京巴
京巴 Dog
null
Dog京巴
第1题:
interface Playable {
void play();
}
interface Bounceable {
void play();
}
interface Rollable extends Playable, Bounceable {
Ball ball = new Ball("PingPang");
}
class Ball implements Rollable {
private String name;
public String getName() {
return name;
}
public Ball(String name) {
this.name = name;
}
public void play() {
ball = new Ball("Football");
System.out.println(ball.getName());
}
}
这个错误不容易发现。
错。"interface Rollable extends Playable, Bounceable"没有问题。interface 可继承多个
interfaces,所以这里没错。问题出在interface Rollable 里的"Ball ball = new Ball("PingPang");"。
任何在interface 里声明的interface variable (接口变量,也可称成员变量),默认为public static
final。也就是说"Ball ball = new Ball("PingPang");"实际上是"public static final Ball ball = new
Ball("PingPang");"。在Ball 类的Play()方法中,"ball = new Ball("Football");"改变了ball 的
reference,而这里的ball 来自Rollable interface,Rollable interface 里的ball 是public static final
的,final 的object 是不能被改变reference 的。因此编译器将在"ball = new Ball("Football");"
这里显示有错。
第2题:
public class Pet{ private String name; public Pet(){ System.out.print(1); } public Pet(String name){ System.out.print(2); } } public class Dog extends Pet{ public Dog(String name){ System.out.print(3); } } 执行new Dog(“棕熊”);后程序输出是哪项?()
第3题:
如下程序的输出结果是______。
include<iostream>
using namespace std;
class Pet{
char name[10];
public:
Pet(char*nanle){strcpy(this->name,name);}
const char*getName( )const{return name;}
virtual void call( )eonst=0;
};
class Dog:public Pet{
public:
Dog(char*name):Pet(name){ }
void call( )eonst{cout<<"汪汪叫";}
};
class Cat:public Pet{
public:
Cat(char*name):Pet(name){ }
void call( )const{eout<<"喵喵叫";}
};
int main( ){
Pet*petl=new Dog("哈克"),*pet2=new Cat("吉米");
eout<<petl->getName( );petl->call( );eout<<endl;
cout<<pet2->getName( );pet2->call( );eout<<endl;
return 0;
}
第4题:
public class Pet{ private String name; public Pet(){ System.out.print(1); } public Pet(String name){ System.out.print(2); } } public class Dog extends Pet{ public Dog(){ System.out.print(4); } public Dog(String name){ super(name); System.out.print(3); } } 执行new Dog(“棕熊”);后程序输出是哪项?()
第5题:
public class Pet{ private String name; public Pet(String name){ this.name = name; } public void speak(){ System.out.print(name); } } public class Dog extends Pet{ public Dog(String name){ super(name); } public void speak(){ super.speak(); System.out.print(“ Dog ”); } } 执行代码 Pet pet = new Dog(“京巴”); pet.speak(); 后输出的内容是哪项?()
第6题:
执行以下代码后,下面哪些描述是正确的() public class Student{ private String name = “Jema”; public void setName(String name){ this.name = name; } public String getName(){ return this.name; } public static void main(String[] args){ Student s; System.out.println(s.getName()); } }
第7题:
public class Employee{ private String name; public Employee(String name){ this.name = name; } public String getName(){ return name; } } public class Manager extends Employee{ private String department; public Manager(String name,String department){ this.department = department; super(name); (应于上一行掉位置) System.out.println(getName()); } } Super的位置是否在方法的首行 执行语句new Manager(“smith”,”SALES”)后程序的输出是哪项?()
第8题:
有如下程序:
include<iostream>
using namespace std;
class Pet{
char name[10];
public:
Pet(char*name){strcpy(this->name,name);}
const char*getName()const {return name;}
virtual void call()const=0;
};
class Dog:public Pet{
public:
Dog(char*name):Pet(name){}
void call()const{cout<<"汪汪叫":}
};
class Cat:public Pet{
public:
Cat(char*name):Pet(name){}
void call()const{cout<<"喵喵叫";}
};
int main(){
Pet*pet1=new Dog("哈克"),*pet2=new Cat("吉米");
cout<<pet1->getName();pet1->call();cout<<end1;
cout<<pet2->getName();pet2->call();cout<<end1;
return 0;
}
程序的输出结果是______。
第9题:
public class Employee{ private String name; public Employee(String name){ this.name = name; } public void display(){ System.out.print(name); } } public class Manager extends Employee{ private String department; public Manager(String name,String department){ super(name); this.department = department; } public void display(){ System.out.println(super.display()+”,”+department); } } 执行语句new Manager(“smith”,”SALES”)后程序的输出是哪项?()
第10题:
public class Employee{ private String name; public Employee(String name){ this.name = name; } public String getName(){ return name; } } public class Manager extends Employee{ private String department; public Manager(String name,String department){ this.department = department; super(name); System.out.println(getName()); } } 执行语句new Manager(“smith”,”SALES”)后程序的输出是哪项?()