如何在java中使用compareTo函数

Question

public class Pair<F,S> implements Comparable<Pair<F,S>> {
public F first;
public S second;

public F first() {
return first;
 }

public void setFirst(F first) {
this.first=first;
 }

 public S second() {
 return second;
 }

 public void setSecond(S second) {
 this.second=second;
  }

 public Pair(F first, S second) {
 super();
  this.first=first;
   this.second=second;
  }  

 public int hashCode() {
  return(first.hashCode()^second.hashCode());
}

  @Override
 public boolean equals(Object obj) {   
 return obj instanceof Pair && ((Pair)obj).first.equals(first) &&      (Pair)obj).second.equals(second);
   }

  public String toString() {
  return first + " / " + second;
   }

  @SuppressWarnings("unchecked")
  public int compareTo(Pair<F, S> o) throws ClassCastException{

int firstCompared = ((Comparable<F>) first).compareTo(o.first());
if(firstCompared!=0) return(firstCompared);
return(((Comparable<S>)second).compareTo(o.second()));
      }

    }

而且我有以下课程:

  public class Point{

public int x;
public int y;

Point(int x, int y){
    this.x = x;
    this.y = y;

}

public String toString(){

    return "(" + x + "," + y + ")";
  }
}

我的问题:假设我有四个点p1,p2,p3,p3.如何使用Pair类将对(p1,p2)与(p2,p3)进行比较？我如何使用compareTo函数？谢谢

Answer 1

由于Point类未实现,因此无法使用此方法Comparable<Point>.你必须先解决这个问题.实际上,您应该将F和S限制为仅实现Comparable的类.

要约束F和S,请将类声明更改为:

public class Pair<F extends Comparable<F>, S extends Comparable<S>> implements Comparable<Pair<F,S>> {

有了它,你不再需要投入compareTo:

@Override
public int compareTo(Pair<F, S> that) {
    int cmp = this.first.compareTo(that.first);
    if (cmp == 0)
        cmp = this.second.compareTo(that.second);
    return cmp;
}

在编写下面的代码时,编译器会告诉您Point必须实现的代码Comparable<Point>.

一旦你这样做,你可以:

Pair<Point, Point> pair1 = new Pair<>(p1, p2);
Pair<Point, Point> pair2 = new Pair<>(p3, p4);
int cmp = pair1.compareTo(pair2);