JAVA常用代码

1.得到当前月的第一天和最后一天,注意3是4月份，从零开始
     Calendar    c    =    Calendar.getInstance();
          c.set(Calendar.YEAR,    2007);
          c.set(Calendar.MONTH,    3);
          System.out.println(c.getActualMaximum(c.DAY_OF_MONTH));
          System.out.println(c.getActualMinimum(c.DAY_OF_MONTH));

2.十六进制的转换

String st = "this is roger";
// hex
for(int i = 0; i<st.length(); i++){
System.out.println();
int ch=(int)st.charAt( i );
String s4="00"+Integer.toHexString( ch );
System.out.println(i + "output->"+s4); // String to Hex

//back String
int intVal = Integer.parseInt(s4, 16);
char charVal = (char) intVal;
System.out.println("The character is: "+charVal);

}

int temp = 1234567;
String hexString = Integer.toHexString(temp);
System.out.println( "hexString = " + hexString );
String str = Integer.toString(Integer.parseInt(hexString, 16));
System.out.println( "str = " + str );

/ 转化十六进制编码为字符串
public static String toStringHex(String s)
{
byte[] baKeyword = new byte[s.length()/2];
for(int i = 0; i < baKeyword.length; i++)
{
try
{
baKeyword[i] = (byte)(0xff & Integer.parseInt(s.substring(i*2, i*2+2),16));
}
catch(Exception e)
{
e.printStackTrace();
}
}

try
{
s = new String(baKeyword, "utf-8");//UTF-16le:Not
}
catch (Exception e1)
{
e1.printStackTrace();
}
return s;
}

public static void main(String[] args) {
System.out.println(encode("中文"));
System.out.println(decode(encode("中文")));
}
/*
* 16进制数字字符集
*/
private static String hexString="0123456789ABCDEF";
/*
* 将字符串编码成16进制数字,适用于所有字符（包括中文）
*/
public static String encode(String str)
{
//根据默认编码获取字节数组
byte[] bytes=str.getBytes();
StringBuilder sb=new StringBuilder(bytes.length*2);
//将字节数组中每个字节拆解成2位16进制整数
for(int i=0;i<bytes.length;i++)
{
sb.append(hexString.charAt((bytes[i]&0xf0)>>4));
sb.append(hexString.charAt((bytes[i]&0x0f)>>0));
}
return sb.toString();
}
/*
* 将16进制数字解码成字符串,适用于所有字符（包括中文）
*/
public static String decode(String bytes)
{
ByteArrayOutputStream baos=new ByteArrayOutputStream(bytes.length()/2);
//将每2位16进制整数组装成一个字节
for(int i=0;i<bytes.length();i+=2)
baos.write((hexString.indexOf(bytes.charAt(i))<<4 |hexString.indexOf(bytes.charAt(i+1))));
return new String(baos.toByteArray());
}

或

String str="中";
char c=(char)str.charAt(0);
System.out.println(c+"转换为16进制为："+Integer.toString(c,16));
System.out.println("16进制转换为字符串为:"+(char)Integer.valueOf(Integer.toString(c, 16),16).intValue());
public class testcolor {

private 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);
// System.out.println(ret<<8);
return ret;
}
/**
* @param src
* @return
*/
/*private static byte[] HexString2Bytes(String src) {
byte[] ret = new byte[6];
byte[] tmp = src.getBytes();

for (int i = 0; i < 3; i++) {
ret[i] = uniteBytes(tmp[i * 2], tmp[i * 2 + 1]);
}
return ret;
}
;*/

public static byte[] HexString2Bytes(String src)
{ byte[] ret = new byte[6];
byte[] tmp = src.getBytes(); for(int i=0; i<6; ++i ){ ret[i] = uniteBytes(tmp[i*2], tmp[i*2+1]); } return ret; }


/**
* @param args
*/
public static void main(String[] args) {
// TODO 自动生成方法存根

String s="ff22ee";
Number ss;
byte[] ret = new byte[6];
Integer i=new Integer(ret[0]);

ret = HexString2Bytes(s) ;

int c=((ret[2]<<8|ret[1]<<8|ret[0])|0xff000000);
//Color cc=new Color(c);
// System.out.println(cc.getRed()+":::"+cc.getBlue()+":::"+cc.getGreen());
}

}

将IP地址转为10进制数，使用小端模式
public static int parseIPNUmber(String ipNumberStr)
             throws IllegalArgumentException {
         int result = 0;

         if (ipNumberStr == null) {
             throw new IllegalArgumentException();
         }

         StringTokenizer tokenizer = new StringTokenizer(ipNumberStr, ".");
         try {
             String tmp = ipNumberStr;

             // get the 3 first numbers
             int offset = 0;
             for (int i = 0; i < 3; i++) {

                 // get the position of the first dot
                 int index = tmp.indexOf(".");

                 // if there is not a dot then the ip string representation is
                 // not compliant to the decimal-dotted notation.
                 if (index != -1) {

                     // get the number before the dot and convert it into
                     // an integer.
                     String numberStr = tmp.substring(0, index);
                     int number = Integer.parseInt(numberStr);
                     if ((number < 0) || (number > 255)) {
                         throw new IllegalArgumentException(ipNumberStr);
                     }

                     result += number << offset;
                     offset += 8;
                     tmp = tmp.substring(index + 1);
                 } else {
                     throw new IllegalArgumentException(ipNumberStr);
                 }
             }

             // the remaining part of the string should be the last number.
             if (tmp.length() > 0) {
                 int number = Integer.parseInt(tmp);
                 if ((number < 0) || (number > 255)) {
                     throw new IllegalArgumentException(ipNumberStr);
                 }

                 result += number << offset;

             } else {
                 throw new IllegalArgumentException(ipNumberStr);
             }
         }
         catch (NoSuchElementException ex) {
             throw new IllegalArgumentException(ipNumberStr);
         }
         catch (NumberFormatException ex) {
             throw new IllegalArgumentException(ipNumberStr);
         }

         return result;
     }
将10进制数字转为IP地址
public static String toip(int mIPNumber) {
         StringBuffer result = new StringBuffer();
         int temp;

         temp = mIPNumber & 0x000000FF;
         result.append(temp);
         result.append(".");

         temp = (mIPNumber >> & 0x000000FF;
         result.append(temp);
         result.append(".");

         temp = (mIPNumber >> 16) & 0x000000FF;
         result.append(temp);
         result.append(".");

         temp = (mIPNumber >> 24) & 0x000000FF;
         result.append(temp);

         return result.toString();
     }
掩码和网络地址的转换 例如 /24就是255.255.255.0

public static int computeNetworkPrefixFromMask(int mask) {
         int result = 0;
         int tmp = mask;

         while ((tmp & 0x00000001) == 0x00000001) {
             result++;
             tmp = tmp >>> 1;
         }

         if (tmp != 0) {
             return -1;
         }
         return result;
     }

     public static int computeMaskFromNetworkPrefix(int prefix)

     {
         int subnet = 0;
         for (int i = 0; i < prefix; i++) {
             subnet = subnet << 1;
             subnet += 1;
         }
         return subnet;
     }
例如   System.out.println(toip(computeMaskFromNetworkPrefix(20)));
是255.255.15.0

判断两个IP是不是在一个子网内

public static boolean isIPAddressInRange (int address1,int adress2,int subnet)
     {
         int result1 = address1 & subnet;
         int result2 =adress2 & subnet;

         return result1 == result2;
     }

读取classes的下面的文件
      TestDOMParsing.class.getResourceAsStream("/MSG-response.xml");
      返回输入流


web工程不必这样做
     使用ServletContext.getResourceAsStream()就可以.
sun的文档这样说得
Returns a URL to the resource that is mapped to a specified path. The path must begin with a "/" and is interpreted as relative to the current context root.
This method allows the servlet container to make a resource available to servlets from any source. Resources can be located on a local or remote file system, in a #base, or in a .war file.

简单类型的排序

简单类型不外是byte, char, short, int, long, float, double等数据类型， 这些类型不能放在聚集中，只能使用数组。java.util.Arrays方法提供了对这些类型的sort方法（实际上还有很多其他有用的方法），下面是对一个简单的int数组排序：

        int[] arr = {2, 3, 1,10,7,4};


        System.out.print("before sort: ");

        for (int i = 0; i< arr.length; i++)

            System.out.print(arr[i] + " ");

        System.out.println();      


        Arrays.sort(arr);

        System.out.print("after sort: ");

        for (int i = 0; i< arr.length; i++)

            System.out.print(arr[i] + " ");

        System.out.println();      

输出结果：

before sort: 2 3 1 10 7 4

after sort: 1 2 3 4 7 10

对象的排序

对象可以放在数组里，同样调用Arrays.sort(Object[] arr)即可；也可以放到聚集里，用java.util.Collections的sort(List list)。注意不是list必须实现List接口而不仅仅是Collection接口。

但是这个类必须实现了java.lang.Comparable接口。这个接口只有一个方法：int compartTo(Object o)，当本对象比传入的对象大时，返回一个正整数。 以类Programmer为例：

class Programmer implements Comparable{

     private String name;

     private String language;

     private double pay;

   

     public Programmer(String name, String language, double pay) {

        this.name = name;

        this.language = language;

        this.pay = pay;

     }


     public int compareTo(Object o) {

        Programmer other = (Programmer)o;

        return (int)pay - (int)other.pay;

     }


     public String toString(){

        return "{name: " + name + ", language: " + language + ", money: " + pay + "}";

     }

}

对其进行排序：

        ArrayList list = new ArrayList();

        list.add(new Programmer("张三", "C", 12000));

        list.add(new Programmer("李四", "Java", 200));

        list.add(new Programmer("王五", "C++", 5000));

        list.add(new Programmer("钱六", "VB", 3000));

        System.out.println("before sort: " + list);

        Collections.sort(list);

        System.out.println("after sort: " + list);   

输出：

before sort: [{name: 张三, language: C, money: 12000.0}, {name: 李四, language: Java, money: 200.0}, {name: 王五, language: C++, money: 5000.0}, {name: 钱六, language: VB, money: 3000.0}]

after sort: [{name: 李四, language: Java, money: 200.0}, {name: 钱六, language: VB, money: 3000.0}, {name: 王五, language: C++, money: 5000.0}, {name: 张三, language: C, money: 12000.0}]