Comparable&Comparator

接口

public interface Comparator<T> {
    //返回值可能为负数，零或者正数，代表的意思是第一个对象小于、等于或者大于第二个对象。
     int compare(T o1, T o2);
     boolean equals(Object obj);
    }
public interface Comparable<T> { 
    public int compareTo(T o);
}

使用

public class test {
    public static void main(String[] args) {
        List<UserInfo> list = new ArrayList<UserInfo>();
        list.add(new UserInfo(1,21,"name1"));
        list.add(new UserInfo(2,27,"name1"));
        list.add(new UserInfo(3,15,"name1"));
        list.add(new UserInfo(5,24,"name1"));
        list.add(new UserInfo(4,24,"name1"));
        //对该类排序
        Collections.sort(list);
        for(int i=0;i<list.size();i++){
            System.out.println(list.get(i));
        }
    }
}
 //需要比较的实体类自身实现Comparable接口
class UserInfo implements Comparable<UserInfo>{
    private int userid;
    private int age;
    private String name;
    public UserInfo(int userid, int age, String name) {
        this.userid = userid;
        this.age = age;
        this.name = name;
    }
    public int getUserid() {
        return userid;
    }
    public void setUserid(int userid) {
        this.userid = userid;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString(){
        return this.userid+","+this.age+","+this.name;
    }
    @Override
    public int compareTo(UserInfo o) {
        //如果年龄相同，则比较userid，也可以直接  return this.age-o.age;
        if(this.age-o.age==0){
            return this.userid-o.userid;
        }else{
            return this.age-o.age;
        }
    }
}

public class test1 {
    public static void main(String[] args) {
        List<UserInfo> list = new ArrayList<UserInfo>();
        list.add(new UserInfo(1,21,"name1"));
        list.add(new UserInfo(2,27,"name2"));
        list.add(new UserInfo(3,15,"name3"));
        list.add(new UserInfo(5,24,"name4"));
        list.add(new UserInfo(4,24,"name5"));
        //new一个比较器
        MyComparator comparator = new MyComparator();
        //对list排序
        Collections.sort(list,comparator);
        for(int i=0;i<list.size();i++){
            System.out.println(list.get(i));
        }
    }
}
//MyComparator是一个实现Comparator接口的比较器类，重写compare方法实现比较规则
class MyComparator implements Comparator<UserInfo>{
    @Override
    public int compare(UserInfo o1,UserInfo o2) {
        if(o1.getAge()-o2.getAge()==0){
            return o1.getUserid()-o2.getUserid();
        }else{
            return o1.getAge()-o2.getAge();
        }
    }
}
class UserInfo{
    private int userid;
    private int age;
    private String name;
    public UserInfo(int userid, int age, String name) {
        this.userid = userid;
        this.age = age;
        this.name = name;
    }
    public int getUserid() {
        return userid;
    }
    public void setUserid(int userid) {
        this.userid = userid;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString(){
        return this.userid+","+this.age+","+this.name;
    }
}