Java教程
java考试
7-2 判断闰年
import java.util.*;
public class Main
{
public static void main(String args[])
{
Scanner input=new Scanner(System.in);
int y=input.nextInt();
if(y%400==0)System.out.println("yes");
else if(y%100==0)System.out.println("no");
else if(y%4==0)System.out.println("yes");
else System.out.println("no");
}
}
7-5 分解质因数
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int a=sc.nextInt();
int b=sc.nextInt();
for (int i = a; i <= b; i++) {
if (isPrime(i))continue;
else prime(i);
}
}
public static boolean isPrime(int n) {
boolean ret=true;
for (int i = 2; i <= Math.sqrt(n); i++) {
if (n%i==0){
ret=false;
break;
}
}
if (ret) System.out.println(n+"="+n);
return ret;
}
public static void prime(int n){
System.out.print(n+"=");
for (int i = 2; i <= n; i++) {
while (n%i==0&&n!=i){
System.out.print(i+"*");
n/=i;
}
if (i==n){
System.out.println(i);
}
}
}
}
7-6 统计最大数出现次数
import java.util.Scanner;
public class Main{
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int a;
int max=-1;
int count=1;
do {
a=sc.nextInt();
if (max<a) {
max = a;
count=1;
}
else if (max==a)count++;
}while (a!=0);
System.out.println("The largest number is "+max);
System.out.println("The occurrence count of the largest number is "+count);
}
}
7-10 jmu-Java-03面向对象基础-04-形状-继承
import java.util.Scanner;
abstract class Shape {
double PI = 3.14;
public abstract double getPerimeter();
public abstract double getArea();
}
class Rectangle extends Shape {
int wide, len;
Rectangle(int a, int b) {
wide = a;
len = b;
}
@Override
public double getPerimeter() {
// TODO Auto-generated method stub
return 2 * (wide + len);
}
@Override
public double getArea() {
// TODO Auto-generated method stub
return wide * len;
}
public String toString(){
return "[width=" + wide + ", length=" + len + "]";
}
}
class Circle extends Shape {
int radius;
Circle(int _radius) {
radius = _radius;
}
@Override
public double getPerimeter() {
// TODO Auto-generated method stub
return radius * 2 * PI;
}
@Override
public double getArea() {
// TODO Auto-generated method stub
return radius * radius * PI;
}
public String toString(){
return "[radius=" + radius + "]";
}
}
public class Main {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
in.nextLine();
Shape A[] = new Shape[n];
int k = 0, j = 0;
double sumAllArea = 0, sumAllPerimeter = 0;
for (int i = 0; i < n; i++) {
String S = in.next();
if (S.equals("rect")) {
int wide = in.nextInt(), len = in.nextInt();
in.nextLine();
A[i] = new Rectangle(wide, len);
} else if (S.equals("cir")) {
int radius = in.nextInt();
in.nextLine();
A[i] = new Circle(radius);
}
sumAllArea += A[i].getArea();
sumAllPerimeter += A[i].getPerimeter();
}
System.out.println(sumAllPerimeter);
System.out.println(sumAllArea);
System.out.print("[");
for (int i = 0; i < n; i++) {
if(i != 0)
System.out.print(", ");
if (A[i] instanceof Rectangle) {
System.out.print("Rectangle ");
System.out.print(A[i].toString());
}
else {
System.out.print("Circle ");
System.out.print(A[i].toString());
}
}
System.out.println("]");
for(int i = 0;i < n;i++) {
if(A[i] instanceof Rectangle) {
System.out.println("class Rectangle,class Shape");
}else {
System.out.println("class Circle,class Shape");
}
}
in.close();
}
}
7-11 jmu-Java-03面向对象-06-继承覆盖综合练习-Person、Student、Employee、Company (15 分)
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Scanner;
public class Main {
public static void main(String[] args) throws InterruptedException {
Scanner sc=new Scanner(System.in);
List<Person> personList=new ArrayList<Person>();
String name;
int age;
boolean gender;
String stuNo;
String clazz;
String companyName;
Company company;
double salary;
while(true) {
String t=sc.next();
if(t.equals("s")) {
name=sc.next();
age=sc.nextInt();
