经典JAVA算法题册

Java的16进制与字符串的相互转换函数

/**
 * 将指定 byte 数组以 16 进制的形式打印到控制台
 * @param hint String
 * @param b byte[]
 * @return void
*/
public static void printHexString(String hint, byte[] b) {
 System.out.print(hint);
 for (int i = 0; i < b.length; i++) {
 String hex = Integer.toHexString(b[i] & 0xFF);
 if (hex.length() == 1) {
 hex = '0' + hex;
 }
 System.out.print(hex.toUpperCase() + " ");
 }
 System.out.println("");
}
/**
*
* @param b byte[]
* @return String
*/
public static String Bytes2HexString(byte[] b) {
 String ret = "";
 for (int i = 0; i < b.length; i++) {
 String hex = Integer.toHexString(b[i] & 0xFF);
 if (hex.length() == 1) {
 hex = '0' + hex;
 }
 ret += hex.toUpperCase();
 }
 return ret;
}
/**
* 将两个 ASCII 字符合成一个字节；
* 如："EF"--> 0xEF
* @param src0 byte
* @param src1 byte
* @return byte
*/
public static byte uniteBytes(byte src0, byte src1) {
 byte _b0 = byte.decode("0x" + new String(new byte[]{src0})).byteValue();
 _b0 = (byte)(_b0 << 4);
 byte _b1 = byte.decode("0x" + new String(new byte[]{src1})).byteValue();
 byte ret = (byte)(_b0 ^ _b1);
 return ret;
}
/**
* 将指定字符串 src，以每两个字符分割转换为 16 进制形式
* 如："2B44EFD9" --> byte[]{0x2B, 0x44, 0xEF, 0xD9}
* @param src String
* @return byte[]
 */
public static byte[] HexString2Bytes(String src){
 byte[] ret = new byte[8];
 byte[] tmp = src.getBytes();
 for (int i=0; i<8; i++){
 ret[i] = uniteBytes(tmp[i*2], tmp[i*2+1]);
 }
 return ret;
}

JAVA时间格式化处理

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将毫秒转化为日期

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public static void main(String[] args) {
 new ConvertLong2Date().launchFrame();
}
public String convertL2D(long l) {
 long _l = 0L;
 Date _d = null;
 SimpleDateFormat _sdf = null;
 String _s = null;
 _l = l;
 _d = new Date(_l);
 _sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
 _s = _sdf.format(_d);
 return _s;
}

文本的倒序输出

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文件 before:

Hello
World

要求输出文件 after:

World
Hello

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.ListIterator;
public class ReverseOrder extends ArrayList {
 public static String read(String fileName) throws IOException {
 StringBuffer sb = new StringBuffer();
 LinkedList lines = new LinkedList();
 BufferedReader in = new BufferedReader(new FileReader(fileName));
 String s;
 while ((s = in.readLine()) != null)
 lines.add(s);
 in.close();
 ListIterator it = lines.listIterator(lines.size());
 while (it.hasPrevious()) {
 sb.append(it.previous());
 sb.append("n");
}
return sb.toString();
}
public static void write(String fileName, String text) throws IOException { PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(
fileName)));
out.print(text);
out.close();
}
public ReverseOrder(String fileName) throws IOException { super(Arrays.asList(read(fileName).split("n")));
}
public void write(String fileName) throws IOException {
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter( fileName)));
for (int i = 0; i < size(); i++)
out.println(get(i));
out.close();
}
public static void main(String[] args) throws Exception { String fileName = "e:\1124\before.txt";
ReverseOrder text = new ReverseOrder(fileName);
text.write("e:\1124\after.txt");
}
/*
* 最后会多一个空行，手工删除一下
*/
}

判断一个数字是奇数还是偶数

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判断一个数是否是奇数：

public static Boolean isOdd(int i) {
 return (i&1) != 0;
}

判断一个数是否是偶数

public static Boolean isEven(int i) {
 return (i&1) = 0;
}
//位运算符说明在 java 文件夹里面

用Hibernate实现分页

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public List queryByStatus(int status, int currentPage, int lineSize)
throws Exception {
 List all = null;
 String hql = "FROM Question AS q WHERE q.status=? ORDER BY q.questiontime desc";
 Query q = super.getSession().createQuery(hql);
 q.setInteger(0, status);
 q.setFirstResult((currentPage - 1) * lineSize);
 q.setMaxResults(lineSize);
 all = q.list();
 return all;
}

35选7彩票程序

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public class caipiao
{
 static void generate()
 {
 int a[]=new int[7];
 int i,m,j;
 fan:for (j=0;j <7;j++){
 //外循环实现随机生成每组 7 个数
 a[j]=(int)(Math.random()*35+1);
 m=a[j];
 if(j>=1){
 for (i=0;i <j;i++)//内循环实现无重复
 if(a[i]==m){
 j--;
 continue fan;
 }
 }
 if(a[j] <10)
 System.out.print("0"+a[j]+" "); else
 System.out.print(a[j]+" ");
 }
 }

 public static void main (String args[]){
    int n=Integer.parseint(args[0]);
    System.out.println("中国福利彩票 35 选 7");
    for (int i=0;i <n;i++){
    //循环调用方法实现输出 n 组数
    generate();
    System.out.println();
 }
 }
}

