实现 Comparator 的比较方法超出定义行

Question

一般我将Comparator定义为 -

Comparator<Obj> comparator= new Comparator<Obj>() {
    public int compare(Obj o1, Obj o2) { 
        //implementation...
    } 
};

当Comaprator 是类成员的一部分时，它在代码格式上看起来不太好。有没有办法将Comparator 定义为Comparator<Obj> comparator= new Comparator<Obj>() 并在另一部分实现他的compare？

Answer 1

试试这个代码...

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

class HDTV {
    private int size;
    private String brand;

    public HDTV(int size, String brand) {
        this.size = size;
        this.brand = brand;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }
}

class SizeComparator implements Comparator<HDTV> {
    @Override
    public int compare(HDTV tv1, HDTV tv2) {
        int tv1Size = tv1.getSize();
        int tv2Size = tv2.getSize();

        if (tv1Size > tv2Size) {
            return 1;
        } else if (tv1Size < tv2Size) {
            return -1;
        } else {
            return 0;
        }
    }
}

public class Main {
    public static void main(String[] args) {
        HDTV tv1 = new HDTV(55, "Samsung");
        HDTV tv2 = new HDTV(60, "Sony");
        HDTV tv3 = new HDTV(42, "Panasonic");

        ArrayList<HDTV> al = new ArrayList<HDTV>();
        al.add(tv1);
        al.add(tv2);
        al.add(tv3);

        Collections.sort(al, new SizeComparator());
        for (HDTV a : al) {
            System.out.println(a.getBrand());
        }
    }
}

Answer 2

你可以有一个单独的类来实现Comparator：

public class MyComapartor implements Comparator{

    public int compare(Obj o1, Obj o2) 
        { //implementation...
        } 
}

然后在你的班级中使用它：

public class MyClass{

MyComapartor comp = new MyComapartor();

}

Answer 3

您是否尝试过使用嵌套类，例如：

public class Sample {
    public void method() {
        ObjComparator comparator = new ObjComparator();
    }
    public static class ObjComparator implements Comparator {
        public int compare(Obj o1, Obj o2) {
        }
    }
}

这是您寻求的解决方案吗？

Answer 4

只需定义一个实现Comparator 接口的class，并在该类中实现compare 方法，使用您的comparison logic：-

public class ObjComparator implements Comparator<Obj> {
    public int compare(Obj o1, Obj o2) { 
        //implementation
    }
}

然后，无论您想在哪里使用Comparator，都可以使用此类的实例。例如，在Arrays.sort：-

Obj[] yourArray = new Obj[10];
Arrays.sort(yourArray, new ObjComparator());

Answer 5

试试这个代码........

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

class Car {

    private String name;
    private String brand;
    private double cost;

    public Car(String name, String brand, double cost) {

        this.name = name;
        this.brand = brand;
        this.cost = cost;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getCost() {
        return cost;
    }

    public void setCost(double cost) {
        this.cost = cost;
    }

    public String toString() {

        return getName();
    }

}

public class Hog {

    ArrayList<Car> cars = new ArrayList<Car>();

    public void setIt() {

        cars.add(new Car("Padmini", "Fiat", 100008.00));
        cars.add(new Car("XYlo", "Mahindra", 100000.00));
        cars.add(new Car("Swift", "Maruti", 200000.00));
    }

    public void sortIt() {

        Collections.sort(cars, new NameComparator());
        System.out.println(cars);
        Collections.sort(cars, new BrandComparator());
        System.out.println(cars);
        Collections.sort(cars, new CostComparator());
        System.out.println(cars);
    }

    class NameComparator implements Comparator<Car> {

        public int compare(Car c1, Car c2) {

            return c1.getName().compareTo(c2.getName());
        }
    }

    class BrandComparator implements Comparator<Car> {

        public int compare(Car c1, Car c2) {

            return c1.getBrand().compareTo(c2.getBrand());
        }
    }

    class CostComparator implements Comparator<Car> {

        public int compare(Car c1, Car c2) {

            return new Double(c1.getCost()).compareTo(new Double(c2.getCost()));
        }
    }

    public static void main(String[] args) {

        Hog h = new Hog();

        h.setIt();
        h.sortIt();
    }

}