gender=sc.nextBoolean();
stuNo=sc.next();
clazz=sc.next();
if(name==null||stuNo==null||clazz==null) {
continue;
}
personList.add(new Student(name, age, gender, stuNo, clazz));
}else if(t.equals("e")){
name=sc.next();
age=sc.nextInt();
gender=sc.nextBoolean();
salary=sc.nextDouble();
companyName=sc.next();
company=new Company(companyName);
if(name==null) {
continue;
}
if(companyName==null) {
companyName="null";
}
personList.add(new Employee(name, age, gender, company, salary));
}else{
break;
}
}
Collections.sort(personList, new Name_AgeComparator());
for(int i=0;i<personList.size();i++) {
System.out.println(personList.get(i).toString());
}
String str=sc.next();
while(true) {
if(str.equals("return")||str.equals("exit")) {
break;
}else {
List<Person> stuList=new ArrayList<Person>();
List<Person> empList=new ArrayList<Person>();
boolean flag1=true;
boolean flag2=true;
for(int i=0;i<personList.size();i++) {
if(personList.get(i).toString().indexOf("Student")>=0) {
if(stuList.size()==0) {
stuList.add(personList.get(i));
}
for(int j=0;j<stuList.size();j++) {
if(personList.get(i).equals(stuList.get(j))){
flag1=false;
}
}
if(flag1) {
stuList.add(personList.get(i));
}
flag1=true;
}else {
if(empList.size()==0) {
empList.add(personList.get(i));
}
for(int j=0;j<empList.size();j++) {
if(personList.get(i).equals(empList.get(j))){
flag2=false;
}
}
if(flag2) {
empList.add(personList.get(i));
}
flag2=true;
}
}
System.out.println("stuList");
for(int i=0;i<stuList.size();i++) {
System.out.println(stuList.get(i).toString());
}
System.out.println("empList");
for(int i=0;i<empList.size();i++) {
System.out.println(empList.get(i).toString());
}
break;
}
}
}
static class Name_AgeComparator implements Comparator<Person>{
@Override
public int compare(Person o1, Person o2) {
if(o1.name.compareTo(o2.name)==0) {
if(o1.age==o2.age) {
return 0;
}else if(o1.age<o2.age) {
return -1;
}else {
return 1;
}
}else {
return(o1.name.compareTo(o2.name));
}
}
}
}
abstract class Person{
String name;
int age;
boolean gender;
public Person(String name, int age, boolean gender) {
super();
this.name = name;
this.age = age;
this.gender = gender;
}
@Override
public String toString() {
return this.name+'-'+String.valueOf(this.age)+'-'+String.valueOf(this.gender);
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Person other = (Person) obj;
if (age != other.age)
return false;
if (gender != other.gender)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
class Student extends Person{
String stuNo;
String clazz;
public Student(String name, int age, boolean gender, String stuNo, String clazz) {
super(name,age,gender);
this.clazz=clazz;
this.stuNo=stuNo;
}
@Override
public String toString() {
return"Student:"+ super.toString()+'-'+this.stuNo+'-'+this.clazz;
}
@Override
public boolean equals(Object obj) {
if (!super.equals(obj))
return false;
if (this == obj)
return true;
if (getClass() != obj.getClass())
return false;
Student other = (Student) obj;
if (clazz == null) {
if (other.clazz != null)
return false;
} else if (!clazz.equals(other.clazz))
return false;
if (stuNo == null) {
if (other.stuNo != null)
return false;
} else if (!stuNo.equals(other.stuNo))
return false;
return true;
}
}
class Company{
String name;
public Company(){
}
public Company(String name) {
this.name = name;
}
@Override
public String toString() {
return name;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Company other = (Company) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
class Employee extends Person{
Company company;
double salary;
public Employee(String name, int age, boolean gender, Company company, double salary) {
super(name, age, gender);
this.company = company;
this.salary = salary;
}
@Override
