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1. 新建一个记事本,后缀名是 .java ;然后在里面写一段java的代码,如图:
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2.把写好的java文件丢进D盘,就是第一步给出的那个class文件;
3. 打开dos界面 开始-〉运行-〉cmd-〉 这个是命令行模式,选择D盘,如图:
4.选择D盘之后,在命令提示符中输入“javac 文件名.java”,我的文件名为java,所以输入javac java.java然后回车,等待编译。这时候你就会发现它提示说javac不是内部文件。接下来就是java环境变量设置的问题了;
5.下载一个jdk执行默认安装。例如我下的jdk版本是: jdk-6u10-rc2-bin-b32-windows-i586-p-12_sep_2008.exe;
6.配置环境:右击我的电脑点属性,进去点高级就能看到环境变量。点进去就能设置你的系统变量了,如图:
6-1。变量名:classpath 变量值:(.;C:\Program Files\Java\jdk1.6.0_10\lib;)括号里面都是 (主要我们在编译运行程序的时候通过classpath可以帮助我们找到一些需要的系统类,“.”号是表示当前路径;“;”号是用来隔开多个变量值,如果你的系统里面已经有classpath环 境变量,就不用新建了,直接加“;”号,在后面加新值);如图所示
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
public class IOTest {
public static void main(String[] args) {
String str = "123\r\n456";
writeFile(str);//写
String str1 = readFile();//读
System.out.println(str1);
}
/**
* 传递写的内容
* @param str
*/
static void writeFile(String str) {
try {
File file = new File("d:\\file.txt");
if(file.exists()){//存在
file.delete();//删除再建
file.createNewFile();
}else{
file.createNewFile();//不存在直接创建
}
FileWriter fw = new FileWriter(file);//文件写IO
fw.write(str);
fw.flush();
fw.close();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 返回读取的内容
* @return
*/
static String readFile() {
String str = "", temp = null;
try {
File file = new File("d:\\file.txt");
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);//文件读IO
while((temp = br.readLine())!=null){//读到结束为止
str += (temp+"\n");
}
br.close();
fr.close();
} catch (IOException e) {
e.printStackTrace();
}
return str;
}
}
刚写的,够朋友好好学习一下啦,呵呵
多多看API,多多练习
package filewriter;
import java.io.FileWriter;
import java.io.IOException;
public class IOExceptionDemo {
private static final String LINE_SEPARATOR = System.getProperty("line.separator");
public static void main(String[] args) {
FileWriter fw = null;
try {
fw = new FileWriter("k:\\Demo.txt", true);
fw.write("hello" + LINE_SEPARATOR + "world!");
} catch (Exception e) {
System.out.println(e.toString());
} finally {
if (fw != null)
try {
fw.close();
} catch (IOException e) {
throw new RuntimeException("关闭失败!");
}
}
}
}
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
/**
文件名:FileEncrypter.java
JDK:1.40以上
说明:文件加密
加密方法:三重DES加密
加密过程:对选中的文件加密后在同文件夹下生成一个增加了".tdes"
扩展名的加密文件
解密过程:对选中的加密文件(必须有".tdes"扩展名)进行解密
*/
public class FileEncrypter extends JFrame{
public static final int WIDTH = 550;
public static final int HEIGHT = 200;
public static void main(String args[]) {
FileEncrypter fe = new FileEncrypter();
fe.show();
}
FileEncrypter(){
this.setSize(WIDTH,HEIGHT);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setResizable(false);
Toolkit tk = Toolkit.getDefaultToolkit();
Dimension screenSize = tk.getScreenSize();
this.setLocation((screenSize.width - WIDTH)/2,
(screenSize.height - HEIGHT)/2);
this.setTitle("文件加密器(TriDES)");
Container c = this.getContentPane();
c.setLayout( new FlowLayout());
final FilePanel fp = new FilePanel("文件选择");
c.add(fp);
final KeyPanel pp = new KeyPanel("密码");
c.add(pp);
JButton jbE = new JButton("加密");
c.add(jbE);
jbE.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event){
File file = new File(fp.getFileName());
if (file.exists())
encrypt(file.getAbsoluteFile(),pp.getKey());
else
JOptionPane.showMessageDialog(
null,"请选择文件!","提示",JOptionPane.OK_OPTION);
}
});
JButton jbD = new JButton("解密");
c.add(jbD);
jbD.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event){
File file = new File(fp.getFileName());
if (file.exists())
decrypt(file.getAbsoluteFile(),pp.getKey());
else
JOptionPane.showMessageDialog(