获取GMT8时间

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/**
* Description: 获取 GMT8 时间
* @return 将当前时间转换为 GMT8 时区后的 Date */
public static Date getGMT8Time(){
 Date gmt8 = null;
 try {
 Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("GMT+8"),Locale.CHINESE);
 Calendar day = Calendar.getInstance();
 day.set(Calendar.YEAR, cal.get(Calendar.YEAR));
 day.set(Calendar.MONTH, cal.get(Calendar.MONTH));
 day.set(Calendar.DATE, cal.get(Calendar.DATE));
 day.set(Calendar.HOUR_OF_DAY, cal.get(Calendar.HOUR_OF_DAY));
 day.set(Calendar.MINUTE, cal.get(Calendar.MINUTE));
 day.set(Calendar.SECOND, cal.get(Calendar.SECOND));
 gmt8 = day.getTime();
 }
 catch (Exception e) {
 System.out.println("获取 GMT8 时间 getGMT8Time() error !");
 e.printStackTrace();
 gmt8 = null;
 }
 return gmt8;
}

中文乱码转换

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public String china(String args)
{
 String s=null;
 String s=new String(args.getBytes("ISO-8859-1"),"gb2312");
 return s;
}

小标签

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import java.io.IOException;
import java.util.List;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import com.formcontent.show.ShowFormTypeOperateDb;
import com.forum.hibernatePrj.Space;
public class OutPrintForumType extends TagSupport{
 public int doStartTag() throws JspException
 {
 String printStr="";
 ShowFormTypeOperateDb showtype=new ShowFormTypeOperateDb();
 List list=showtype.getForumType();
 if(list!=null&&list.size()>0)
 {
 for (int i=0;i <list.size();i++)
 {
 Space space=(Space)list.get(i);
 if(space!=null)
 {
 printStr+=" <tr> <td>"+" <div align='left' class='TypeCss'>"+
 space.getSpaceName()+" "+space.getSpaceDescription()+" <br/>目前登陆总人数:"+i+" 人访问数:"+i+"人 </div> </td> </tr>"
 +" <tr> <td> </td> </tr>";
 }
 }
 }
 try {
 pageContext.getOut().write(printStr);
 }
 catch (IOException e) {
 e.printStackTrace();
 }
 return super.doStartTag();
 }
}

Big5字与Unicode的互换

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/**
* Big5 字与 Unicode 的互换
* 转换后的正常字型
*/
import java.io.*;
public class MyUtil{
 public static String big5ToUnicode(String s){
 try{
 return new String(s.getBytes("ISO8859_1"), "Big5");
 }
 catch (UnsupportedEncodingException uee){
 return s;
 }
 }
 public static String UnicodeTobig5(String s){
 try{
 return new String(s.getBytes("Big5"), "ISO8859_1");
 }
 catch (UnsupportedEncodingException uee){
 return s;
 }
 }
 public static String toHexString(String s){
 String str="";
 for (int i=0; i<s.length(); i++){
 int ch=(int)s.charAt(i);
 String s4="0000"+Integer.toHexString(ch);
 str=str+s4.substring(s4.length()-4)+" ";
 }
 return str;
 }
}

取得服务器当前的各种具体时间

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/**
* 取得服务器当前的各种具体时间
* 回车：日期时间
*/
import java.util.*;
public class GetNowDate{
 Calendar calendar = null;
 public GetNowDate(){
 calendar = Calendar.getInstance();
 calendar.setTime(new Date());
 }
 public int getYear(){
 return calendar.get(Calendar.YEAR);
 }
 public int getMonth(){
 return 1 + calendar.get(Calendar.MONTH);
 }
 public int getDay(){
 return calendar.get(Calendar.DAY_OF_MONTH);
 }
 public int getHour(){
 return calendar.get(Calendar.HOUR_OF_DAY);
 }
 public int getMinute(){
 return calendar.get(Calendar.MINUTE);
 }
 public int getSecond(){
 return calendar.get(Calendar.SECOND);
 }
 public String getDate(){
 return getMonth()+"/"+getDay()+"/"+getYear();
 }
 public String getTime(){
 return getHour()+":"+getMinute()+":"+getSecond();
 }
 public String getDate2(){
 String yyyy="0000", mm="00", dd="00";
 cy = yyyy + getYear();
 mm = mm + getMonth();
 dd = dd + getDay();
 cy = yyyy.substring(yyyy.length()-4);
 mm = mm.substring(mm.length()-2);
 dd = dd.substring(dd.length()-2);
 return yyyy + "/" + mm + "/" + dd;
 }
 public String getTime2(){
 String hh="00", mm="00", ss="00";
 ah = hh + getHour();
 mm = mm + getMinute();
 ss = ss + getSecond();
 hh = hh.substring(hh.length()-2, hh.length());
 mm = mm.substring(mm.length()-2, mm.length());
 ss = ss.substring(ss.length()-2, ss.length());
 return hh + ":" + mm + ":" + ss;
 }
}

