Java之多态（动态绑定）

package jin.feng1;
 class Person{
  void print(){
  System.out.println();
 }
 //
}
public class Student extends Person
{
 public void sst(){}
 public static void main(String[] args)
 {
  Person p1=new Student();
  p1.sst(); //编译错误，不能访问
  p1.print();
 }
}

class Person{
  void print(){System.out.println(" person");}
void sst(){}
}
 class Person1 extends Person{
  void print(){System.out.println(" person1");}
 }
 class Person2 extends Person{
  void print(){System.out.println(" person2");}
 }
public class Student
{
 static void tune(Person p1){
  p1.print();//子类覆盖，则根据具体类型调用具体方法
 }
 public static void main(String[] args)
 {
  Person p1=new Person1();//p1是基类Person类型，它可选的调用的子类没有覆盖方法sst()和子类覆盖的方法print()
p1.sst();//子类没有覆盖，则直接调用基类
Person p2=new Person2(); 

  tune(p1); tune(p2);//
 }
}

public class Student{
 private void print(){System.out.println(" Student");}
 public static void main(String[] args)
 {
  Student p1=new Student1();
  p1.print();//貌似是动态绑定，其实调用的是自己类中的private方法。
 }
}
 class Student1 extends Student
{
  void print(){System.out.println(" Student1");}
}
//output
Student
缺陷2：成员变量和静态方法
package jin.feng1;
class Super{
 int field=0;
 int getField(){return field;}
}
class Sub extends Super{
int field=1;
int getField(){return field;}
int getSuperField(){return super.field;}
}
public class Student{
 
 public static void main(String[] args)
 {
  Super super1=new Sub();
  System.out.println("成员变量访问："+super1.field+"方法访问："+super1.getField());
  Sub sub1=new Sub();
  System.out.println(sub1.getField()+"  "+sub1.getSuperField());
 }
}

package jin.feng1;
class Static1{
 static void print(){System.out.println("Static1 method");}
 void ss(){System.out.println("normal1 method");}
}
class Static2 extends Static1{
 static void print(){System.out.println("Static2 method");}
 void ss(){System.out.println("normal2 method");}
}
public class StaticDynmic
{
public static void main(String args[]){
 Static1 static1=new Static2();
 static1.print();
 static1.ss();
}
}

package jin.feng1; 
class Constructor11{ 
 void draw(){System.out.println(" Constructor11 draw()");} 
  
 public Constructor11(){ 
  System.out.println("Constructor11:before draw()"); 
  draw(); 
  System.out.println("Constructor11:after draw()"); 
 } 
} 
class Constructor12 extends Constructor11{ 
 private int radius=2; 
 public Constructor12(){ 
  System.out.println("Constructor12:before draw()"); 
  draw(); 
  System.out.println("Constructor12:after draw()"); 
 } 
 void draw() 
 { 
  System.out.println("Constructor12+draw "+radius); 
 } 
} 
public class Constuctor22 
{ 
 public static void main(String[] args) 
 { 
  new Constructor12(); 
 } 
}