Java面试题及答案（代码题19道）

JAVA代码查错
1.
abstract class Name {
   private String name;
   public abstract boolean isStupidName(String name) {}
}
大侠们，这有何错误?
答案: 错。abstract method必须以分号结尾，且不带花括号。
2.
public class Something {
   void doSomething () {
       private String s = "";
       int l = s.length();
   }
}
有错吗?
答案: 错。局部变量前不能放置任何访问修饰符 (private，public，和protected)。final可以用来修饰局部变量
(final如同abstract和strictfp，都是非访问修饰符，strictfp只能修饰class和method而非variable)。
3.
abstract class Something {
   private abstract String doSomething ();
}
这好像没什么错吧?
答案: 错。abstract的methods不能以private修饰。abstract的methods就是让子类implement(实现)具体细节的，怎么可以用private把abstract
method封锁起来呢? (同理，abstract method前不能加final)。
4.
public class Something {
   public int addOne(final int x) {
       return ++x;
   }
}
这个比较明显。
答案: 错。int x被修饰成final，意味着x不能在addOne method中被修改。
5.
public class Something {
   public static void main(String[] args) {
       Other o = new Other();
       new Something().addOne(o);
   }
   public void addOne(final Other o) {
       o.i++;
   }
}
class Other {
   public int i;
}
和上面的很相似，都是关于final的问题，这有错吗?
答案: 正确。在addOne method中，参数o被修饰成final。如果在addOne method里我们修改了o的reference
(比如: o = new Other();)，那么如同上例这题也是错的。但这里修改的是o的member vairable
(成员变量)，而o的reference并没有改变。
6.
class Something {
    int i;
    public void doSomething() {
        System.out.println("i = " + i);
    }
}
有什么错呢? 看不出来啊。
答案: 正确。输出的是"i = 0"。int i属於instant variable (实例变量，或叫成员变量)。instant variable有default value。int的default value是0。
7.
class Something {
    final int i;
    public void doSomething() {
        System.out.println("i = " + i);
    }
}
和上面一题只有一个地方不同，就是多了一个final。这难道就错了吗?
答案: 错。final int i是个final的instant variable (实例变量，或叫成员变量)。final的instant variable没有default value，必须在constructor (构造器)结束之前被赋予一个明确的值。可以修改为"final int i = 0;"。
8.
public class Something {
     public static void main(String[] args) {
        Something s = new Something();
        System.out.println("s.doSomething() returns " + doSomething());
    }
    public String doSomething() {
        return "Do something ...";
    }
}
看上去很完美。
答案: 错。看上去在main里call doSomething没有什么问题，毕竟两个methods都在同一个class里。但仔细看，main是static的。static method不能直接call non-static methods。可改成"System.out.println("s.doSomething() returns " + s.doSomething());"。同理，static method不能访问non-static instant variable。
9.
此处，Something类的文件名叫OtherThing.java
class Something {
    private static void main(String[] something_to_do) {      
        System.out.println("Do something ...");
    }
}
这个好像很明显。
答案: 正确。从来没有人说过Java的Class名字必须和其文件名相同。但public class的名字必须和文件名相同。
10．
interface  A{
   int x = 0;
}
class B{
   int x =1;
}
class C extends B implements A {
   public void pX(){
      System.out.println(x);
   }
   public static void main(String[] args) {
      new C().pX();
   }
}
答案：错误。在编译时会发生错误(错误描述不同的JVM有不同的信息，意思就是未明确的x调用，两个x都匹配（就象在同时import java.util和java.sql两个包时直接声明Date一样）。对于父类的变量,可以用super.x来明确，而接口的属性默认隐含为 public static final.所以可以通过A.x来明确。
11.
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。
答案: 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。
JAVA编程题
1．现在输入n个数字，以逗号，分开；然后可选择升或者降序排序；按提交键就在另一页面显示按什么排序，结果为，提供reset
import java.util.*;
public class bycomma{
public static String[] splitStringByComma(String source){
   if(source==null||source.trim().equals(""))
    return null;
   StringTokenizer commaToker = new StringTokenizer(source,",");
   String[] result = new String[commaToker.countTokens()];
   int i=0;
   while(commaToker.hasMoreTokens()){
    result[i] = commaToker.nextToken();
    i++;
   }
   return result;
}
public static void main(String args[]){
String[] s = splitStringByComma("5,8,7,4,3,9,1");
int[] ii = new int[s.length];
for(int i = 0;i<s.length;i++){
ii[i] =Integer.parseInt(s[i]);
}
    Arrays.sort(ii);
    //asc
    for(int i=0;i<s.length;i++){
    System.out.println(ii[i]);
    }
    //desc
    for(int i=(s.length-1);i>=0;i--){
    System.out.println(ii[i]);
    }
}
}
2．金额转换，阿拉伯数字的金额转换成中国传统的形式如：（￥1011）－>（一千零一拾一元整）输出。
package test.format;
import java.text.NumberFormat;
import java.util.HashMap;
public class SimpleMoneyFormat {
  public static final String EMPTY = "";
  public static final String ZERO = "零";
  public static final String ONE = "壹";
  public static final String TWO = "贰";
  public static final String THREE = "叁";
  public static final String FOUR = "肆";
  public static final String FIVE = "伍";
  public static final String SIX = "陆";
  public static final String SEVEN = "柒";
  public static final String EIGHT = "捌";
  public static final String NINE = "玖";
  public static final String TEN = "拾";
  public static final String HUNDRED = "佰";
  public static final String THOUSAND = "仟";
  public static final String TEN_THOUSAND = "万";
  public static final String HUNDRED_MILLION = "亿";
  public static final String YUAN = "元";
  public static final String JIAO = "角";
  public static final String FEN = "分";
  public static final String DOT = ".";

