黑马程序员------毕老师视频笔记第十天------面向对象（面向对象练习题上）

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1.写出程序结果

class Demo {public static void func(){try{throw new Exception();}finally{System.out.println("B");}}public static void main(String [] args){try{func();System.out.println("A");}catch (Exception e){System.out.println("C");}System.out.println("D");}}

 

结果：编译失败，func抛出了一个编译时异常，没有处理。

如果func方法上声明了异常 throws Exception

结果是：

B

C

D

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2.写出程序结果

class Test{Test(){System.out.println("Test");}}class Demo extends Test{Demo(){super();System.out.println("Demo");}public static void main (String [] args){new Demo();new Test();}}

结果：

Test

Demo

Test

考察的是子类的实例化过程

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3.写出程序结果

interface A{}class B implements A{public String func(){return "func";}}class Demo{public static void main(String [] args){A a = new B();System.out.println(a.func);}}

结果：编译失败，父类引用不能调用子类特有功能

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4.写出程序结果

class Fu{boolean show(char a){System.out.println(a);return true;}}class Demo extends Fu{public static void main (String [] args){int i = 0;Fu f = new Demo();Demo d = new Demo();for (f.show('A'); f.show('B')&&(i<2); f.show('C')){i++;d.show('D');}}boolean show(char a){System.out.println(a);return false;}}

结果：

A

B

这里有一点需要看一下，不是说静态函数只能调用静态成员吗，为什么main中可以调用show？注意了，这里main中并没有直接调用show，而是创建了对象，调用对象的成员函数show。

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5.写出程序结果

interface A{}class B implements A{public String test(){return "yes";}}class Demo{static A get(){return new B();}public static void main (String [] args){A a = get();System.out,println(a.test);}}

结果：编译失败，接口引用调用子类特有功能。

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6.写出程序结果

class Super{int i = 0;public Super(String a){System.out.println("A");i = 1;}public Super(){System.out.println("B");i += 2;}}class Demo extends Super{public Demo(String a){System.out.println("C");i = 5;}public static void main (String [] args){int i = 4;Super d = new Demo("A");System.out.println(d.i);}}

结果：

B

C

5

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7.补足代码

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，要求用匿名内部类}}

结果：

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，要求用匿名内部类Inter in = new Inter(){public void show(int a, int b){}public void func(){}};in.show(1,2);in.func();}}

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8.写出程序结果

class TD{int y = 6;class Inner{static int y = 3;void show(){System.out.println(y);}}}class TC {public static void main (String [] args){TD.Inner ti = new TD().new Inner();ti.show();}}

结果：编译失败，非静态内部类中不可以定义静态成员

内部类中如果定义了静态成员，该内部类必须被静态修饰

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9.选择题，写出错误答案错误的原因，用单行注释方式

class Demo

{

         intshow(int a, int b){return 0;}

}

下面哪些函数可以存在于Demo子类中

A. public int show(int a, int b){return 0;}//可以，覆盖

B. private int show(int a, int b){return 0;}//不可以，权限过小

C. private int show(int a, long b){return0;} //可以，相当于重载

D. public short show(int a, int b){return0;} //不可以，会出现调用不明确

E. static int show(int a, int b){return 0;}//不可以，静态只能覆盖静态

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10.写出this关键字的含义，final有哪些特点？

答：this代表本类对象，哪个对象调用this所在的函数，this就代表哪个对象

final：

1.修饰类，变量（成员变量、静态变量、局部变量），函数

2.修饰的类不可以被继承

3.修饰的函数不可以被覆盖

4.修饰的变量是一个常量，只能被赋值一次

5.局部内部类只能访问局部中final修饰的变量

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11.写出程序结果

class Fu{int num = 4;void show(){System.out.println("ShowFu");}}class Zi extends Fu{int num = 5;void show (){System.out.println("ShowZi");}}class T{public static void main (String [] args){Fu f = new Zi();Zi z = new Zi();System.out.println(f.num);System.out.println(z.num);f.show();z.show();}}

结果：

4

5

ShowZi

ShowZi

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12.补足代码

interface A{void show();}interface B{void add(int a, int b);}class C implements A,B{//补足程序代码}class D{public static void main (String [] args){C c = new C();c.add(4,2);c.show();//通过该函数打印以上两个数的和}}

答案：

interface A{void show();}interface B{void add(int a, int b);}class C implements A,B{//补足程序代码private int sum;public void show(){System.out.println(sum);}public void add(int a, int b){this.sum = a + b;}}class D{public static void main (String [] args){C c = new C();c.add(4,2);c.show();//通过该函数打印以上两个数的和}}

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13.写出程序结果

class Demo{public static void main (String [] args){try{showExce();System.out.println("A");}catch (Exception e){System.out.println("B");}finally{System.out.println("C");}System.out.println("D");}public static void showExce()throws Exception{throw new Exception();}}

结果：

B

C

D

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14.写出程序结果

class Super{int i = 0;Super(){}public Super(String s){i = 1;}}class Demo extends Super{public Demo(String s){i = 2;}public static void main (String [] args){Demo d = new Demo("yes");System.out.println(d.i);}}

结果：

2

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15.写出程序结果

class Super{public int get(){return 4;}}class Demo extends Super{public long get(){return 5;}public static void main (String [] args){Super s = new Demo();System.out.println(s.get());}}

结果：

编译失败，子父类get方法没有覆盖，调用不明确

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16.写出程序结果

class Demo{public static void func(){try{throw new Exception();System.out.println("A");}catch (Exception e){System.out.println("B");}}public static void main (String [] args){try{func();}catch (Exception e){System.out.println("C");}System.out.println("D");}}

结果：编译失败。打印字符串A的输出语句始终无法执行到的，就像return语句单独使用的时候，下面不能有语句一个道理。

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