引用作为参数传递时容易搞错的两个例子

//例子1：

class Value
{
 public int i = 15;
}
public class PassRefrence
{
 public static void main(String argv[])
 {
     PassRefrence t = new PassRefrence();
     t.first();
 }
 public void first()
 {
     int i = 5;
     Value v = new Value();
     v.i = 25;
     second(v, i);
     System.out.println(v.i);
 }
 public void second(Value v, int i)
 {
     i = 0;
     v.i = 20;
     Value val = new Value();
     v =  val;
     System.out.println(v.i + " " + i);
                
 }
}

class Value
{
 public int i = 15;
}
public class PassRefrence
{
 public static void main(String argv[])
 {
     PassRefrence t = new PassRefrence();
     t.first();
 }
 public void first()
 {
     int i = 5;
     Value v = new Value();
     v.i = 25;
     second(v, i);
     System.out.println(v.i);
 }
 public void second(Value v, int i)
 {
     i = 0;
     v.i = 20;
     Value val = new Value();
     v =  val;
     System.out.println(v.i + " " + i);
                
 }
}

class Value
{
 public int i = 15;
}
public class PassRefrence
{
 public static void main(String argv[])
 {
     PassRefrence t = new PassRefrence();
     t.first();
 }
 public void first()
 {
     int i = 5;
     Value v = new Value();
     v.i = 25;
     second(v, i);
     System.out.println(v.i);
 }
 public void second(Value v, int i)
 {
     i = 0;
     v.i = 20;
     Value val = new Value();
     v =  val;
     System.out.println(v.i + " " + i);
                
 }
}

输出结果为：
15 0
20
输出结果为：
15 0
20参数传到一个方法中后，在方法中对参数值的改变不会影响原来的值，对primitive和object refrence 都一样。对引用来说就是，在方法中又new 了一个对象并把该对象的引用赋给传递进来的参数，这样并不影响方法外的引用所指向的地址。
另外：
//例子2：
class Test
{
 public static void main(String [] args)
 {
         Base b = new Subclass();
         System.out.println(b.x);
         System.out.println(b.method());
      }
}
class Base
{
 int x = 2;
      int method()
 {
         return x;
      }
}
class Subclass extends Base
{
 int x = 3;
 int method()
 {
         return x;
      }
}
输出结果为：

2

3
输出结果为：

2

3     The rule for accessing methods and variables in a class hierarchy is as follows:
-the object reference is used when accessing variables (so the value of b.x is therefore 2).
-the underlying object is used when accessing methods (so the method called is actually the method defined in Subclass, and in Subclass, x = 3).
用父类或接口调用子类的覆盖方法时，根据动态绑定确定调用哪个子类的方法，但调用成员变量时，直接访问父类或接口的成员变量