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問(wèn)題描述
我可以使用此代碼中的所有簡(jiǎn)單比較器進(jìn)行排序，但不能使用ComplexComparator。我想不出如何編碼才能讓它正常工作。如有任何建議/解釋?zhuān)覀儗⒉粍俑屑ぁ?/p>
這是我的主程序：
package pkgTest;
import java.util.Arrays;
public class Main {
public static void main(String[] args) {
Student[] students = new Student[6];
students[0] = new Student("Pete", 1989, 3.6);
students[1] = new Student("Tomas", 1989, 3.9);
students[2] = new Student("Helen", 1990, 3.6);
students[3] = new Student("Steve", 1991, 3.7);
students[4] = new Student("Natalie", 1993, 3.7);
students[5] = new Student("John", 1992, 4.0);
NameComparator byName
= new NameComparator();
BirthDateComparator byBirthDate
= new BirthDateComparator();
AverageComparator byAverage
= new AverageComparator();
ComplexComparator complexSorting
= new ComplexComparator(byName,
byAverage);
System.out.println("===============");
System.out.println("Before sorting:");
System.out.println("===============");
for (Student student : students) {
System.out.println(student.getName()
+ " // " + student.getBirthDate()
+ " // " + student.getAverage());
}
Arrays.sort(students, complexSorting);
System.out.println("==============");
System.out.println("After sorting:");
System.out.println("==============");
for (Student student : students) {
System.out.println(student.getName()
+ " // " + student.getBirthDate()
+ " // " + student.getAverage());
}
}
}
以下是其余類(lèi)：
package pkgTest;
public class Student {
private String name;
private int birthDate;
private double average;
public Student(String name, int birthDate,
double average) {
this.name = name;
this.birthDate = birthDate;
this.average = average;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public int getBirthDate() {
return this.birthDate;
}
public void setBirthDate(int birthDate) {
this.birthDate = birthDate;
}
public double getAverage() {
return this.average;
}
public void setAverage(double average) {
this.average = average;
}
}
package pkgTest;
import java.util.Comparator;
public class ComplexComparator implements Comparator<Student> {
public ComplexComparator(Comparator<Student> one,
Comparator<Student> another) {
}
@Override
public int compare(Student one, Student another) {
/*This is the part that
I just couldn't figure
it out to get it work.
It has to work no matter
which 2 of the 3 comparators
I use to set the input
parameters of ComplexComparator.
I have to make it work by
modifying only this part of
the code.*/
}
}
package pkgTest;
import java.util.Comparator;
public class AverageComparator implements Comparator<Student> {
@Override
public int compare(Student one, Student another) {
if (one.getAverage()
< another.getAverage()) {
return -1;
} else if (one.getAverage()
== another.getAverage()) {
return 0;
} else {
return +1;
}
}
}
package pkgTest;
import java.util.Comparator;
public class BirthDateComparator implements Comparator<Student> {
@Override
public int compare(Student one, Student another) {
if (one.getBirthDate()
< another.getBirthDate()) {
return -1;
} else if (one.getBirthDate()
== another.getBirthDate()) {
return 0;
} else {
return +1;
}
}
}
package pkgTest;
import java.util.Comparator;
public class NameComparator implements Comparator<Student> {
@Override
public int compare(Student one, Student another) {
return one.getName().
compareToIgnoreCase(another.getName());
}
}
推薦答案
您必須修改類(lèi)ComplexComparator，至少…
import java.util.Comparator;
public class ComplexComparator implements Comparator<Student> {
private Comparator<Student> comparatorOne;
private Comparator<Student> comparatorTwo;
public ComplexComparator(Comparator<Student> one,
Comparator<Student> another) {
this.comparatorOne = one;
this.comparatorTwo = another;
}
@Override
public int compare(Student one, Student another) {
// make a first comparison using comparator one
int comparisonByOne = comparatorOne.compare(one, another);
// check if it was 0 (items equal in that attribute)
if (comparisonByOne == 0) {
// if yes, return the result of the next comparison
return comparatorTwo.compare(one, another);
} else {
// otherwise return the result of the first comparison
return comparisonByOne;
}
}
}
對(duì)于兩個(gè)以上的Comparator，您將需要List個(gè)List(或另一個(gè)重載的構(gòu)造函數(shù))和一個(gè)保持特定比較順序的循環(huán)。
編輯
對(duì)于您有關(guān)排序順序的其他要求，這可能會(huì)有所幫助：
public class ComplexComparator implements Comparator<Student> {
private Comparator<Student> comparatorOne;
private Comparator<Student> comparatorTwo;
private boolean orderOneAscending = true;
private boolean orderTwoAscending = true;
/**
* Constructor without any sort orders
* @param one a comparator
* @param another another comparator
*/
public ComplexComparator(Comparator<Student> one, Comparator<Student> another) {
this.comparatorOne = one;
this.comparatorTwo = another;
}
/**
* Constructor that provides the possibility of setting sort orders
* @param one a comparator
* @param orderOneAscending sort order for comparator one
* (true = ascending, false = descending)
* @param another another comparator
* @param orderTwoAscending sort order for comparator two
* (true = ascending, false = descending)
*/
public ComplexComparator(Comparator<Student> one, boolean orderOneAscending,
Comparator<Student> another, boolean orderTwoAscending) {
this.comparatorOne = one;
this.comparatorTwo = another;
this.orderOneAscending = orderOneAscending;
this.orderTwoAscending = orderTwoAscending;
}
@Override
public int compare(Student one, Student another) {
int comparisonByOne;
int comparisonByAnother;
if (orderOneAscending) {
/* note that your lexicographical comparison in NameComparator
returns a negative integer if the String is greater!
If you take two numerical Comparators, the order will
turn into the opposite direction! */
comparisonByOne = comparatorOne.compare(another, one);
} else {
comparisonByOne = comparatorOne.compare(one, another);
}
if (orderTwoAscending) {
comparisonByAnother = comparatorTwo.compare(one, another);
} else {
comparisonByAnother = comparatorTwo.compare(another, one);
}
if (comparisonByOne == 0) {
return comparisonByAnother;
} else {
return comparisonByOne;
}
}
}
只需玩弄這些值并嘗試進(jìn)行一些修改，即可熟悉有關(guān)比較和排序的常見(jiàn)問(wèn)題。
我希望這會(huì)對(duì)你有所幫助…
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