小编Cha*_*nth的帖子

如果它的子节点位于不同的包中,为什么我们不能用受保护的构造函数实例化一个类？如果可以访问受保护的变量和方法,为什么同样的规则也不适用于受保护的构造函数？

PACK1:

package pack1;

public class A {
    private int a;
    protected int b;
    public int c;

    protected A() {    
        a = 10;
        b = 20;
        c = 30;
    }
}

PACK2:

package pack2;

import pack1.A;

class B extends A {
    public void test() {
        A obj = new A(); // gives compilation error; why?
        //System.out.println("print private not possible :" + a);
        System.out.println("print protected possible :" + b);
        System.out.println("print public possible :" + c);
    }
}

class C {
    public …

问:我需要对以下代码的输出进行详细说明...使用runnable接口创建的线程和通过扩展线程类直接创建的线程有什么区别... ???

Q1:

public class BalanceChecker1{
    public static void main(String [] args) {
        RunnableClass runnableClass=new RunnableClass();
        new Thread(runnableClass).start();
        new Thread(runnableClass).start();
    }
}

class RunnableClass implements Runnable{
    Bean bean=new Bean();
    public void run(){
        synchronized(bean){
            bean.incBalance();
        }
    }
}

class Bean{
    private int balance=0;
    public void incBalance(){
        balance++;
        System.out.println(" The thread name "+Thread.currentThread().getName());
        System.out.println(" The balance is "+balance);
    }
}

OUTPUT:

 The thread name Thread-0
 The balance is 1
 The thread name Thread-1
 The balance is 2

Q2:

public class BalanceChecker1{
    public …