null,"请选择文件!","提示",JOptionPane.OK_OPTION);
}
});
}
/**
加密函数
输入:
要加密的文件,密码(由0-F组成,共48个字符,表示3个8位的密码)如:
AD67EA2F3BE6E5ADD368DFE03120B5DF92A8FD8FEC2F0746
其中:
AD67EA2F3BE6E5AD DES密码一
D368DFE03120B5DF DES密码二
92A8FD8FEC2F0746 DES密码三
输出:
对输入的文件加密后,保存到同一文件夹下增加了".tdes"扩展名的文件中。
*/
private void encrypt(File fileIn,String sKey){
try{
if(sKey.length() == 48){
byte[] bytK1 = getKeyByStr(sKey.substring(0,16));
byte[] bytK2 = getKeyByStr(sKey.substring(16,32));
byte[] bytK3 = getKeyByStr(sKey.substring(32,48));
FileInputStream fis = new FileInputStream(fileIn);
byte[] bytIn = new byte[(int)fileIn.length()];
for(int i = 0;iFILEIN.LENGTH();I++){
bytIn[i] = (byte)fis.read();
}
//加密
byte[] bytOut = encryptByDES(encryptByDES(
encryptByDES(bytIn,bytK1),bytK2),bytK3);
String fileOut = fileIn.getPath() + ".tdes";
FileOutputStream fos = new FileOutputStream(fileOut);
for(int i = 0;iBYTOUT.LENGTH;I++){
fos.write((int)bytOut[i]);
}
fos.close();
JOptionPane.showMessageDialog(
this,"加密成功!","提示",JOptionPane.OK_OPTION);
}else
JOptionPane.showMessageDialog(
this,"密码长度必须等于48!","错误信息",JOptionPane.ERROR_MESSAGE);
}catch(Exception e){
e.printStackTrace();
}
}
/**
解密函数
输入:
要解密的文件,密码(由0-F组成,共48个字符,表示3个8位的密码)如:
AD67EA2F3BE6E5ADD368DFE03120B5DF92A8FD8FEC2F0746
其中:
AD67EA2F3BE6E5AD DES密码一
D368DFE03120B5DF DES密码二
92A8FD8FEC2F0746 DES密码三
输出:
对输入的文件解密后,保存到用户指定的文件中。
*/
private void decrypt(File fileIn,String sKey){
try{
if(sKey.length() == 48){
String strPath = fileIn.getPath();
if(strPath.substring(strPath.length()-5).toLowerCase().equals(".tdes"))
strPath = strPath.substring(0,strPath.length()-5);
else{
JOptionPane.showMessageDialog(
this,"不是合法的加密文件!","提示",JOptionPane.OK_OPTION);
return;
}
JFileChooser chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
chooser.setSelectedFile(new File(strPath));
//用户指定要保存的文件
int ret = chooser.showSaveDialog(this);
if(ret==JFileChooser.APPROVE_OPTION){
byte[] bytK1 = getKeyByStr(sKey.substring(0,16));
byte[] bytK2 = getKeyByStr(sKey.substring(16,32));
byte[] bytK3 = getKeyByStr(sKey.substring(32,48));
FileInputStream fis = new FileInputStream(fileIn);
byte[] bytIn = new byte[(int)fileIn.length()];
for(int i = 0;iFILEIN.LENGTH();I++){
bytIn[i] = (byte)fis.read();
}
//解密
byte[] bytOut = decryptByDES(decryptByDES(
decryptByDES(bytIn,bytK3),bytK2),bytK1);
File fileOut = chooser.getSelectedFile();
fileOut.createNewFile();
FileOutputStream fos = new FileOutputStream(fileOut);
for(int i = 0;iBYTOUT.LENGTH;I++){
fos.write((int)bytOut[i]);
}
fos.close();
JOptionPane.showMessageDialog(
this,"解密成功!","提示",JOptionPane.OK_OPTION);
}
}else
JOptionPane.showMessageDialog(
this,"密码长度必须等于48!","错误信息",JOptionPane.ERROR_MESSAGE);
}catch(Exception e){
JOptionPane.showMessageDialog(
this,"解密失败,请核对密码!","提示",JOptionPane.OK_OPTION);
}
}
/**
用DES方法加密输入的字节
bytKey需为8字节长,是加密的密码
*/
private byte[] encryptByDES(byte[] bytP,byte[] bytKey) throws Exception{
DESKeySpec desKS = new DESKeySpec(bytKey);
SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
SecretKey sk = skf.generateSecret(desKS);
Cipher cip = Cipher.getInstance("DES");
cip.init(Cipher.ENCRYPT_MODE,sk);
return cip.doFinal(bytP);
}
/**
用DES方法解密输入的字节
bytKey需为8字节长,是解密的密码
*/
private byte[] decryptByDES(byte[] bytE,byte[] bytKey) throws Exception{
DESKeySpec desKS = new DESKeySpec(bytKey);
SecretKeyFactory skf = SecretKeyFactory.getInstance("DES");
SecretKey sk = skf.generateSecret(desKS);
Cipher cip = Cipher.getInstance("DES");
cip.init(Cipher.DECRYPT_MODE,sk);
return cip.doFinal(bytE);
}
/**
输入密码的字符形式,返回字节数组形式。
如输入字符串:AD67EA2F3BE6E5AD
返回字节数组:{173,103,234,47,59,230,229,173}
*/
private byte[] getKeyByStr(String str){
