实现集合内对象的排序

有两种方法，一种是集合内的对象实现了comparable接口的compareTo；一种是在sort方法中传一个实现了compartor接口的类。

1.以String实现的compartTo方法为例：

//实现的是按字母顺序排序
public int compareTo(String anotherString) {
        int len1 = value.length;
        int len2 = anotherString.value.length;
        int lim = Math.min(len1, len2);
        char v1[] = value;
        char v2[] = anotherString.value;

        int k = 0;
        while (k < lim) {
            char c1 = v1[k];
            char c2 = v2[k];
            if (c1 != c2) {
          //返回负数代表another应该在前面；大于等于零的数表示本字符串在前面
                return c1 - c2;
            }
            k++;
        }
        return len1 - len2;
    }

2.实现一个compartor接口

class person{
    String name;
    int age;
    person(String name,int age){
        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 "person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class Collections_P {

    public static void main(String[] args){
        person p1=new person("leilei",18);
        person p2=new person("hauhua",1);
        person p3=new person("danny",1);
        ArrayList<person> persons=new ArrayList<person>();
        persons.add(p1);
        persons.add(p2);
        persons.add(p3);
        for(person person:persons){
            System.out.println(person.toString());
        }
        Collections.sort(persons, new Comparator<person>() {
            @Override
            public int compare(person o1, person o2) {
                return o1.getName().compareTo(o2.getName());
            }
        });
        for(person person:persons){
            System.out.println(person.toString());
        }
    }
}