Java习题(6)

下列哪个声明是正确的覆盖了父类的change方法？(D) A. protected void change(int x){} B.public void change(int x, int y){} C.public void change(String s){} D.public void change(int x){}

78. 在子类中调用父类中被覆盖的方法时需要使用哪项关键字？(B) A. this B.super C.new

D.以上都不是

79. public class Employee{ private String name;

public Employee(String name){ this.name = name; }

public String getName(){ return name; } }

public class Manager extends Employee{ public Manager(String name){

System.out.println(getName()); } }

执行语句new Manager(“smith”)后程序的输出是哪项？(C) A.smith B.null

C.编译错误 D.name

80. 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？(D) A. smith B.null C.SALES D.编译错误

81. 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？(B) A.23 B.13 C.123 D.321

82. 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){ this();

System.out.print(3); } }

执行new Dog(“棕熊”);后程序输出是哪项？(A) A.143 B.423 C.243 D.1134

83 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？(A) A. smith,SALES B.null,SALES C.smith,null D.null,null ;编译错误

84. Java语言中常量的定义是哪项？(B) A. public static B.public static final C.final

D.public static abstract

85. 为了使得System.out.println()输出对象引用的时候得到有意义的信息，我们应该覆盖Object中的哪个方法？(C)

A. equals B.hashCode C.toString D.notify

86. class MyDate{ private int year; private int month;

private int day;

public MyDate(int year,int month,int day){ this.year=year;

this.month=month; this.day=day; }

//Override Method }

为了让new MyDate(1980,11,9)==new MyDate(1980,11,9) 返回true，必须在Override Method处覆盖哪个方法？(B)

A. hashCode B.equals C.toString D.notify

87. 表达式”hello” instanceof String返回的值是哪项？(A) A. true B.false C.1 D.0 E.hello

88. 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？(B) A. 京巴 B.京巴 Dog

C.null

D.Dog京巴

89. 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？(C) 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 90 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？(C) A. Pet Pet Pet B.Cat Cat Cat C.Cat Dog Pet D.Cat Dog Dog E.Pet Dog Pet 91. 现有： 2. class Cat {

3. Cat(int c) { System.out.print(“cat“ + c + “ “); } 4. }

5. class SubCat extends Cat {

6. SubCat(int c) { super(5); System.out.print(“cable “); } 7. SubCat() { this(4); }

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