,intheight){
this.setName(name);
this.weight=weight;
this.height=height;
}
publicintgetHeight(){
returnheight;
}
publicvoidsetHeight(intheight){
this.height=height;
}
publicintgetWeight(){
returnweight;
}
publicvoidsetWeight(intweight){
this.weight=weight;
}
publicvoidsetName(Stringname){
this.name=name;
}
publicStringgetName(){
returnname;
}
}
classByWeightComparatorimplementsComparator{
publicintcompare(ObjectfirstDog,ObjectsecondDog){
intfirstWeight=((Dog)firstDog).getWeight();
intsecondWeight=((Dog)secondDog).getWeight();
returnsignum(firstWeight-secondWeight);
}
publicstaticfinalintsignum(intdiff){
if(diff>0)
return1;
if(diff<0)
return-1;
else
return0;
}
}
classByHeightComparatorimplementsComparator{
publicintcompare(ObjectfirstDog,ObjectsecondDog){
intfirstHeight=((Dog)firstDog).getHeight();
intsecondHeight=((Dog)secondDog).getHeight();
returnsignum(firstHeight-secondHeight);
}
publicstaticfinalintsignum(intdiff){
if(diff>0)
return1;
if(diff<0)
return-1;
else
return0;
}
}
5：以下程序演示了如何对中文进行排序
packagemypack;
importjava.text.Collator;
importjava.text.RuleBasedCollator;
importjava.util.Arrays;
importjava.util.Locale;
publicclassTest{
publicstaticvoidmain(String[]args){
String[]test=newString[]{"的","波","次","啊"};
Arrays.sort(test,(RuleBasedCollator)Collator.getInstance(Locale.CHINA));
for(Stringkey:test)
System.out.println(key);
}
}