java抽象变量

package wangzhe.src;
abstract class A
{
abstract int min(int a,int b);
int max(int a,int b)
{
return a>b?a:b;
}
}
class B extends A
{
int min(int a,int b)
{
return a<b?a:b;
}
}

public class Example1
{
public static void main(String x[])
{
A a;
B b=new B();
int min=b.min(12, 34);
int max=b.max(12,34);
System.out.println("max="+max);
System.out.println("min="+min);
a=b;
max=a.max(12, 34);
System.out.println("max="+max);
}

}
和
class A
{

int max(int a,int b)
{
return a>b?a:b;
}
}
class B extends A
{
int min(int a,int b)
{
return a<b?a:b;
}
}

public class Example1
{
public static void main(String x[])
{
A a;
B b=new B();