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;
    }
    }
        
}