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

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17.选择题

class Demo
{
public void func()
<span style="white-space:pre">	</span>{
//位置1
<span style="white-space:pre">	</span>}
<span style="white-space:pre">	</span>class Inner{}
<span style="white-space:pre">	</span>public static void main (String [] args)
<span style="white-space:pre">	</span>{
Demo d = new Demo();
//位置2
<span style="white-space:pre">	</span>}
}

A.在位置1写new Inner(); //可以

B.在位置2写new Inner(); //不可以，主函数是静态的，如果要访问，Inner需静态

C.在位置2写newd.Inner(); //不可以，格式错误，newnew Demo().Inner

D.在位置2写newDemo.Inner(); //不对，Inner不是静态的

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18.写出程序结果

class Exc0 extends Exception{}
class Exc1 extends Exc0{}

class Demo
{
public static void main (String [] args)
{
try
{
throw new Exc1();
}
catch (Exception e)
{
System.out.println("Exception");
}
catch (Exc0 e)
{
System.out.println("Exc0");
}
}
}

结果：编译失败，多个catch的时候，父类的catch要放到后面

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19.补足代码

interface Test
{
void func();
}
class Demo
{
public static void main (String [] args)
{
//补足代码（匿名内部类）
}
void show(Test t)
{
t.func();
}
}

结果：

interface Test
{
void func();
}
class Demo
{
public static void main (String [] args)
{
//补足代码（匿名内部类）
new Demo().show(new Test(){public void func(){}});
}
void show(Test t)
{
t.func();
}
}

注意show方法不是静态的，要建立一个对象调用

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20.写出程序结果

class Test
{
public static String output = "";
public static void foo(int i)
{
try
{
if (i == 1)
throw new Exception();
output += "1";
}
catch (Exception e)
{
output += "2";
return;
}
finally
{
output += "3";
}
output += "4";
}
public static void main (String [] args)
{
foo(0);
System.out.println(output);
foo(1);
System.out.println(output);
}
}

结果：

134

13423

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21.建立一个图形接口，声明一个面积函数。圆形和矩形都实现这个接口，并得出两

个图形的面积。注：体现面向对象的特征，对数值进行判断，用异常处理，不合法的

数值要出现“这个数值是非法的”提示，并结束程序。

interface MyShape
{
void getArea();
}
class NoValueException extends RuntimeException
{
NoValueException(String msg)
{
super(msg);
}
}
class Rec implements MyShape
{
private double len,wid;
Rec(double len, double wid)
{
if (len <=0 || wid <=0)
throw new NoValueException("出现非法值");
this.len = len;
this.wid = wid;
}
public void getArea()
{
System.out.println("rectangle的面积是："+len*wid);
}
}
class Circle implements MyShape
{
private double radius;
public static final double PI = 3.14;
Circle(double radius)
{
if (radius <= 0)
throw new NoValueException("出现非法值");
this.radius = radius;
}
public void getArea()
{
System.out.println("circle的面积是："+PI*radius*radius);
}
}
class Demo
{
public static void main (String [] args)
{
Rec r = new Rec(1,3);
Circle c = new Circle(-5);
r.getArea();
c.getArea();
}
}

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22.补足compare函数内的代码，不许添加其他函数

class Circle
{
private static final double PI = 3.14;
private double radius;
public Circle(double r)
{
radius = r;
}
public static double compare(Circle[] cir)
{
//程序代码//其实就是求数组中的最大值
}
}
class Tc
{
public static void main (String [] args)
{
Circle [] cir = new Circle[3];//创建了一个类类型的数组
cir[0] = new Circle(1.0);
cir[1] = new Circle(2.0);
cir[2] = new Circle(4.0);
System.out.println("最大的半径值是："+Circle.compare(cir));
}
}

结果：

class Circle
{
private static final double PI = 3.14;
private double radius;
public Circle(double r)
{
radius = r;
}
public static double compare(Circle[] cir)
{
//程序代码//其实就是求数组中的最大值
double max = 0;
for (int i=0; i<cir.length; i++)
{
if (cir[i].radius > max)
{
max = cir[i].radius;
}
}
return max;
}
}
class Tc
{
public static void main (String [] args)
{
Circle [] cir = new Circle[3];//创建了一个类类型的数组
cir[0] = new Circle(1.0);
cir[1] = new Circle(2.0);
cir[2] = new Circle(4.0);
System.out.println("最大的半径值是："+Circle.compare(cir));
}
}