public String toString() {
return "Employee:"+ super.toString()+'-'+company+'-'+salary;
}
@Override
public boolean equals(Object obj) {
if (!super.equals(obj))
return false;
if (this == obj)
return true;
if (getClass() != obj.getClass())
return false;
Employee other = (Employee) obj;
if (company == null) {
if (other.company != null)
return false;
}
else if (!company.equals(other.company))
return false;
DecimalFormat df = new DecimalFormat("#.#");
if (!df.format(salary) .equals( df.format(other.salary)))
return false;
return true;
}
}
7-15 USB接口的定义
interface USB{
void work();
void stop();
}
class Mouse implements USB{
@Override
public void work() {
System.out.println("我点点点");
}
@Override
public void stop() {
System.out.println("我不能点了");
}
}
class Upan implements USB{
@Override
public void work() {
System.out.println("我存存存");
}
@Override
public void stop() {
System.out.println("我走了");
}
}
public class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
USB usb1=new Mouse();
usb1.work();
usb1.stop();
USB usbs[]=new USB[2];
usbs[0]=new Upan();
usbs[1]=new Mouse();
for(int i=0;i<usbs.length;i++) {
usbs[i].work();
usbs[i].stop();
}
}
}
7-16 jmu-Java-03面向对象基础-01-构造函数与toString
import java.util.Scanner;
class Person{
private String name = null;
private int age = 0;
private boolean gender = false;
private int id = 0;
public Person() {
System.out.println("This is constructor");
System.out.println(name+","+age+","+gender+","+id);
System.out.println("Person [name="+name+", age="+age+", gender="+gender+", id="+id+"]");
}
public Person(String n, int a, boolean g) {
this.name = n;
this.age = a;
this.gender = g;
}
public String toString() {
System.out.println("Person [name="+this.name+", age="+this.age+", gender="+this.gender+", id="+0+"]");
return name;
}
}
public class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
@SuppressWarnings("resource")
Scanner reader = new Scanner(System.in);
int number = reader.nextInt();
Person[] per = new Person[number];
for(int i=0; i<per.length; i++) {
String name = reader.next();
int age = reader.nextInt();
boolean genter = reader.nextBoolean();
per[i] = new Person(name,age,genter);
}
for(int x=per.length-1; x>=0;x--){
per[x].toString();
}
per.toString();
@SuppressWarnings("unused")
Person s = new Person();
}
}
7-17 定义商品类，封装成员变量，输出对象
import java.util.Scanner;
class stuff{
private String number;
private String name;
private double price;
public String getNumber() {
return number;
}
public void setNumber(String number) {
this.number = number;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
stuff(String number, String name,double price ) {
this.name = name;
this.number = number;
this.price = price;
}
public String toString(){
return getNumber()+","+getName()+","+getPrice();
}
}
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String number = sc.next();
String name = sc.next();
double price = sc.nextDouble();
stuff a = new stuff(number, name, price);
System.out.println(a.toString());
}
}
7-18 定义类与创建对象
public class Main {
public static void main(String[] args) {
Person p1=new Person("lili", 19);
Person p2=new Person("lucy", 20);
System.out.println("this person is "+p1.name+",her age is "+p1.age);
System.out.println("this person is "+p2.name+",her age is "+p2.age);
}
}
class Person {
String name;
int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
7-14 教师类
import java.util.Scanner;
class Teacher{
int no;
String name;
String seminary;
int age;
public Teacher(){
}
public Teacher(int no, String name,int age, String seminary) {
this.no = no;
this.name = name;
this.seminary = seminary;
this.age = age;
}
public int getNo() {
return no;
}
public void setNo(int no) {
this.no = no;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSeminary() {