  private static SimpleMoneyFormat formatter = null;
  private HashMap chineseNumberMap = new HashMap();
  private HashMap chineseMoneyPattern = new HashMap();
  private NumberFormat numberFormat = NumberFormat.getInstance();

  private SimpleMoneyFormat() {
    numberFormat.setMaximumFractionDigits(4);
    numberFormat.setMinimumFractionDigits(2);
    numberFormat.setGroupingUsed(false);

    chineseNumberMap.put("0", ZERO);
    chineseNumberMap.put("1", ONE);
    chineseNumberMap.put("2", TWO);
    chineseNumberMap.put("3", THREE);
    chineseNumberMap.put("4", FOUR);
    chineseNumberMap.put("5", FIVE);
    chineseNumberMap.put("6", SIX);
    chineseNumberMap.put("7", SEVEN);
    chineseNumberMap.put("8", EIGHT);
    chineseNumberMap.put("9", NINE);
    chineseNumberMap.put(DOT, DOT);

    chineseMoneyPattern.put("1", TEN);
    chineseMoneyPattern.put("2", HUNDRED);
    chineseMoneyPattern.put("3", THOUSAND);
    chineseMoneyPattern.put("4", TEN_THOUSAND);
    chineseMoneyPattern.put("5", TEN);
    chineseMoneyPattern.put("6", HUNDRED);
    chineseMoneyPattern.put("7", THOUSAND);
    chineseMoneyPattern.put("8", HUNDRED_MILLION);
  }

  public static SimpleMoneyFormat getInstance() {
    if (formatter == null)
      formatter = new SimpleMoneyFormat();
    return formatter;
  }

  public String format(String moneyStr) {
    checkPrecision(moneyStr);
    String result;
    result = convertToChineseNumber(moneyStr);
    result = addUnitsToChineseMoneyString(result);
    return result;
  }

  public String format(double moneyDouble) {
    return format(numberFormat.format(moneyDouble));
  }

  public String format(int moneyInt) {
    return format(numberFormat.format(moneyInt));
  }

  public String format(long moneyLong) {
    return format(numberFormat.format(moneyLong));
  }

  public String format(Number moneyNum) {
    return format(numberFormat.format(moneyNum));
  }

  private String convertToChineseNumber(String moneyStr) {
    String result;
    StringBuffer cMoneyStringBuffer = new StringBuffer();
    for (int i = 0; i < moneyStr.length(); i++) {
      cMoneyStringBuffer.append(chineseNumberMap.get(moneyStr.substring(i, i + 1)));
    }
    //拾佰仟万亿等都是汉字里面才有的单位，加上它们
    int indexOfDot = cMoneyStringBuffer.indexOf(DOT);
    int moneyPatternCursor = 1;
    for (int i = indexOfDot - 1; i > 0; i--) {
      cMoneyStringBuffer.insert(i, chineseMoneyPattern.get(EMPTY + moneyPatternCursor));
      moneyPatternCursor = moneyPatternCursor == 8 ? 1 : moneyPatternCursor + 1;
    }

