Controlling Access to Members of a Class (protected)－roczen2007

不同package存取類別的Protected資料成員

package A;
public class Base{
   private int privateData=0;
   protected int protectedData=1;
   int packageData=2;
   public int publicData=3;

   public Base(){
   }

   public void publicMethod(){
       System.out.format("publicMethod called%n");
   }

   private void privateMethod(){
       System.out.format("privateMethod called%n");
   }

   void packageMethod(){
       System.out.format("packageMethod called%n");
   }

   protected void protectedMethod(){
       System.out.format("protectedMethod called%n");
    }
}

package B;
import A.Base;
class Subclass extends Base{
   public static void main(String[] args){
       Base b=new Base();
       //b.privateMethod();//illegal
       //b.packageMethod();//illegal
       //b.protectedMethod();//illegal
       b.publicMethod();//legal 不同package只能呼叫public成員

       //System.out.format("privateData: %2d%n",b.privateData);//illegal
       //System.out.format("packageData: %2d%n",b.packageData);//illegal
       //System.out.format("protectedData: %2d%n",b.protectedData);//illegal
       System.out.format("publicData: %2d%n",b.publicData);//legal

Subclass s=new Subclass();

        s.publicMethod();//legal
       s.protectedMethod();//legal protected資料可由他的子類別存取
       System.out.format("protectedData: %2d%n",s.protectedData);//legal
       //s.packageMethod();//illegal
       //System.out.format("packageData: %2d%n",s.packageData);//illegal 跨package不能使用package變數

        //System.out.format("privateData: %2d%n",s.privateData);//illegal private變數不能繼承


   }

}

存取權限開放的大小

public > protected > package(default) > private

class的權限如未被開啟，則裡面的資料就算是public也不能被存取。

引用自http://life.csu.edu.au/java-tut/java/javaOO/accesscontrol.html