函数的调用，java传参是传值，基本数据传递数据的拷贝，引用传递引用的拷贝
class Test
{
 public static void change(int a, int b)
 {
  a = a + b;
  b = a - b;
  a = a - b; 
 }
 public static void change(int[] num)
 {
  num[0] = num[0] + num[1];
  num[1] = num[0] - num[1];
  num[0] = num[0] - num[1];
 }
 
 public static void main(String[] args)
 {
  change(2,1);              //传递数据的拷贝，交换失败
  int[] num = new int{1,2};
  change(num);              //传递地址的拷贝，交换成功
 }
 
 Point pt;
 System.oun.println(pt) 方法打印对象的时候，自动调用对象的toString方法，toString返回关于对象的描述字符串
 
 
 Professor p1 = new Professor("zsls", 50);
 Sdudent s1 = new Student("zhangsan", 20, p1);
 Student s2 = (Student)s1.clone();     //克隆s1
 s2.name = "lisi";
 s2.age = 21;
 s2.p1.name = "lsls";
 s2.p1.age = 51;
 System.out.println(s1.name + s1.age + s1.p1.name + s1.p1.age);
 System.out.println(s2.name + s2.age + s2.p1.name + s2.p1.age);  //s2是s1的克隆，不会修改s1的内容
 
}

class Point
{
 int a,b;
 public String toString()         //覆盖toString方法
 {
  return "x=" +x "," + "y=" + y;
 }
}

//对象的克隆，可以在传参的时候修改副本，而不修改对象本身
//克隆必须继承Cloneable接口，必须实现clone（）方法，clone方法返回值是Object
class Professor implement Cloneable
{
 String name;
 int age;
 Professor(String name, int age)
 {
  this.name = name;
  this.age = age;
 }
 public Object clone()          //方法的克隆
 {
  Object o = null;
  try
  {
   o = super.clone();
  }
  catch(CloneNotSurpportedException e)
  {
   System.out.println(e.toString());
  }
  return 0;
 }
}
class Student implement Cloneable   //克隆必须实现Cloneable接口
{
 String name;
 int age;
 Professor p;
 Student(String name, int age, Professor p)
 {
  this.name = name;
  this.age = age;
  this.p = p;
 }
 public Object clone()          //方法的克隆
 {
  Object o = null;
  try
  {
   o = super.clone();
  }
  catch(CloneNotSurpportedException e)
  {
   System.out.println(e.toString());
  }
  o.p = p.clone();         //想要克隆外部类，必须在这里声明，而且外部类也满足克隆条件
  return 0;
 }
}