    String fractionPart = cMoneyStringBuffer.substring(cMoneyStringBuffer.indexOf("."));
    cMoneyStringBuffer.delete(cMoneyStringBuffer.indexOf("."), cMoneyStringBuffer.length());
    while (cMoneyStringBuffer.indexOf("零拾") != -1) {
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零拾"), cMoneyStringBuffer.indexOf("零拾") + 2, ZERO);
    }
    while (cMoneyStringBuffer.indexOf("零佰") != -1) {
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零佰"), cMoneyStringBuffer.indexOf("零佰") + 2, ZERO);
    }
    while (cMoneyStringBuffer.indexOf("零仟") != -1) {
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零仟"), cMoneyStringBuffer.indexOf("零仟") + 2, ZERO);
    }
    while (cMoneyStringBuffer.indexOf("零万") != -1) {
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零万"), cMoneyStringBuffer.indexOf("零万") + 2, TEN_THOUSAND);
    }
    while (cMoneyStringBuffer.indexOf("零亿") != -1) {
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零亿"), cMoneyStringBuffer.indexOf("零亿") + 2, HUNDRED_MILLION);
    }
    while (cMoneyStringBuffer.indexOf("零零") != -1) {
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零零"), cMoneyStringBuffer.indexOf("零零") + 2, ZERO);
    }
    if (cMoneyStringBuffer.lastIndexOf(ZERO) == cMoneyStringBuffer.length() - 1)
      cMoneyStringBuffer.delete(cMoneyStringBuffer.length() - 1, cMoneyStringBuffer.length());
    cMoneyStringBuffer.append(fractionPart);

    result = cMoneyStringBuffer.toString();
    return result;
  }


  private String addUnitsToChineseMoneyString(String moneyStr) {
    String result;
    StringBuffer cMoneyStringBuffer = new StringBuffer(moneyStr);
    int indexOfDot = cMoneyStringBuffer.indexOf(DOT);
    cMoneyStringBuffer.replace(indexOfDot, indexOfDot + 1, YUAN);
    cMoneyStringBuffer.insert(cMoneyStringBuffer.length() - 1, JIAO);
    cMoneyStringBuffer.insert(cMoneyStringBuffer.length(), FEN);
    if (cMoneyStringBuffer.indexOf("零角零分") != -1)//没有零头，加整
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零角零分"), cMoneyStringBuffer.length(), "整");
    else
    if (cMoneyStringBuffer.indexOf("零分") != -1)//没有零分，加整
      cMoneyStringBuffer.replace(cMoneyStringBuffer.indexOf("零分"), cMoneyStringBuffer.length(), "整");
    else {
      if(cMoneyStringBuffer.indexOf("零角")!=-1)
        cMoneyStringBuffer.delete(cMoneyStringBuffer.indexOf("零角"),cMoneyStringBuffer.indexOf("零角")+2);
//      tmpBuffer.append("整");
    }
    result = cMoneyStringBuffer.toString();
    return result;
  }

  private void checkPrecision(String moneyStr) {
    int fractionDigits = moneyStr.length() - moneyStr.indexOf(DOT) - 1;
    if (fractionDigits > 2)
      throw new RuntimeException("金额" + moneyStr + "的小数位多于两位。"); //精度不能比分低
  }

  public static void main(String args[]) {
    System.out.println(getInstance().format(new Double(10010001.01)));
  }
}
3、继承时候类的执行顺序问题,一般都是选择题,问你将会打印出什么?
答:父类：
package test;
public class FatherClass {
public FatherClass() {
System.out.println("FatherClass Create");
}
}
子类:
package test;
import test.FatherClass;
public class ChildClass extends FatherClass {
public ChildClass() {
System.out.println("ChildClass Create");
}
public static void main(String[] args) {
FatherClass fc = new FatherClass();
ChildClass cc = new ChildClass();
}
}
输出结果：
C:>java test.ChildClass
FatherClass Create
FatherClass Create
ChildClass Create
4、内部类的实现方式?
答：示例代码如下：
package test;
public class OuterClass {
private class InterClass {
public InterClass() {
System.out.println("InterClass Create");
}
}
public OuterClass() {
InterClass ic = new InterClass();
System.out.println("OuterClass Create");
}
public static void main(String[] args) {
OuterClass oc = new OuterClass();
}
}
输出结果:
C:>java test/OuterClass
InterClass Create
OuterClass Create
再一个例题：
public class OuterClass {
private double d1 = 1.0;
//insert code here
}
You need to insert an inner class declaration at line 3. Which two inner class declarations are
valid?(Choose two.)
A. class InnerOne{
public static double methoda() {return d1;}
}
B. public class InnerOne{
static double methoda() {return d1;}
}
C. private class InnerOne{
double methoda() {return d1;}
}
D. static class InnerOne{
protected double methoda() {return d1;}
}
E. abstract class InnerOne{
public abstract double methoda();
}
说明如下：
一.静态内部类可以有静态成员，而非静态内部类则不能有静态成员。 故 A、B 错
二.静态内部类的非静态成员可以访问外部类的静态变量，而不可访问外部类的非静态变量；return d1 出错。故 D 错
三.非静态内部类的非静态成员可以访问外部类的非静态变量。 故 C 正确
四.答案为C、E
5、Java 的通信编程，编程题(或问答)，用JAVA SOCKET编程，读服务器几个字符，再写入本地显示？
答:Server端程序:
package test;
import java.net.*;
import java.io.*;
public class Server {
private ServerSocket ss;
private Socket socket;
private BufferedReader in;
private PrintWriter out;
public Server() {
try {
ss=new ServerSocket(10000);
while(true) {
socket = ss.accept();
String RemoteIP = socket.getInetAddress().getHostAddress();
String RemotePort = ":"+socket.getLocalPort();
System.out.println("A client come in!IP:"+RemoteIP+RemotePort);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String line = in.readLine();
System.out.println("Cleint send is :" + line);
out = new PrintWriter(socket.getOutputStream(),true);
out.println("Your Message Received!");
out.close();
in.close();
socket.close();
}
}
catch (IOException e) {
out.println("wrong");
}
}
public static void main(String[] args) {
new Server();
}
}
Client端程序:
package test;
import java.io.*;
import java.net.*;
public class Client {
Socket socket;
BufferedReader in;
PrintWriter out;
public Client() {
try {
System.out.println("Try to Connect to 127.0.0.1:10000");
socket = new Socket("127.0.0.1",10000);
System.out.println("The Server Connected!");
System.out.println("Please enter some Character:");
BufferedReader line = new BufferedReader(new InputStreamReader(System.in));
out = new PrintWriter(socket.getOutputStream(),true);
out.println(line.readLine());
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
System.out.println(in.readLine());
out.close();
in.close();
socket.close();
}
catch(IOException e) {
out.println("Wrong");
}
}
public static void main(String[] args) {
new Client();
}
}

