class Dog { } class Harrier extends Dog { } class DogTest { public static void main(String [] args) { Dog d1 = new Dog(); Harrier h1 = new Harrier(); Dog d2 = h1; Harrier h2 = (Harrier) d2; Harrier h3 = d2; } } 下面哪一项是正确的?()
第1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2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3题:
A.编译失败
B.2个Dog对象被创建
C.2个Harrier对象被创建
D.3个Harrier对象被创建
第4题:
class Animal{ Animal getOne(){return new Animal();}} class Dog extends Animal{ //insert code here } class AnimalTest{ public static void main(String[] args){ Animal[] animal={ new Animal(), new Dog()}; for(Animal a:animal){ Animal x= a.getOne(); } } } 和代码: 3a.Dog getOne() { return new Dog();} 3b.Animal getOne() { return new Dog();} 第3行中插入的哪项编译且运行无异常?
第5题:
public class Test { public enum Dogs {collie, harrier, shepherd}; public static void main(String [] args) { Dogs myDog = Dogs.shepherd; switch (myDog) { case collie: System.out.print(”collie “); case default: System.out.print(”retriever “); case harrier: System.out.print(”harrier “); } } } What is the result?()
第6题:
10. interface Jumper { public void jump(); } ...... 20. class Animal {} ...... 30. class Dog extends Animal { 31. Tail tail; 32. } ...... 40. class Beagle extends Dog implements Jumper { 41. public void jump() { } 42. } ....... 50. class Cat implements Jumper { 51. public void jump() { } 52. } Which three are true?()
第7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8题:
A.2个Dog对象被创建
B.2个Harrier对象被创建
C.3个Harrier对象被创建
D.编译失败
第9题:
现有: class Dog{ } class Harrier extends Dog { } class DogTest{ public static void main (String [] args) { Dog dl=new Dog(); Harrier hl=new Harrier(); Dog d2=hl; Harrier h2= (Harrier) d2; Harrier h3=d2; } } 下面哪一项是正确的?()
第10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){ //这里隐藏了一句代码:super.pet(); System.out.print(3); } } 执行new Dog(“棕熊”);后程序输出是哪项?()