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/*class A implements Comaprable{}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)o1).compareTo((Student)o2); ((Comparable )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 { 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 { 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 )o1).compareTo((Student)o2); return ((Comparable)o1).compareTo((Student)o2); }}
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