6、用JAVA实现一种排序，JAVA类实现序列化的方法(二种)？ 如在COLLECTION框架中，实现必须要实现什么样的接口？
答:用插入法进行排序代码如下
package test;
import java.util.*;
class InsertSort {
ArrayList al;
public InsertSort(int num,int mod) {
al = new ArrayList(num);
Random rand = new Random();
System.out.println("The ArrayList Sort Before:");
for (int i=0;i<num ;i++ ) {
al.add(new Integer(Math.abs(rand.nextInt()) % mod + 1));
System.out.println("al["+i+"]="+al.get(i));
}
}
public void SortIt() {
Integer tempInt;
int MaxSize=1;
for(int i=1;i<al.size();i++) {
tempInt = (Integer)al.remove(i);
if(tempInt.intValue()>=((Integer)al.get(MaxSize-1)).intValue()) {
al.add(MaxSize,tempInt);
MaxSize++;
System.out.println(al.toString());
}
else {
for (int j=0;j<MaxSize ;j++ ) {
if (((Integer)al.get(j)).intValue()>=tempInt.intValue()) {
al.add(j,tempInt);
MaxSize++;
System.out.println(al.toString());
break;
}
}
}
}
System.out.println("The ArrayList Sort After:");
for(int i=0;i<al.size();i++) {
System.out.println("al["+i+"]="+al.get(i));
}
}
public static void main(String[] args) {
InsertSort is = new InsertSort(10,100);
is.SortIt();
}
}
JAVA类实现序例化的方法是实现java.io.Serializable接口
Collection框架中实现必须要实现Comparable 接口和 Comparator 接口
7、编程：编写一个截取字符串的函数，输入为一个字符串和字节数，输出为按字节截取的字符串。 但是要保证汉字不被截半个，如“我ABC”4，应该截为“我AB”，输入“我ABC汉DEF”，6，应该输出为“我ABC”而不是“我ABC+汉的半个”。
答：代码如下：
package test;
class SplitString {
String SplitStr;
int SplitByte;
public SplitString(String str,int bytes) {
SplitStr=str;
SplitByte=bytes;
System.out.println("The String is:′"+SplitStr+"′;SplitBytes="+SplitByte);
}
public void SplitIt() {
int loopCount;
loopCount=(SplitStr.length()%SplitByte==0)?(SplitStr.length()/SplitByte):(SplitStr.length()/SplitByte+1);
System.out.println("Will Split into "+loopCount);
for (int i=1;i<=loopCount ;i++ ) {
if (i==loopCount){
System.out.println(SplitStr.substring((i-1)*SplitByte,SplitStr.length()));
}
else {
System.out.println(SplitStr.substring((i-1)*SplitByte,(i*SplitByte)));
}
}
}
public static void main(String[] args) {
SplitString ss = new SplitString("test中dd文dsaf中男大3443n中国43中国人
0ewldfls=103",4);
ss.SplitIt();
}
}
8. 请不运行程序先写出你认为的输出结果：
public class Test2 extends Test1{
{
    System.out.print("1");
}
Test2(){
    System.out.print("2");
}
static{
System.out.print("3");
}
{
System.out.print("4");
}
public static void main(String[] args) {
new Test2();
}
}
class Test1 {
Test1(){
System.out.print("5");
}
static{
System.out.print("6");
}
}