comparable与comparator

        先来说说基本的认识&＃xff1a;comparable与comparator 两者都是接口&＃xff0c;实现的方法都是对对象进行排序。 comparable  这个词是以able结尾的&＃xff0c;说明是一种能力&＃xff0c;一种属性&＃xff0c;可参见 Serializable&＃xff0c;继承了该接口就可以实现序列化了。那么继承   comparable 并且重写compareTo方法&＃xff0c;就可以让该类的对象拥有与其他同类对象的比较能力。  这是该类对象所具备的能力。

      而comparator相当与从第三方的角度进行对对象的比较&＃xff0c;类的本身不需要继承该接口。

     那么什么情况下会需要comparator接口呢&＃xff1f;

     1.所比较的类没有继承comparable&＃xff0c;但是又需要比较的时候

     2.所比较的类没有继承comparable并且也重写了比较方法&＃xff0c;但是在业务上该比较方法不适用&＃xff0c;需要自己定制一个。

代码分析&＃xff1a;

1.comparable

  先定义一个商品类&＃xff0c;继承comparable&＃xff0c;重写compareTo方法

public class Goods implements Comparable {
private String name;
private double price;

public Goods() {

}

public Goods(String name, double price) {
this.name &＃61; name;
this.price &＃61; price;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name &＃61; name;
}

public double getPrice() {
return price;
}

public void setPrice(double price) {
this.price &＃61; price;
}

//指明商品比较大小的方式&＃xff0c;按照价格从低到高排序&＃xff0c;如果出现价格相同的&＃xff0c;再按照产品名称从低到高排序
&＃64;Override
public int compareTo(Object o) {
if(o instanceof Goods ){
Goods goods &＃61;(Goods)o;
if (this.price > goods.price) {
return 1;
}else if(this.price return -1;
}else
//return 0;
return this.name.compareTo(goods.name);
}
throw new RuntimeException("传入的数据类型不一致");
}
}


public class Demo {
public static void main(String[] args) throws ClassNotFoundException {
// TODO Auto-generated method stub

List list &＃61; new ArrayList<>();
Goods goods &＃61; new Goods("内裤", 33);
Goods goods2 &＃61; new Goods("丁字裤", 31);
Goods goods3 &＃61; new Goods("长裤", 32);
list.add(goods);
list.add(goods2);
list.add(goods3);
System.err.println(goods.compareTo(goods2));
//该方法会调用定义的比较器
Collections.sort(list);
list.stream().forEach(Element-> System.err.println(Element.getName()));
// 丁字裤、 长裤、内裤
}
}

    2.

public class Demo {
public static void main(String[] args) throws ClassNotFoundException {
// TODO Auto-generated method stub

List list &＃61; new ArrayList<>();
Goods goods &＃61; new Goods("内裤", 33);
Goods goods2 &＃61; new Goods("丁字裤", 31);
Goods goods3 &＃61; new Goods("长裤", 32);
list.add(goods);
list.add(goods2);
list.add(goods3);

Collections.sort(list, new Comparator() {
&＃64;Override
public int compare(Goods o1, Goods o2) {
// TODO Auto-generated method stub
return 0;
}
});
}
}

public class Demo {
public static void main(String[] args) throws ClassNotFoundException {
// TODO Auto-generated method stub

List list &＃61; new ArrayList<>();
Goods goods &＃61; new Goods("内裤", 33);
Goods goods2 &＃61; new Goods("丁字裤", 31);
Goods goods3 &＃61; new Goods("长裤", 32);
list.add(goods);
list.add(goods2);
list.add(goods3);

Compare compare &＃61; new Compare();
int a &＃61; compare.compare(goods, goods2);
System.err.println(a);
}
}
class Compare implements Comparator{
&＃64;Override
public int compare(Goods o1, Goods o2) {
// TODO Auto-generated method stub
if(o1.getPrice() > o2.getPrice())
return 1;
else
return 0;
}

}