用半角的特殊符号代替全角的特殊符号

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/**
* 用半角的特殊符号代替全角的特殊符号
* 防止特殊字符在传输参数时出现错误
*/
public class ReplaceStrE{
 public static String rightToError(String ss){
 String strs;
 String strs1;
 String strs2;
 String strs3;
 String strs4;
 try{
 strs = ss.replace('＃','#');
 }
 catch(Exception ex){
 return ss;
 }
 try{
 strs1 = strs.replace('＂','"');
 }
 catch(Exception ex){
 return strs;
 }
 try{
 strs2 = strs1.replace(' ','&');
 }
 catch(Exception ex){
 return strs1;
 }
 try{
 strs3 = strs2.replace('＋','+');
 }
 catch(Exception ex){
 return strs2;
 }
 try{
 strs4 = strs3.replace('＇',''');
}
catch(Exception ex){
return ss;
}
return strs4;
}
}

数组和数组之间的转换代码

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import java.lang.reflect.Array;
import java.util.Date;
public class TestCast {
 /** 
* 将数组 array 转换成 clss 代表的类型后返回
* @param array 需要转换的数组
* @param clss 要转换成的类型
* @return 转换后的数组
*/
 public static Object cast(Object array,Class clss){
 if(null==clss)
 throw new IllegalArgumentException("argument clss cannot be null");
 if(null==array)
 throw new IllegalArgumentException("argument array cannot be null");
 if(false==array.getClass().isArray())
 throw new IllegalArgumentException("argument array must be array");
 Object[] src=(Object[])array;
 Object[] dest=(Object[])Array.newInstance(clss, src.length);
 System.arraycopy(src, 0, dest, 0, src.length);
 return dest;
 }
}

从资源文件里读取值的类

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从资源文件里读取值的类，文件后缀不一定要.Properties，只要里面内容如：url=www.cnsec.net可通过 key（url）取得值-www.cnsec.net，简单、强大

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Properties;
/**
* ReadProperties.java
* Description: 读取操作属性配置文件
* @author li.b
* @version 2.0
* Jun 26, 2008
*/
public class ReadProperties {
 /**
* Description: 获取属性配置文件
* @param path 资源文件路径
* @return Properties Object
* @throws FileNotFoundException
* @throws IOException
*/
 public static Properties getProperties(String path) throws FileNotFoundException, IOException{
 Properties props = null;
 File file = new File(path);
 if(file.exists() && file.isFile()){
 props = new Properties();
 props.load(new FileInputStream(file));
 } else{
 System.out.println(file.toString() + "不存在！");
 }
 return props;
 }
 /**
* Description: 从属性文件获取值
* @param props Properties Object
* @param key
* @return 通过 key 匹配到的 value
*/
 public static String getValue(Properties props,String key,String encod){
 String result = "";
 String en = "";
 String localEN = System.getProperty("file.encoding");
 if(encod !=null && !encod.equals("") ){
 en = encod;
 } else{
 en = localEN;
 }
 try {
 key = new String(key.getBytes(en),"ISO-8859-1");
 result = props.getProperty(key);
 if(!result.equals("")){
 result = new String(result.getBytes("ISO-8859-1"),en);
 }
 }
 catch (Exception e) {
 }
 finally{
 if(result == null)result = "";
 return result;
 }
 }
 public static String getValue(Properties props,String key){
 return getValue(props, key, "");
 }
}

一个随机类

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/*
* @author www.wuliaokankan.cn
* Copyright (C) 2007 
* All rights reserved.
*/
package com.dextrys.trilogy.util;
import java.util.Arrays;
import org.eclipse.swt.graphics.RGB;
public class RandomUtil
{
 /**
* @param args */
 public static void main( String[] args )
 {
 //System.out.println( getRandomNormalString( 8 ) );
 int[] test = getRandomIntWithoutReduplicate( 0, 40, 39 );
 Arrays.sort( test );
 for ( int i : test )
 {
 System.out.println( i );
 }
 }
 /**
* get a integer array filled with random integer without reduplicate [min, max)
* @param min the minimum value
 * @param max the maximum value
 * @param size the capacity of the array
 * @return a integer array filled with random integer without redupulicate */
 public static int[] getRandomIntWithoutReduplicate( int min, int max, int size )
 {
 int[] result = new int[size];
 int arraySize = max - min;
 int[] intArray = new int[arraySize];
 // init intArray
 for ( int i = 0 ; i < intArray.length ; i++ )
 {
 intArray[i] = i + min;
 }
 / get randome interger without reduplicate for ( int i = 0 ; i < size ; i++ )
 {
 int c = getRandomint( min, max - i );
 int index = c - min;
 swap( intArray, index, arraySize - 1 - i );
 result[i] = intArray[ arraySize - 1 - i ];
 }
 return result;
 }
 private static void swap( int[] array, int x, int y )
 {
 int temp = array[x];
 array[x] = array[y];
 array[y] = temp;
 }
 /**
* get a random Integer with the range [min, max)
* @param min the minimum value
* @param max the maximum value
* @return the random Integer value
*/
 public static int getRandomint( int min, int max )
 {
 // include min, exclude max
 int result = min + new double( Math.random() * ( max - min ) ).intValue();
 return result;
 }
 /**
* get a random double with the range [min, max)
* @param min the minimum value
* @param max the maximum value
* @return the random double value
*/
 public static double getRandomdouble( double min, double max )
 {
 // include min, exclude max
 double result = min + ( Math.random() * ( max - min ) );
 return result;
 }
 /**
*
* @return a random char with the range ASCII 33(!) to ASCII 126(~) */
 public static char getRandomchar()
 {
 / from ASCII code 33 to ASCII code 126 int firstchar = 33;
 // "!"
 int lastchar = 126;
 // "~"
 char result = ( char ) ( getRandomint( firstchar, lastchar + 1 ) );
 return result;
 }
 /**
*
* @return a random rgb color */
 public static RGB getRandomRGB()
 {
 int red = getRandomint(0,256);
 int green = getRandomint(0,256);
 int blue = getRandomint(0,256);
 return new RGB( red, green, blue );
 }
 /**
*
* @return a random char with the range [0-9],[a-z],[A-Z] */
 public static char getRandomNormalchar()
 {
 // include 0-9,a-z,A-Z
 int number = getRandomint( 0, 62 );
 int zerochar = 48;
 int ninechar = 57;
 int achar = 97;
 int zchar = 122;
 int Achar = 65;
 int Zchar = 90;
 char result;
 if( number < 10 )
 {
 result = ( char ) ( getRandomint( zerochar, ninechar + 1 ) );
 return result;
 } else if( number >= 10 && number < 36 )
 {
 result = ( char ) ( getRandomint( Achar, Zchar + 1 ) );
 return result;
 } else if( number >= 36 && number < 62 )
 {
 result = ( char ) ( getRandomint( achar, zchar + 1 ) );
 return result;
 } else
 {
 return 0;
 }
 }
 /**
*
* @param length the length of the String
* @return a String filled with random char */
 public static String getRandomString( int length )
 {
 / include ASCII code from 33 to 126 StringBuffer result = new StringBuffer();
 for ( int i = 0; i < length; i++ )
 {
 result.append( getRandomchar() );
 }
 return result.toString();
 }
 /**
*
* @param length the length of the String
* @return a String filled with normal random char */
 public static String getRandomNormalString( int length )
 {
 // include 0-9,a-z,A-Z
 StringBuffer result = new StringBuffer();
 for ( int i = 0; i < length; i++)
 {
 result.append( getRandomNormalchar() );
 }
 return result.toString();
 }
}

计算传入值是否星期六

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/**
* 计算传入值是否星期六
* 回车：true or false
*/
import java.util.*;
public class Week6 {
 public Boolean checkWeek6(String str){
 Boolean flag=false;
 int week6=0;
 str.replace('/','-');
 Calendar cal=Calendar.getInstance();
 cal.setTime(java.sql.Date.valueOf(str.substring(0,10)));
 week6=cal.get(Calendar.DAY_OF_WEEK);
 if(week6==7){
 flag=true;
 }
 return flag;
 }
}

转换文件大小

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import java.text.DecimalFormat;
import java.util.Hashtable;
/**
* 文件大小单位转换
* @author Administrator
*/
public class UnitsConversion extends DecimalFormat {
 private static final long serialVersionUID = 3168068393840262910L;
 /**
* 存放有效单位的数组
*/
 private static Hashtable<String, String> validUnits = new Hashtable<String, String>();
 /**
* 限制文件大小上限为 1G
*/
 private static int GB_MAX_SIZE = 1;
 /**
* 最大的 MB 值
*/
 private static int MB_MAX_SIZE = GB_MAX_SIZE * 1024;
 /**
* 最大的 KB 值
*/
 private static int KB_MAX_SIZE = MB_MAX_SIZE * 1024;
 /**
* 最大的 Bytes 值
*/
 private static int BYTES_MAX_SIZE = KB_MAX_SIZE * 1024;
 /**
* 数字部分的值
*/
 private double numPart;
 /**
* 原始的单位字符串
*/
 private String originalUnit;
 /**
* 标准的单位字符串
*/
 private String unit;
 /**
* 转换后的结果
*/
 private String result;
 / 添加所有有效单位 static {
 validUnits.put("字节", "Bytes");
 validUnits.put("bytes", "Bytes");
 validUnits.put("byte", "Bytes");
 validUnits.put("kb", "KB");
 validUnits.put("k", "KB");
 validUnits.put("兆", "MB");
 validUnits.put("mb", "MB");
 validUnits.put("m", "MB");
 validUnits.put("gb", "GB");
 validUnits.put("g", "GB");
 }
 /**
* 构造方法：指定了数字格式，初始所有属性为 NULL
*/
 public UnitsConversion() {
 super("########.##");
 numPart = null;
 result = null;
 unit = null;
 originalUnit = null;
 }
 /**
* 根据单位、数字大小按照常用的转换原则进行转换
* @param input
* @return 成功转换后的结果是非空字符串；若失败了，结果为空字符串
*/
 public String defaultConversion(String input) {
 analyzeString(input);
 if (result != null) {
 return result;
 }
 // 单位 Bytes
 if (unit.equals("Bytes")) {
 int numPart2int = numPart.intValue();
 / 输入大小与 1G 相差 0.5M 之内，返回 1GB
 if ((BYTES_MAX_SIZE - numPart2int) < (1024 * 1024) / 2) {
 return "1 GB";
 }
 // (0,1KB)
 if (numPart2int < 1024) {
 return numPart2int + " Bytes";
 }
 // [1KB,1023KB]
 if (numPart2int >= 1024 && numPart2int <= (1024 - 1) * 1024) {
 return format(numPart / 1024) + " KB";
 }
 // (1023KB,1GB)
 if (numPart2int > (1024 - 1) * 1024 && numPart2int < BYTES_MAX_SIZE) {
 return format(numPart / (1024 * 1024)) + " MB";
 } else
 result = "";
 return result;
 }
 if (unit.equals("KB")) {
 return "还没实现....";
 }
 if (unit.equals("MB")) {
 return "还没实现....";
 }
 if (unit.equals("GB")) {
 return "还没实现....";
 }
 result = "";
 return result;
 }
 /** * 把字符串的数字部分与单位分离，并对数字、单位的有效性进行检验， 若有非法状况，把结果赋值为 "" ，将其返回给用户 * * @param input
*/
 public void analyzeString(String input) {
 / 初步检验输入的字符串
 if (input == null || input.trim().length() < 2) {
 System.out.println("输入的字符串有误");
 result = "";
 return;
 }
 input = input.replaceAll(" ", "");
 int firstIndexOfUnit;
 // 单位的起始位置
 String strOfNum;
 // 数字部分的字符串
 / 从尾部开始遍历字符串
 for (int i = input.length() - 1; i >= 0; i--) {
 if (Character.isDigit(input.charAt(i))) {
 firstIndexOfUnit = i + 1;
 originalUnit = input.substring(firstIndexOfUnit,
 input.length()).toLowerCase();
 if (!isValidUnit(originalUnit)) {
 System.out.println("无效单位。");
 result = "";
 return;
 }
 unit = validUnits.get(originalUnit);
 strOfNum = input.substring(0, firstIndexOfUnit);
 numPart = double.parsedouble(strOfNum);
 if (!isValidNum(numPart, unit)) {
 System.out.println("文件大小非法");
 result = "";
 return;
 }
 if (numPart == 0) {
 result = "0 Bytes";
 return;
 }
 break;
 }
 }
 if (unit == null || numPart == null) {
 System.out.println("输入的字符串有误");
 result = "";
 return;
 }
 }
 /**
* 文件大小越界检查
* 
* @param num
* @param unit
* @return 在 1G 范围内（包括 1G），返回 true；否则返回 false */
 public Boolean isValidNum(double num, String unit) {
 if (num == null || num < 0 || num > BYTES_MAX_SIZE) {
 return false;
 }
 if (unit.equals("KB") && num > KB_MAX_SIZE) {
 return false;
 }
 if (unit.equals("MB") && num > MB_MAX_SIZE) {
 return false;
 }
 if (unit.equals("GB") && num > GB_MAX_SIZE) {
 return false;
 }
 return true;
 }
 /**
* 检查原始单位 originalUnit 是否有效
* 
* @param originalUnit
* @return 若 originalUnit 为空，那么会给他赋默认值 bytes ，并返回 true；<br>
* 若 originalUnit 是有效单位集合中之一，返回 true。
*/
 public Boolean isValidUnit(String originalUnit) {
 if (originalUnit == null || originalUnit.trim().length() < 1) {
 originalUnit = "bytes";
 return true;
 }
 for (String validUnit : validUnits.keySet()) {
 if (validUnit.equalsIgnoreCase(originalUnit)) {
 return true;
 }
 }
 return false;
 }
 //测试
 public static void main(String[] args) {
 System.out.println("-------------");
 for (int i = 1020 * 1024; i <= 1024 * 1111; i += 9) {
 String input = i + " ";
 System.out.println(input + " ---> "
 + new UnitsConversion().defaultConversion(input));
 }
 }
}

Java日期格式化及其使用例子

back

①. SimpleDateFormat 担当重任,怎样格式化都行

import java.util.Date;
import java.text.SimpleDateFormat;
public class Demo
{
 public static void main(String[] args)
 {
 Date now=new Date();
 SimpleDateFormat f=newSimpleDateFormat("今天是"+"yyyy 年 MM 月 dd 日 E kk 点 mm 分");
 System.out.println(f.format(now));
 f=new SimpleDateFormat("a hh 点 mm 分 ss 秒");
 System.out.println(f.format(now));
 }
}

②. 从字符串到日期类型的转换：

import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.GregorianCalendar;
import java.text.*;
publicclass Demo
{
 public static void main(String[] args)
 {
 String strDate="2005 年 04 月 22 日";
 //注意：SimpleDateFormat 构造函数的样式与 strDate 的样式必须相符
 SimpleDateFormat simpleDateFormat=new SimpleDateFormat("yyyy 年 MM 月 dd 日");
 //必须捕获异常
 try
 {
 Date date=simpleDateFormat.parse(strDate);
 System.out.println(date);
 }
 catch(ParseException px)
 {
 px.printStackTrace();
 }
 }
}

③. 将毫秒数换转成日期类型

import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.GregorianCalendar;
import java.text.*;
public class Demo
{
 public static void main(String[] args)
 {
 long now=System.currentTimeMillis();
 System.out.println("毫秒数："+now);
 Date dNow=new Date(now);
 System.out.println("日期类型："+dNow);
 }
}

④. 获取系统时期和时间，转换成 SQL 格式后更新到数据库

java.util.Date d=new java.util.Date();
//获取当前系统的时间
//格式化日期
new java.text.SimpleDateFormat s= new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateStr = s.format(d);
//转为字符串
// 使用 RS 更新数据库，仍然要用 rs.updateString，而不是 rs.updateDade。 rs.updateString("regtime",dateStr);
//regtime 字段为 datetime 类型的

⑤. 按本地时区输出当前日期

Date myDate = new Date();
System.out.println(myDate.toLocaleString());

输出结果为：
2003-5-30

⑥. 如何格式化小数

DecimalFormat df = new DecimalFormat(",###.00");
double aNumber = 33665448856.6568975;
String result = df.format(aNumber);
Sytem. out.println(result);

输出结果为：
33,665,448,856.66

其他：获取毫秒时间 System.currentTimeMillis();

⑦. 在数据库里的日期只以年-月-日的方式输出

// 定义日期格式：
SimpleDateFormat sdf = new SimpleDateFormat(yy-MM-dd);
// sql 语句为：

String sqlStr = "select bookDate from roomBook where bookDate between '2007-4-10' and '2007-4-25'";
// 输出：
System.out.println(df.format(rs.getDate("bookDate")));

java几个常用方法

字符串
①. 获取字符串的长度length()
②. 判断字符串的前缀或后缀与已知字符串是否相同前缀 startsWith(String s),后缀 endsWith(String s)
③. 比较两个字符串 equals(String s)
④. 把字符串转化为相应的数值 int 型 Integer.parseInt(字符串) long 型 Long.parseLong(字符串),float 型 Folat.valueOf(字符串).floatValue() double 型 Double.valueOf(字符串).doubleValue()
⑤. 将数值转化为字符串valueOf(数值)
⑥. 字符串检索:indexOf(Srting s) 从头开始检索,indexOf(String s ,int startpoint) 从 startpoint 处开始检索如果没有检索到，将返回-1
⑦. 得到字符串的子字符串：substring(int startpoint) 从 startpoint 处开始获取 substring(int start,int end) 从 start 到 end 中间的字符
⑧. 替换字符串中的字符,去掉字符串前后空格:replace(char old,char new) 用 new 替换 oldtrim()
⑨. 分析字符串:StringTokenizer(String s) 构造一个分析器，使用默认分隔字符（空格，换行，回车，Tab，进纸符）
- StringTokenizer(String s,String delim) delim 是自己定义的分隔符
- nextToken() 逐个获取字符串中的语言符号,
- boolean hasMoreTokens() 只要字符串还有语言符号将返回 true，否则返回 false
- countTokens() 得到一共有多少个语言符号

Java中的鼠标和键盘事件

①. 使用 MouseListener 借口处理鼠标事件

鼠标事件有 5 种：按下鼠标键，释放鼠标键，点击鼠标键，鼠标进入和鼠标退出,鼠标事件类型是 MouseEvent，主要方法有：

getX(),getY() 获取鼠标位置
getModifiers() 获取鼠标左键或者右键
getClickCount() 获取鼠标被点击的次数
getSource() 获取鼠标发生的事件源
事件源获得监视器的方法是 addMouseListener()，
移去监视器的方法是 removeMouseListener() 处理事件源发生的时间的事件的接口是 MouseListener 接口中有如下的方法 mousePressed(MouseEvent) 负责处理鼠标按下事件
mouseReleased(MouseEvent) 负责处理鼠标释放事件
mouseEntered(MouseEvent) 负责处理鼠标进入容器事件
mouseExited(MouseEvent) 负责处理鼠标离开事件
mouseClicked(MouseEvent) 负责处理点击事件

②. 使用 MouseMotionListener 接口处理鼠标事件

事件源发生的鼠标事件有 2 种：拖动鼠标和鼠标移动

鼠标事件的类型是 MouseEvent
事件源获得监视器的方法是 addMouseMotionListener()
处理事件源发生的事件的接口是 MouseMotionListener 接口中有如下的方法
mouseDragged() 负责处理鼠标拖动事件
mouseMoved() 负责处理鼠标移动事件

③. 控制鼠标的指针形状

setCursor(Cursor.getPreddfinedCursor(Cursor.鼠标形状定义)) 鼠标形状定义见（书 P 210）

④. 键盘事件

键盘事件源使用 addKeyListener 方法获得监视器,键盘事件的接口是 KeyListener 接口中有 3 个方法

public void keyPressed(KeyEvent e) 按下键盘按键
public void keyReleased(KeyEvent e) 释放键盘按键
public void keyTypde(KeyEvent e) 按下又释放键盘按键

判断字符是否属于中文

public class IsChineseOrEnglish {
 // GENERAL_PUNCTUATION 判断中文的“号
 // CJK_SYMBOLS_AND_PUNCTUATION 判断中文的。号
 // HALFWIDTH_AND_FULLWIDTH_FORMS 判断中文的，号
 public static Boolean isChinese(char c) {
 Character.UnicodeBlock ub = Character.UnicodeBlock.of(c);
 if (ub == Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS
 || ub == Character.UnicodeBlock.CJK_COMPATIBILITY_IDEOGRAPHS
 || ub == Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A
 || ub == Character.UnicodeBlock.GENERAL_PUNCTUATION
 || ub == Character.UnicodeBlock.CJK_SYMBOLS_AND_PUNCTUATION
 || ub == Character.UnicodeBlock.HALFWIDTH_AND_FULLWIDTH_FORMS){
 return true;
 }
 return false;
 }
 public static void isChinese(String strName) {
 char[] ch = strName.toCharArray();
 for (int i = 0; i < ch.length; i++) {
 char c = ch[i];
 if(isChinese(c)==true){
 System.out.println(isChinese(c));
 return;
 } else{
 System.out.println(isChinese(c));
 return ;
 }
 }
 }
 public static void main(String[] args){
 isChinese("zhongguo");
 isChinese("中国");
 }
}

去掉字符串中重复的子字符串

/**
* 去掉字符串中重复的子字符串
* @param str
* @return String
*/
private static String removeSameString(String str)
{
 Set<String> mLinkedSet = new LinkedHashSet<String>();
 String[] strArray = str.split(" ");
 StringBuffer sb = new StringBuffer();
 for (int i = 0; i < strArray.length; i++)
 {
 if (!mLinkedSet.contains(strArray[i]))
 {
 mLinkedSet.add(strArray[i]);
 sb.append(strArray[i] + " ");
 }
 }
 System.out.println(mLinkedSet);
 return sb.toString().substring(0, sb.toString().length() - 1);
}

将指定 byte 数组以 16 进制的形式打印到控制台

/**
* 将指定 byte 数组以 16 进制的形式打印到控制台
* @param hint String
* @param b byte[]
* @return void
*/
public static void printHexString(String hint, byte[] b)
{
 System.out.print(hint);
 for (int i = 0; i < b.length; i++)
 {
 String hex = Integer.toHexString(b[i] & 0xFF);
 if (hex.length() == 1)
 {
 hex = '0' + hex;
 }
 System.out.print(hex.toUpperCase() + " ");
 }
 System.out.println("");
}

获得任意一个整数的阶乘，递归

/**
* 获得任意一个整数的阶乘，递归
* @param n
* @return n!
*/
public static int factorial(int n)
{
 if (n == 1)
 {
 return 1;
 }
 return n * factorial(n - 1);
}

拷贝一个目录或者文件到指定路径下

/**
* 拷贝一个目录或者文件到指定路径下
* @param source
* @param target
*/
public static void copy(File source, File target)
{
 File tarpath = new File(target, source.getName());
 if (source.isDirectory())
 {
 tarpath.mkdir();
 File[] dir = source.listFiles();
 for (int i = 0; i < dir.length; i++) {
 copy(dir[i], tarpath);
 }
 } else
 {
 try
 {
 InputStream is = new FileInputStream(source);
 OutputStream os = new FileOutputStream(tarpath);
 byte[] buf = new byte[1024];
 int len = 0;
 while ((len = is.read(buf)) != -1)
 {
 os.write(buf, 0, len);
 }
 is.close();
 os.close();
 }
 catch (FileNotFoundException e)
 {
 e.printStackTrace();
 }
 catch (IOException e)
 {
 e.printStackTrace();
 }
 }
}

