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blog名称:邢红瑞的blog
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 [java语言]java常用容易忽略的代码
原创空间, 文章收藏, 网上资源, 软件技术, 电脑与网络
邢红瑞 发表于 2007/3/26 18:04:18 |
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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";// hexfor(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 Stringint 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 >> 8) & 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 database, 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}] |
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回复:java常用容易忽略的代码
原创空间, 文章收藏, 网上资源, 软件技术, 电脑与网络
tone发表评论于2007/3/27 9:00:21 |
| 不对啊!
我试了今年3月份,但是打出来的结果是错的
Calendar c = Calendar.getInstance(); c.set(c.YEAR, 2007); c.set(c.MONTH, 3); System.out.println(c.getActualMaximum(c.DAY_OF_MONTH)); System.out.println(c.getActualMinimum(c.DAY_OF_MONTH));
结果:
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