Question

任何人都可以解释一下，为什么我不能在另一个包的子类中访问受保护的变量？ Testp2，OtherPackage和Protection2类存储在包p2中，而Protection类存储在p1包中。 Protection2.java的System.out.println("n_pro = "+p.n_pro);显示错误

package p2;

public class Testp2
{
    public static void main(String a[])
    {
                        // instantiating the classes of p1 package...
    Protection2 ob = new Protection2();     
    OtherPackage ob2 = new OtherPackage();
    }
}

public class OtherPackage 
{
OtherPackage()
    {
    p1.Protection p = new p1.Protection();
    System.out.println("Inside SamePackage constructor.");

//  System.out.println(" n = "+p.n);                
//  System.out.println("n_pri = "+p.n_pri);

    System.out.println("n_pro = "+p.n_pro);
    System.out.println("n_pub = "+ p.n_pub);
    }
}

public class Protection2 extends p1.Protection{
    Protection2(){
    p1.Protection p = new p1.Protection();

    System.out.println("Inside SamePackage constructor.");
//  System.out.println(" n = "+p.n);                
//  System.out.println("n_pri = "+p.n_pri); 
//    System.out.println("n_pro = "+p.n_pro);   // when uncommented produces err(protected access specifier)
    System.out.println("n_pub = "+p.n_pub);
    }
}

package p1;

public class Protection{

int n = 1;
private int n_pri = 2;
protected int n_pro = 3;
public int n_pub = 4;

public Protection(){
    System.out.println("Inside base constructor.");
    System.out.println(" n = "+n);
    System.out.println("n_pri = "+n_pri);
    System.out.println("n_pro = "+n_pro);
    System.out.println("n_pub = "+n_pub);
    }
}

堆栈跟踪如下：

C：\ Users \ jaina_000 \ Desktop \ learn_java＆gt; javac p2 / Testp2.java 。\ p2 \ Protection2.java:9:error:n_pro在Protection中具有受保护的访问权限 System.out.println（＆＃34; n_pro =＆＃34; + p.n_pro）; //当取消注释时会产生错误（受保护的访问说明符） ^ 。\ p2 \ OtherPackage.java:9:error:n_pro在Protection中具有受保护的访问权限 System.out.println（＆＃34; n_pro =＆＃34; + p.n_pro）; //当没有注释时 urs err（受保护的访问说明符） ^ 2个错误

C：\用户\ jaina_000 \桌面\ learn_java＆GT;

Java中的访问修饰符（受保护的关键字）

0 个答案: