Java面试笔试题大汇总

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?。
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;iii[i] =Integer.parseInt(s[i]);

}

Arrays.sort(ii);

//asc

for(int i=0;iSystem.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);