return seminary;
}
public void setSeminary(String seminary) {
this.seminary = seminary;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public boolean equals(Object obj){
Teacher t=(Teacher) obj;
if(this.no==t.no)
return true;
return false;
}
public String toString(){
return "no: "+this.no+", name:"+this.name+", age: "+this.age+", seminary: "+seminary;
}
}
public class Main {
public static void main(String[] args) {
Scanner s=new Scanner(System.in);
Teacher t=new Teacher(s.nextInt(),s.next(),s.nextInt(),s.next());
Teacher t1=new Teacher(s.nextInt(),s.next(),s.nextInt(),s.next());
System.out.println(t.toString());
System.out.println(t1.toString());
System.out.println(t.equals(t1));
}
}
6-1 jmu-Java-06异常-finally
System.out.println("resource open success");
}catch(Exception e){
System.out.println(e);
}
try{
resource.close();
System.out.println("resource release success");
}catch(RuntimeException e){
System.out.println(e);
}
6-2 jmu-Java-06异常-多种类型异常的捕获
catch(NumberFormatException e){
System.out.println("number format exception");
System.out.println(e);
}catch(IllegalArgumentException e){
System.out.println("illegal argument exception");
System.out.println(e);
}catch(Exception e){
System.out.println("other exception");
System.out.println(e);
}
6-3 接口与多态
class Circle implements Shap{
Double r;
final double PI=3.14;
public Circle(double parseDouble) {
super();
this.r = parseDouble;
}
@Override
public double f() {
if(r<=0) return 0;
return 2*PI*r;
}
}
class Rect implements Shap{
Double a,b;
public Rect(double parseDouble, double parseDouble2) {
super();
this.a = parseDouble;
this.b = parseDouble2;
}
@Override
public double f() {
if(a<=0||b<=0) return 0;
return 2*(a+b);
}
}
class Tri implements Shap{
Double a,b,c;
public Tri(double parseDouble, double parseDouble2, double parseDouble3) {
super();
this.a = parseDouble;
this.b = parseDouble2;
this.c = parseDouble3;
}
@Override
public double f() {
if(a+b<c||a+c<b||b+c<a) return 0;
return a+b+c;
}
}
5-1
要求：根据Main类中main方法中的代码，设计满足要求的Student（学生）类：1）包含属性：int no（学号）、String name（姓名）；2）满足Main类中main方法代码的说明要求。 Main类中main方法代码的说明：1）首先，从键盘接收形如“3 cuizhenyu 2 tiangang 1 dingchangqing 4 zhangfeng”的字符串，该字符串中包含了4个学生的学号和姓名（各学生以及学生的学号和姓名之间都用一个空格分隔，姓名中只包含英文字母），然后将该字符串内容中的前3个学生的学号及其姓名放到到Student数组stus中；2）将stus中的3个Student放入到HashSet stuSet中（注意：如果学生的学号相同，则认为是相同对象，不放入stuSet中）；3）将第4个学生对象放入到stuSet中，如果第4个学生对象的学号与stuSet中已有学生对象的学号相同则不能放入。然后，打印出当前stuSet中学生对象的个数；4）用Arrays.sort方法对数组stus按照学生姓名的字母顺序排序（先比较首字母，首字母相同的比较第二个字母，以此类推），输出排序后的stus中3个学生对象的内容，每个学生对象的输出格式为“no=XX&name=YY”。
class Student implements Comparable<Student> {
private int no;
private String name;
public Student(int no, String name) {
this.no = no;
this.name = name;
}
public int getNo() {
return no;
}
public void setNo(int no) {
this.no = no;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String toString() {
return "no=" + no + "&name=" + name;
}
public int compareTo(Student o) {
if(this.name.compareTo(o.name)<0) {
return -1;
}
else if(this.name.compareTo(o.name)>0)return 1;
return 0;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + no;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Student other = (Student) obj;
if (no != other.no)
return false;
return true;
}
}
5-2
class Base {
int x, y, z, w;
public Base(int a, int b) {
x = a;
y = b;
}
public Base(int a, int b, int c, int d) {
空一：this(a,b);
空二：new Base
5-3
根据输出结果，完成填空。
super(x);
System.out.println();
5-4
定义一个Person类，该类包括age，name两个数据成员和eat(),work()两个成员方法，并实现对两个数据成员的Getter方法。然后通过测试程序，实现相应对象的操作。程序输出结果如下
private String name
return name
"会生活"
new Person
p.eat()
5-5
有如下父类和子类的定义，请根据要求填写代码。
super(a);
this.a = a*10;
super.a
this.a
选择：
2-1
以下二维数组的定义正确的是（ ）
B.
int a[][]=new int[3][]
2-2
下面那种类型不属于Java的基本数据类型？
D.
String
下面的数据声明及赋值哪一个是正确的？
D.
int i = 10;
2-4下列标识符（名字）命名原则中，符合规范的是___。
常量完全大写
2-5在JAVA中，给定代码片段如下所示，则编译运行后，输出结果是（）。
for (int i = 0; i < 10; i++) {
if (i == 10 - i) {
break;
}
if (i % 3 != 0) {
continue;
}
System.out.print(i + " ");
}
B.
0 3
2-6
以下选项中没有语法错误的是（ ） 。
C.
int j=0;
for(int k=0; j + k !=10; j++,k++) {
System.out.println(“ j is “+ j + “k is”+ k);
}
2-7
以下代码段将创建几个对象?
String s1="bc";
String s2="bc";
D.
1
2-8
关于垃圾收集的哪些叙述是对的。
B.
垃圾收集将检查并释放不再使用的内存。
2-9
你怎样强制对一个对象立即进行垃圾收集？
E.
垃圾收集是不能被强迫立即执行
2-10
设有定义：String s=”World”;，下列语句错误的是（ ）。
D.
String str=s.append();
2-11
以下代码输出（ ）。
public static void main(String[] args) {
String[] tokens = "Welcome to Java".split("o");
for (int i = 0; i < tokens.length; i++) {
System.out.print(tokens[i] + " ");
}
}
C.
Welc me t Java
2-12
请选择下面程序正确的输出结果（ ）
public class Main{
public static void main(String args[ ]){
String a = new String("A");
String b = new String("B");
mb_operate(a,b);
System.out.println(a + "." + b);
}
static void mb_operate(String x,String y){
x.concat(y);
y=x;
}
}
A.
A.B
2-13
Java中，要对一个类实现for( : )形式的遍历，则该类必须实现下列哪一个接口?
D.
Iterable
2-14
在Java中，( )类可用于创建链表数据结构的对象
A.
LinkedList
2-15
现在有一个方法：public static int info(int x,double y)，下面那个方法是对本方法的正确重载？
C.
public static int info(int x,int y)；
2-16
在Java中，一个类可同时定义许多同名的方法，这些方法的形式参数个数、类型或顺序各不相同，传回的值也可以不相同。这种面向对象程序的特性称为( )。
C.
重载
2-17
假设类A有如下定义，且a是A类的一个实例，则必定错误的选项是（ ）。
class A {
int i;
static String s;
void method1() { }
static void method2() { }
}
C.
A.method1();
2-18
下面关于缺省构造方法的描述中正确的是（ ）
A.
当类中没有定义任何构造方法时，Java编译器将为这个类创建缺省构造方法
2-19
下述哪条关于构造方法的说法，不符合Java语法的规定（ ）。
2-20
以下代码的输出结果为（ ）。
public class Pass{
static int j = 20;
public void amethod(int x){
x = x*2;
j = j*2;
}
public static void main(String args[]){
int i = 10;
Pass p = new Pass();
p.amethod(i);
System.out.println(i+" and "+j);
}
}
C.
10 and 40
2-21一个*.java文件中可以包含多少个public类？
A.
最多1个
2-22
对于构造方法，下列叙述不正确的是（ ）。
B.
构造方法的返回类型只能是void型，即在方法名前加void
2-23
以下程序运行结果是
public class Test {
public int div(int a, int b) {
try {
return a / b;
}catch(Exception e){
System.out.println(“Exception”);
}catch(NullPointerException e){
System.out.println(“ArithmeticException”);
}
catch (ArithmeticException e) {
System.out.println(“ArithmeticException”);
} finally {
System.out.println(“finally”);
}
return 0;
}
public static void main(String[] args) {
Test demo = new Test();
System.out.println(“商是：” + demo.div(9, 0));
}
}
D.
编译报错
2-24
对以下程序进行编译、运行结果是
abstract class MineBase {
abstract void amethod();
static int i;
}
public class Mine extends MineBase{
public static void main(String argv[]){
int[] ar = new int[5];
for(i = 0;i < ar.length;i++)
System.out.println(ar[i]);
}
}
C.
