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/*class A implements Comaprable<A>{}那么 A x = new A(); 类关系图Object o = A; ObjectComparable c = A; | ComparableA 实现了 Comparable 接口嘛 |-----|-----A所以有 o instanceof A == true; o instanceof Comparable == true;
例如ArrayList添加对象实例时，对象实例添加之后先向上转型为Object！内部用Object[]数组接收！
Arrays.sort()对Object排序的函数内部就是将 Object 向下转型为Comparable类型。
因为每个对象实现了Comparable接口，利用多态性，(Comparable)o1).compareTo(o2)将调用子类的compareTo()方法！
((Comparable<Object>)o1).compareTo((Student)o2);
((Comparable<XXX>)o1).compareTo((YYY)o2);
如果想写泛型那么 XXX 要么是同一类型，要么XXX是YYY的父类！因为我们强转的Comparable是比较XXX类型数据的，
而YYY类型满足上面的条件才能成功向上转型为XXX类型！
*/class Person implements Comparable<Person>{
String name;
int age;
Person(){
name = "";
age = 0;
}
Person(String name, int age){
this.name = name;
this.age = age;
}
public String toString(){
return name + "...." + age;
}
public boolean equals(Object o){
Person x = (Person)o;
return name.equals(x.name) && age==x.age;
}
public int compareTo(Person o){
if(name.compareTo(o.name)==0)
return o.age - age;
return o.name.compareTo(name);
}
}class Student implements Comparable<Student>{
String name;
int age;
public Student(){
name = "";
age = 0;
}
public Student(String name, int age){
this.name = name;
this.age = age;
}
public int compareTo(Student o){
if(name.compareTo(o.name)==0)
return o.age - age;
return o.name.compareTo(name);
}
} public class Test{
public static void main(String[] args){
Person p = new Person("fsf", 45);
Student s = new Student("faga", 20);
Student ss = new Student("fsfdfsf", 456);
Comparable xx = (Comparable)s;
System.out.println(xx);
cmp(s,ss);
}
public static int cmp(Object o1, Object o2){
//return ((Comparable<Object>)o1).compareTo((Student)o2);
return ((Comparable)o1).compareTo((Student)o2);
}
} |
本文转自 小眼儿 博客园博客，原文链接：http://www.cnblogs.com/hujunzheng/p/3871930.html，如需转载请自行联系原作者