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单选题
现有: public class Pet( ) public class Cat extends Pet{) 执行代码 Cat c- new Cat( ); Pet p= (Pet)c; 后下列哪项是正确的?()
A

Petp=(Pet)c运行错误

B

Petp=(Pet)c编译错误

C

Petp=(Pet)c止常执行

D

以上都不对


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考题 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?() A、 23B、 1 3C、 123D、 321

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考题 public class Pet{  public void speak(){   System.out.print(“ Pet ”);  }  }   public class Cat extends Pet{  public void speak(){   System.out.print(“ Cat ”);  }  }   public class Dog extends Pet{  public void speak(){   System.out.print(“ Dog ”);  }  }   执行代码   Pet[] p = {new Cat(),new Dog(),new Pet()};   for(int i=0;i〈p.length;i++)   p[i].speak();   后输出的内容是哪项?()  A、Pet Pet PetB、Cat Cat CatC、Cat Dog PetD、Cat Dog Dog

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考题 单选题现有:   public class Pet()  public class Cat extends Pet{)      执行代码  Cat c- new Cat();      Pet p=  (Pet)c;  后下列哪项是正确的?()A  Pet p=(Pet)c运行错误B  Pet p=(Pet)c编译错误C  Pet p= (Pet)c止常执行D 以上都不对

考题 单选题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?()A  23B  13C  123D  321

考题 单选题public class Pet{  public void speak(){   System.out.print(“ Pet ”);  }  }   public class Cat extends Pet{  public void speak(){   System.out.print(“ Cat ”);  }  }   public class Dog extends Pet{  public void speak(){   System.out.print(“ Dog ”);  }  }   执行代码   Pet[] p = {new Cat(),new Dog(),new Pet()};   for(int i=0;i〈p.length;i++)   p[i].speak();   后输出的内容是哪项?()A Pet Pet PetB Cat Cat CatC Cat Dog PetD Cat Dog Dog

考题 单选题现有:  class A  {public String name="a"}  class B extends A {public String name="b"}      执行如下代码后的结果是哪项?()      A a=new B();  System.out.println(a.name);A   aB   bC 编译失败D 运行时抛出异常

考题 单选题public class Pet{}  public class Cat extends Pet{}   执行代码   Cat c = new Cat();   Pet p = (Pet)c;   下列哪项是正确的?A Pet p = (Pet)c正常执行B Pet p = (Pet)c编译错误C Pet p = (Pet)c运行错误D 以上都不对

考题 单选题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?()A  23B  1 3C  123D  321

考题 单选题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?()A  京巴B  京巴 DogC  nullD  Dog京巴

考题 单选题What produces a compiler error?()A  class A { public A(int x) {} }B  class A {} class B extends A { B() {} }C  class A { A() {} } class B { public B() {} }D  class Z { public Z(int) {} } class A extends Z {}