我们知道，在Java的集合类中是有一些可复用的算法的，比如
Collections.sort()从小到大排序,Collections.min(),最小值Collections.max()最大值，
这些对于list操作来说都是非常常见的，也经常需要用到
List<String> strings = new ArrayList<String>();
strings.add("ab");
strings.add("cc");
strings.add("bc");
Collections.sort(strings);
String max =Collections.max(strings);
String min =Collections.min(strings);
System.out.println(strings);//[ab, bc, cc]
System.out.println(max);//cc
System.out.println(min);//ab
List<Integer> integers = new ArrayList<Integer>();
integers.add(2);
integers.add(1);
integers.add(3);
Collections.sort(integers);
Integer max1 =Collections.max(integers);
Integer min1 =Collections.min(integers);
System.out.println(integers);//[1, 2, 3]
System.out.println(max1);//3
System.out.println(min1);//1
那么问题就来了，例子中的String,Integer,都是可比较的元素，如果是自定义的ADT怎么办呢？或者是如何按照我们想的比大小的方式，比如这里String是字典序，Integer是升序，我想要换一种方式，怎么办呢？
这里有两种方法
1实现Comparable 排序接口,并实现public int compareTo(Object o)方法
public class UseAnimals {
public static void main(String[] args) {
List<Dog> dogs = new ArrayList<Dog>();
Dog dog1 = new Dog(1,"Mary");
Dog dog2 = new Dog(3,"Elizabeth");
Dog dog3 = new Dog(2,"Anne Boleyn");
dogs.add(dog1);
dogs.add(dog2);
dogs.add(dog3);
Collections.sort(dogs);
Dog max =Collections.max(dogs);
Dog min =Collections.min(dogs);
System.out.println(dogs);//[Mary 1, Anne Boleyn 2, Elizabeth 3]
System.out.println(max);//Elizabeth 3
System.out.println(min);//Mary 1
}
}
class Dog implements Comparable<Dog> {
int age;
String name ;
public Dog (int age,String name)
{
this.age=age;
this.name=name;
}
@Override
public int compareTo(Dog o) {
// TODO Auto-generated method stub
return (this.age>o.age)? 1:-1;
}
@Override
public String toString() {
// TODO Auto-generated method stub
return name+" "+age;
}
}
2.通过传入参数比较器Comparator来实现
public static void main(String[] args) {
List<Dog> dogs = new ArrayList<Dog>();
Dog dog1 = new Dog(1,"Mary");
Dog dog2 = new Dog(3,"Elizabeth");
Dog dog3 = new Dog(2,"Anne Boleyn");
dogs.add(dog1);
dogs.add(dog2);
dogs.add(dog3);
Comparator<Dog> cia = new Comparator<Dog>(){
@Override
public int compare(Dog o1, Dog o2) {
return o1.age - o2.age;
}
};
Collections.sort(dogs,cia);
Dog max =Collections.max(dogs);
Dog min =Collections.min(dogs);
System.out.println(dogs);//[Mary 1, Anne Boleyn 2, Elizabeth 3]
System.out.println(max);//Elizabeth 3
System.out.println(min);//Mary 1
}
当然也可以简单写成：
Collections.sort(dogs, new Comparator<Dog>() {
@Override
public int compare(Dog o1, Dog o2) {
return o1.age - o2.age;
}
});
这样就可以实现对自定义的ADT以自己想要的方式排序或者一键最大最小值了。
原文：https://www.cnblogs.com/blairwaldorf/p/9200919.html