byte[] bRet = new byte[str.length()/2];
for(int i=0;iSTR.LENGTH()
Integer itg =
new Integer(16*getChrInt(str.charAt(2*i)) + getChrInt(str.charAt(2*i+1)));
bRet[i] = itg.byteValue();
}
return bRet;
}
/**
计算一个16进制字符的10进制值
输入:0-F
*/
private int getChrInt(char chr){
int iRet=0;
if(chr=="0".charAt(0)) iRet = 0;
if(chr=="1".charAt(0)) iRet = 1;
if(chr=="2".charAt(0)) iRet = 2;
if(chr=="3".charAt(0)) iRet = 3;
if(chr=="4".charAt(0)) iRet = 4;
if(chr=="5".charAt(0)) iRet = 5;
if(chr=="6".charAt(0)) iRet = 6;
if(chr=="7".charAt(0)) iRet = 7;
if(chr=="8".charAt(0)) iRet = 8;
if(chr=="9".charAt(0)) iRet = 9;
if(chr=="A".charAt(0)) iRet = 10;
if(chr=="B".charAt(0)) iRet = 11;
if(chr=="C".charAt(0)) iRet = 12;
if(chr=="D".charAt(0)) iRet = 13;
if(chr=="E".charAt(0)) iRet = 14;
if(chr=="F".charAt(0)) iRet = 15;
return iRet;
}
}
/**
文件选择组件。
*/
class FilePanel extends JPanel{
FilePanel(String str){
JLabel label = new JLabel(str);
JTextField fileText = new JTextField(35);
JButton chooseButton = new JButton("浏览...");
this.add(label);
this.add(fileText);
this.add(chooseButton);
clickAction ca = new clickAction(this);
chooseButton.addActionListener(ca);
}
public String getFileName(){
JTextField jtf = (JTextField)this.getComponent(1);
return jtf.getText();
}
private class clickAction implements ActionListener{
clickAction(Component c){
cmpt = c;
}
public void actionPerformed(ActionEvent event){
JFileChooser chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
int ret = chooser.showOpenDialog(cmpt);
if(ret==JFileChooser.APPROVE_OPTION){
JPanel jp = (JPanel)cmpt;
JTextField jtf = (JTextField)jp.getComponent(1);
jtf.setText(chooser.getSelectedFile().getPath());
}
}
private Component cmpt;
}
}
/**
密码生成组件。
*/
class KeyPanel extends JPanel{
KeyPanel(String str){
JLabel label = new JLabel(str);
JTextField fileText = new JTextField(35);
JButton chooseButton = new JButton("随机产生");
this.add(label);
this.add(fileText);
this.add(chooseButton);
clickAction ca = new clickAction(this);
chooseButton.addActionListener(ca);
}
//返回生成的密码(48个字符长度)
public String getKey(){
JTextField jtf = (JTextField)this.getComponent(1);
return jtf.getText();
}
private class clickAction implements ActionListener{
clickAction(Component c){
cmpt = c;
}
public void actionPerformed(ActionEvent event){
try{
KeyGenerator kg = KeyGenerator.getInstance("DES");
kg.init(56);
Key ke = kg.generateKey();
byte[] bytK1 = ke.getEncoded();
ke = kg.generateKey();
byte[] bytK2 = ke.getEncoded();
ke = kg.generateKey();
byte[] bytK3 = ke.getEncoded();
JPanel jp = (JPanel)cmpt;
JTextField jtf = (JTextField)jp.getComponent(1);
jtf.setText(getByteStr(bytK1)+getByteStr(bytK2)+getByteStr(bytK3));
}catch(Exception e){
e.printStackTrace();
}
}
private String getByteStr(byte[] byt){
String strRet = "";
for(int i=0;iBYT.LENGTH;I++){
//System.out.println(byt[i]);
strRet += getHexValue((byt[i]240)/16);
strRet += getHexValue(byt[i]15);
}
return strRet;
}
private String getHexValue(int s){
String sRet=null;
switch (s){
case 0: sRet = "0";break;
case 1: sRet = "1";break;
case 2: sRet = "2";break;
case 3: sRet = "3";break;
case 4: sRet = "4";break;
case 5: sRet = "5";break;
case 6: sRet = "6";break;
case 7: sRet = "7";break;
case 8: sRet = "8";break;
case 9: sRet = "9";break;
case 10: sRet = "A";break;
case 11: sRet = "B";break;
case 12: sRet = "C";break;
case 13: sRet = "D";break;
case 14: sRet = "E";break;
case 15: sRet = "F";
}
return sRet;
}
private Component cmpt;
}
}
myeclipse编写java代码的步骤如下:
1.新建一个工程,取任意名字。
2.在工程目录的src目录下,创建一个java文件,如下图,名字以小写开头,后跟字母数字或者下划线。
3.打开刚才创建的java代码,就可以进行编写代码了。
只要自己的电脑安装了jdk环境,任何地方都可以进行java代码的编写的,记事本也可以。