Java基础知识（十二）基础知识面试习题

短命女 2022-02-20 03:31 352阅读 0赞

一些面试小练习

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![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 1][]

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这里 A a=new B(); 是多态，父类是接口，这个引用指向子类对象B()，

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 3][]

f.show('A')调用的show是子类中重写了的show,如果子类中没有才会去父类中找方法用，当for循环的循环条件是false时，for 就不执行了。后面都执行不到。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 4][]

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interface Inter
    {
        void show(int a,int b);
        void func();
    }
    class Demo
    {
        public static void main(String[] args)
        {
            //补足代码，调用两个函数，要求使用匿名内部类。
            Inter in = new Inter()
            { 
                public void show(int a,int b)
                {
                } 
                public void func()
                {
                }
            };
            in.show(2,3);
            in.func();
        }
    }

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 6][]

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![20190412145036877.png][]

5、内部类只能访问局部变量中被final修饰的变量。

11、

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showZi

变量不存在覆盖，是随着类走的，左边是什么类，变量值是哪个类中的。

函数存在覆盖，子类有用子类的，子类没有找父类的。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 9][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 10][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 11][]

这里输出A语句后由于抛异常被封装在了函数中所以不会编译失败。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 12][]

找的是父类中空参数构造函数，而父类定义了一个有参数的后系统默认不给加空参数构造函数了。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 13][]

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单独存在的throw后 和return后 **不能** 再写语句了，不仅仅是因为执行不到，而是会报错停止运行。但是如果这个抛错是被封装在函数中的，那么编译就会通过，因为封装在函数中并声明的异常是指“有可能发生异常”而不是一定会发生，但直接写throw 就是一定有异常。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 15][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 16][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 17][]

主函数是静态而show()方法不是静态所以不能直接调用需要new对象调用，所传参数是一个接口类型而且这个接口中只有一个方法，适合用匿名内部类来充当。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 18][]

return 语句执行之前会看一下后面有没有finally语句，如果有的话执行一下，没有就直接结束。

换言之，只要在finally中的语句都一定会被执行，连return都得给个面子。剩下其它任何语句 都没这特权，比如本例中finally后的output+="4"最后就不会执行到。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 19][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 20][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 21][]

|| 前是真，后面语句不执行了，结果是4

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 22][]

重点来了：引用数据类型中，“null”也是个值，并不会报错。要记住哦。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NodXl1ZGV4aWFvd3U_size_16_color_FFFFFF_t_70 23][]

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[20190412145036877.png]: /images/20220220/414890911c864d5c980e77979a20f174.png
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