Java面向对象_常用类库api——对象比较器

概念：对两个或多个数据项进行比较，以确定他们是否相等，或确定他们之间的大小关系及排列顺序成为比较。

1.Comparable接口:

此接口强行对实现它的每个类的对象进行整体排序。这种排序被称为类的自然排序，类的compareTo方法被称为它的自然比较方法。

 public class ComparableDemo {

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Cat[] cats={new Cat("tom",4),new Cat("jack",3),new Cat("xiaohua",5)};
         Arrays.sort(cats);
         for (Cat cat : cats) {
             System.out.println(cat);
         }
     }

 }

 public class Cat implements Comparable<Cat> {
     private String name;
     private int age;

     public Cat() {
         super();
         // TODO Auto-generated constructor stub
     }
     public Cat(String name, int age) {
         super();
         this.name = name;
         this.age = age;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public int getAge() {
         return age;
     }
     public void setAge(int age) {
         this.age = age;
     }
     @Override
     public String toString() {
         return "Cat [name=" + name + ", age=" + age + "]";
     }
     //通过此方法实现对象比较
     @Override
     public int compareTo(Cat o) {
         // TODO Auto-generated method stub
         if(this.age <o.age ){//从小到大排序
             return -1;
         }else if(this.age >o.age ){
             return 1;
         }else{
         return 0;
     }
     }

 }

2.Comparator接口:（不改变类，再写一个比较类）

强行对某个对象collection进行整体排序的比较。

 public class ComparableDemo {

     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Dog[] dogs={new Dog("tom",4),new Dog("jack",3),new Dog("xiaohua",5)};
         Arrays.sort(dogs, new DogComparator());
         for (Dog dog : dogs) {
             System.out.println(dog);
         }
     }

 }

 public class Dog {
     private String name;
     private int age;
     public Dog() {
         super();
         // TODO Auto-generated constructor stub
     }
     public Dog(String name, int age) {
         super();
         this.name = name;
         this.age = age;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public int getAge() {
         return age;
     }
     public void setAge(int age) {
         this.age = age;
     }
     @Override
     public String toString() {
         return "Dog [name=" + name + ", age=" + age + "]";
     }
 }

 import java.util.Comparator;

 public class DogComparator implements Comparator<Dog>{

     @Override
     public int compare(Dog o1, Dog o2) {
         // TODO Auto-generated method stub
         if(o1.getAge()<o2.getAge()){
             return -1;
         }else if(o1.getAge()>o2.getAge()){
             return 1;
         }else{
         return 0;
     }
     }

 }