简单的 txt 转换 xml

package cn.wuliaokankan;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.StringTokenizer;
public class TxtToXml {
 private String strTxtFileName;
 private String strXmlFileName;
 public TxtToXml() {
 strTxtFileName = new String();
 strXmlFileName = new String();
 }
 public void createXml(String strTxt, String strXml) {
 strTxtFileName = strTxt;
 strXmlFileName = strXml;
 String strTmp;
 try {
 BufferedReader inTxt = new BufferedReader(new FileReader( strTxtFileName));
 BufferedWriter outXml = new BufferedWriter(new FileWriter(
 strXmlFileName));
 outXml.write("<?xml version= "1.0" encoding="gb2312"?>");
 outXml.newLine();
 outXml.write("<people>");
 while ((strTmp = inTxt.readLine()) != null) {
 StringTokenizer strToken = new StringTokenizer(strTmp, "，");
 String arrTmp[];
 arrTmp = new String[3];
 for (int i = 0; i < 3; i++)
 arrTmp[i] = new String("");
 int index = 0;
 outXml.newLine();
 outXml.write(" <students>");
 while (strToken.hasMoreElements()) {
 strTmp = (String) strToken.nextElement();
 strTmp = strTmp.trim();
 arrTmp[index++] = strTmp;
 }
 outXml.newLine();
 outXml.write("
<name>" + arrTmp[0] + "</name>");
 outXml.newLine();
 outXml.write("
<sex>" + arrTmp[1] + "</sex>");
 outXml.newLine();
 outXml.write("
<age>" + arrTmp[2] + "</age>");
 outXml.newLine();
 outXml.write("
</students>");
 }
 outXml.newLine();
 outXml.write("</people>");
 outXml.flush();
 }
 catch (Exception e) {
 e.printStackTrace();
 }
 }
 public static void main(String[] args) {
 String txtName = "testtxt.txt";
 String xmlName = "testxml.xml";
 TxtToXml thisClass = new TxtToXml();
 thisClass.createXml(txtName, xmlName);
 }
}

字母排序(A-Z)(先大写，后小写)

import java.util.Arrays;
import java.util.Comparator;
public class SortTest
{
 public static void main(String args[])
 {
 char[] chs = {'f', 'F', 'K', 'A', 'a', 'j', 'z'};
 chs = sortChars(chs, false);
 for (char c: chs)
 {
 System.out.println(c);
 }
 }
 /**
* 对给定的字符数组进行字典排序
* @param chs 目标字符数组
* @param upperFisrt 大写字母是否在前
* @return 排序后的字符数组
*/
 public static char[] sortChars(char[] chs, final Boolean upperFisrt)
 {
 Character[] srcArray = new Character[chs.length];
 char[] retArray = new char[chs.length];
 int index = 0;
 for (char ch: chs)
 {
 srcArray[index++] = ch;
 }
 Arrays.sort(srcArray, new Comparator<Character>()
 {
 public int compare(Character c1, Character c2)
 {
 char ch1 = Character.toUpperCase(c1);
 char ch2 = Character.toUpperCase(c2);
 if(ch1 == ch2)
 {
 int tempRet = c1.charValue() - c2.charValue();
 return upperFisrt? tempRet: -tempRet;
 } else
 {
 return ch1 - ch2;
 }
 }
 }
 );
 index = 0;
 for (char ch: srcArray)
 {
 retArray[index++] = ch;
 }
 return retArray;
 }
}

列出某文件夹及其子文件夹下面的文件，并可根据扩展名过滤

/**
* 列出某文件夹及其子文件夹下面的文件，并可根据扩展名过滤
* @param path
*/
public static void list(File path)
{
 if (!path.exists())
 {
 System.out.println("文件名称不存在!");
 } else
 {
 if (path.isFile())
 {
 if (path.getName().toLowerCase().endsWith(".pdf")
 || path.getName().toLowerCase().endsWith(".doc")
 || path.getName().toLowerCase().endsWith(".html")
 || path.getName().toLowerCase().endsWith(".htm"))
 {
 System.out.println(path);
 System.out.println(path.getName());
 }
 } else
 {
 File[] files = path.listFiles();
 for (int i = 0; i < files.length; i++)
 {
 list(files[i]);
 }
 }
 }
}

字符串匹配的算法

public String getMaxMatch(String a,String b) {
 StringBuffer tmp = new StringBuffer();
 String maxString = "";
 int max = 0;
 int len = 0;
 char[] aArray = a.toCharArray();
 char[] bArray = b.toCharArray();
 int posA = 0;
 int posB = 0;
 while(posA<aArray.length-max) {
 posB = 0;
 while(posB<(bArray.length-max)) {
 if(aArray[posA]==bArray[posB]) {
 len = 1;
 tmp = new StringBuffer();
 tmp.append(aArray[posA]);
 while((posA+len<aArray.length)&&(posB+len<bArray.length)&&(aArray[posA+len]==bArray[posB+len]))
 {
 tmp.append(aArray[posA+len]);
 len++;
 }
 if(len>max) {
 max = len;
 maxString = tmp.toString();
 }
 }
 posB++;
 }
 posA++;
 }
 return maxString;
}

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