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23.写出程序结果

public class Demo
{
private static int j = 0;
private static boolean methodB(int k)
{
j += k;
return true;
}
public static void methodA(int i)
{
boolean b;
b = i < 10 | methodB(4);
b = i < 10 || methodB(8);
}
public static void main (String [] args)
{
methodA(0);
System.out.println(j);
}
}

结果：4

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24.加入我们在开发一个系统时需要对员工进行建模，员工包含3个属性：姓名、工

号以及工资。经理也是员工，除了含有员工的属性外，另外还有一个奖金属性。请使

用继承的思想设计出员工类和经理类。要求类中提供必要的方法进行属性访问。

abstract class Employee
{
private String name;
private String id;
private double wage;

Employee(String name, String id, double wage)
{
this.name = name;
this.id = id;
this.wage = wage;
}

public String getName()
{
return name;
}
public String getID()
{
return id;
}
public double getWage()
{
return wage;
}
}
class Staff extends Employee
{
Staff(String name, String id, double wage)
{
super(name, id, wage);
}
}
class Manager extends Employee
{
private double bonus;
public double getBonus()
{
return bonus;
}
Manager(String name, String id, double wage, double bonus)
{
super(name, id, wage);
this.bonus = bonus;
}
}
class Demo
{
public static void main (String [] args)
{
Staff s = new Staff("张三","0000011",10000);
Manager m = new Manager("李四","1000003",20000,10000);

System.out.println("******* 员工对象 *********");
System.out.println("姓名："+s.getName());
System.out.println("工号："+s.getID());
System.out.println("工资："+s.getWage());
System.out.println("******* 经理对象 *********");
System.out.println("姓名："+m.getName());
System.out.println("工号："+m.getID());
System.out.println("工资："+m.getWage());
System.out.println("奖金："+m.getBonus());
}
}

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25.在一个类中编写一个方法，这个方法搜索一个字符数组中是否存在某个字符，如果存在，

则返回这个字符在字符数组中第一次出现的位置（序号从0开始计算），否则，返回-1.要搜

索的字符数组和字符都以参数形式传递给该方法，如果传入的数组为null，应该抛出

IllegalArgumentException异常。在类的main方法中以各种可能出现的情况验证该方法编写

的是否正确，例如，字符不存在，字符存在，传入的数组为null等。

class Demo
{
public static void main (String [] args)
{
char[] chs = {'a','b','c','d','e','f','g','h'};

System.out.println("d:"+searchChar(chs,'d'));
System.out.println("k:"+searchChar(chs,'k'));
System.out.println("null:"+searchChar(null,'k'));
}

public static int searchChar(char[] chs, char key)throws IllegalArgumentException
{
if (chs == null)
throw new IllegalArgumentException();
for (int i=0; i<chs.length; i++)
{
if (chs[i] == key)
return i;
}
return -1;
}
}

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26.补足compare函数内的代码，不许添加其他函数

class Circle
{
private double radius;
public Circle(double r)
{
radius = r;
}
public Circle compare(Circle cir)
{
//补足代码
}
}
class TC
{
public static void main (String [] args)
{
Circle cir1 = new Circle(1.0);
Circle cir2 = new Circle(2.0);
Circle cir;
cir = cir1.compare(cir2);
if (cir1 == cir)
System.out.println("圆1的半径比较大");
else
System.out.println("圆2的半径比较大");
}
}

补后代码

class Circle
{
private double radius;
public Circle(double r)
{
radius = r;
}
public Circle compare(Circle cir)
{
//补足代码
return this.radius>cir.radius?this:cir;
}
}
class TC
{
public static void main (String [] args)
{
Circle cir1 = new Circle(1.0);
Circle cir2 = new Circle(2.0);
Circle cir;
cir = cir1.compare(cir2);
if (cir1 == cir)
System.out.println("圆1的半径比较大");
else
System.out.println("圆2的半径比较大");
}
}

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