编译出错。
2-25
下列程序的运行结果是（ ）。
public class Test {
public static void main(String[] args) {
try {
System.out.println("Welcome to Java");
int i = 0;
int y = 2 / i;
System.out.println("Welcome to HTML");
}
finally {
System.out.println("The finally clause is executed");
}
}
}
B.
Welcome to Java，下一行是 The finally clause is executed , 然后是错误信息.
2-26
下面哪个标识符不符合Java定义要求？
D.
100Book
2-27
下面（ ）不是Java的关键字。
C.
sizeof
2-28
int型public成员变量MAX_LENGTH，该值保持为常数100，则定义这个变量的语句是（ ）。
D.
public final int MAX_LENGTH = 100
2-29
Java 语言的特点不包括( )
(2分)
C.
多重继承
2-30
编译Java源文件和解释执行Java字节码文件的指令分别是什么？
D.
javac.exe和java.exe
2-31
在Java中，以下（）类的对象是以键-值的方式存储对象。
C.
HashMap
2-32
要想在集合中保存没有重复的元素并且按照一定的顺序排序，可以使用以下（）集合。
D.
TreeSet
2-33
getCustomerInfo()方法如下，try中可以捕获三种类型的异常，如果在该方法运行中产生了一个IOException，将会输出什么结果（ ）。
public void getCustomerInfo() {
try {
// do something that may cause an Exception
} catch (java.io.FileNotFoundException ex){
System.out.print("FileNotFoundException!");
} catch (java.io.IOException ex){
System.out.print("IOException!");
} catch (java.lang.Exception ex){
System.out.print("Exception!");
}
}
A.
IOException!
2-34
下面代码运行结果是
public class Demo{
public int add(int a,int b){
try{
return a+b;
}catch(Exception e){
System.out.println(“catch 语句块”);
}finally{
System.out.println(“finally 语句块”);
}
return 0;
}
public static void main(String[] args){
Demo demo = new Demo();
System.out.println(“和是：”+demo.add(9,34));
}
}
B.
finally语句块 和是：43
2-35
下列程序的错误是（ ）
public class Test {
public static void main (String[] args) {
try {
System.out.println("Welcome to Java");
}
}
}
B.
有一个try块但没有catch块或finally块。
2-36
已知下列代码，如果方法oneMethod()运行异常，则下列哪个语句肯定不会被输出？
public void example(){
try {
oneMethod();
System.out.println("condition1");
}catch(ArrayIndexOutOfBoundsException e) {
System.out.println("condition2");
}catch(Exception e) {
System.out.println("condition3");
}finally{
System.out.println("condition4");
}
A.
condition1
2-37
将以下哪种方法插入行6是不合法的。（ ） 。
1．public class Test1 {
2． public float aMethod（float a，float b） throws
3． IOException { }
4． }
5．public class Test2 extends Test1{
6．
7．}
A.
float aMethod（float a，float b）{ }
2-38
下面的概念，哪个不是关于对象的多态性的体现。
B.
方法的继承
2-39
多态的表现形式有
A.
重写
2-40
class Person {
public void printValue(int i, int j) {//... }
public void printValue(int i){//... }
}
public class Teacher extends Person {
public void printValue() {//... }
public void printValue(int i) {//...}
public static void main(String args[]){
Person t = new Teacher();
t.printValue(10);
}
第10行语句将调用哪行语句？
D.
行7
2-41
如下代码的输出是（ ）。
public class Test {
public static void main(String[] args) {
new Person().printPerson();
new Student().printPerson();
}
}
class Student extends Person {
private String getInfo() {
return "Student";
}
}
class Person {
private String getInfo() {
return "Person";
}
public void printPerson() {
System.out.println(getInfo());
}
}
A.
Person Person
2-42
已知类的继承关系如下：
class Employee;
class Manager extends Employee;
class Director extends Employee; 则以下语句哪个能通过编译？ ( )。
A.
Employee e = new Manager();
2-43
设类B是类C的父类，下列声明对象x1的语句中不正确的是?
D.
C x1=new B( );
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