是的，这是作业，但我非常依赖于想要的东西。比较器类应该实现java.util.Comparator，sort（）方法的第二个参数应该是我的Comparator类的一个实例。
到目前为止，我的比较器类看起来像：
import java.util.Comparator;
public class Compare implements Comparator<Rational> {
public int compare1(int a, int b){
int z = 0;
if(a > b)
z = 1;
else if(b > a)
z = -1;
return z;
}
@Override
public int compare(Rational a, Rational b) {
// TODO Auto-generated method stub
return 0;
}
}
我有一个单独的方法来排序数组，但此方法使用compareTo（）
public static Collection<Rational> sort1(List<Rational> list){
List<Rational> sortedList1 = new ArrayList<Rational>();
for (int i=0;i < list.size();i++) { //iterating through list
Rational currentValue = list.get(i);
int pos = sortedList1.size();
for (int j=0;j<sortedList1.size();j++) {
int comparison = currentValue.compareTo(sortedList1.get(j)); //comparing
//this is the right position if the currentValue is greater or equal
//to the sorted value at this position
if(comparison > 0 || comparison == 0){
pos = j;
break;
}
}
sortedList1.add(pos, currentValue);
}
return sortedList1;
}
我应该使用此方法但使用单独的比较器类？我完全不知所措。
我的Rational类看起来像：
public class Rational实现Comparable {
private int num; // the numerator
private int den; // the denominator
// create and initialize a new Rational object
public Rational(int numerator, int denominator) {
if (denominator == 0) {
throw new RuntimeException("Denominator is zero");
}
int g = gcd(numerator, denominator);
num = numerator / g;
den = denominator / g;
}
// return string representation of (this)
public String toString() {
if (den == 1) {
return num + "";
} else {
return num + "/" + den;
}
}
// return (this * b)
public Rational times(Rational b) {
return new Rational(this.num * b.num, this.den * b.den);
}
// return (this + b)
public Rational plus(Rational b) {
int numerator = (this.num * b.den) + (this.den * b.num);
int denominator = this.den * b.den;
return new Rational(numerator, denominator);
}
// return (1 / this)
public Rational reciprocal() {
return new Rational(den, num);
}
// return (this / b)
public Rational divides(Rational b) {
return this.times(b.reciprocal());
}
/** ***********************************************************************
* Helper functions
************************************************************************ */
// return gcd(m, n)
private static int gcd(int m, int n) {
if (0 == n) {
return m;
} else {
return gcd(n, m % n);
}
}
/** ***********************************************************************
* Test client
************************************************************************ */
public static void main(String[] args) {
Rational x, y, z;
// 1/2 + 1/3 = 5/6
x = new Rational(1, 2);
y = new Rational(1, 3);
z = x.plus(y);
System.out.println(z);
// 8/9 + 1/9 = 1
x = new Rational(8, 9);
y = new Rational(1, 9);
z = x.plus(y);
System.out.println(z);
// 4/17 * 7/3 = 28/51
x = new Rational(4, 17);
y = new Rational(7, 3);
z = x.times(y);
System.out.println(z);
// 203/16957 * 9299/5887 = 17/899
x = new Rational(203, 16957);
y = new Rational(9299, 5887);
z = x.times(y);
System.out.println(z);
// 0/6 = 0
x = new Rational(0, 6);
System.out.println(x);
}
public int compareTo(final Rational a, final Rational b) {
return b.compareTo(a);
}
@Override
public int compareTo(Rational arg0) {
// TODO Auto-generated method stub
return 0;
}
}
答案 0 :(得分：4)
我会用
Collections.sort(list, RationalComparator.INSTANCE);
比较器看起来像
enum RationalComparator implements Comparator<Rational> {
INSTANCE;
public int compare(Rational a, Rational b) {
// do your comparison here
}
}
答案 1 :(得分：0)
public class MyCompare implements Comparator<Rational> {
@Override
public int compare(final Rational a, final Rational b) {
return a.compareTo(b);
}
}
然后：
Collections.sort(list, new MyCompare());
答案 2 :(得分：0)
你自己给出答案： “而sort（）方法的第二个参数应该是我的Comparator类的一个实例。” 所以第一行改为
public static Collection<Rational> sort1(List<Rational> list,final Comparator<Rational,Rational> comparator){
此参数可用于比较您的方法。
comparator.compare(...)
答案 3 :(得分：0)
试试这个：
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
class Rational{
private static int gcd(int m, int n) {
if (0 == n) return m;
else return gcd(n, m % n);
}
private int num; // the numerator
private int den; // the denominator
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public int getDen() {
return den;
}
public void setDen(int den) {
this.den = den;
}
// create and initialize a new Rational object
public Rational(int numerator, int denominator) {
if (denominator == 0) {
throw new RuntimeException("Denominator is zero");
}
int g = Rational.gcd(numerator, denominator);
num = numerator / g;
den = denominator / g;
}
// return string representation of (this)
public String toString() {
if (den == 1) { return num + ""; }
else { return num + "/" + den; }
}
// return (this * b)
public Rational times(Rational b) {
return new Rational(this.num * b.num, this.den * b.den);
}
// return (this + b)
public Rational plus(Rational b) {
int numerator = (this.num * b.den) + (this.den * b.num);
int denominator = this.den * b.den;
return new Rational(numerator, denominator);
}
// return (1 / this)
public Rational reciprocal() { return new Rational(den, num); }
// return (this / b)
public Rational divides(Rational b) {
return this.times(b.reciprocal());
}
}
class RationalComparator implements Comparator<Rational>{
@Override
public int compare(Rational r1, Rational r2) {
if (r1.getNum() / r1.getDen() == r2.getNum() / r2.getDen()){
return (0);
}
else if (r1.getNum() / r1.getDen() < r2.getNum() / r2.getDen()){
return (-1);
}
else{
return (1);
}
}
}
class UsingComparator {
public static void main(String[] args) {
Rational r1=new Rational(5, 2);
Rational r2=new Rational(1, 2);
List<Rational>rationalList=new ArrayList<Rational>();
rationalList.add(r1);
rationalList.add(r2);
System.out.println(rationalList);
Collections.sort(rationalList,new RationalComparator());
System.out.println(rationalList);
}
}