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java怎么用代码实现 java编写代码
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java平方根用代码怎么实现？
java.lang.Math.sqrt(double a) 返回正确舍入java怎么用代码实现的一个double值java怎么用代码实现的正平方根。
相关问答
Q1: 怎么用java实现html代码
ava要运行html代码，需要运行在服务器端，也就是servlet容器中，经过容器编译解析，返回html静态内容，示例如下：
在servlet里面写就可以了
引入一系列包
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
public class Servlet1 extends HttpServlet {
public void doGet(ServletRequest req,ServletResponse res)throws ServletException, IOException{try{PrintWriter pw=res.getWriter();//在浏览器输出需要
pw.println("scriptscript");}catch(exception e){="" e.printstacktrace();="" 为发现调试错误}}}=""
Q2: 请用java代码实现如下方法
//供参考，代码应该没问题，难点主要是在如何匹配连续字符串，这点有小技巧
public class TestBaiduKnow {
public static void main(String args[]) throws Exception {
String s = "Sdabcdk3abcdabcdgg3abcdabcdabcd55fg";
char[] in = s.toCharArray();
char[] out = "abcd".toCharArray();
int cnt = 0;
cnt = maxfleg(in, out);
System.out.println("出现次数： " + cnt);
}
private static int maxfleg(char[] inputstr, char[] outputstr) {
String s = "";
String s2 = "";
for (int i = 0; i outputstr.length; i++)
s2 += outputstr[i];
int cnt = 0;
int maxcnt = 0;
for (int i = 0; i inputstr.length - 4; i++) {
for (int j = i; j i + 4; j++)
s += inputstr[j];
if (s.equals(s2)) {
cnt += 1;
i += 3;
if (cnt maxcnt)
maxcnt = cnt;
} else
cnt = 0;
s = "";
}
return maxcnt;
}
}
Q3: 利用java编写代码实现如下功能，需要全部代码
很简单的应用，为了节省字数，代码注释我就不加了
首先是显示层，LoinWindow：
import java.awt.FlowLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;
public class LoinWindow extends JFrame implements ActionListener, FocusListener {
private JPanel mainPanel, namePanel, btnPanel;
private JTextField tfName, tfPsd;
private JButton btnLogin, btnCancel;
private static final int WIDTH = 300;
private static final int HEIGHT = 200;
private LoginService service = new LoginService();
public LoinWindow() {
super("登录窗体");
}
public void launch() {
setSize(WIDTH, HEIGHT);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
GridLayout mainLayout = new GridLayout(2, 1);
mainLayout.setVgap(10);
mainPanel = new JPanel(mainLayout);
GridBagLayout nameLayout = new GridBagLayout();
namePanel = new JPanel(nameLayout);
namePanel.setBorder(new EmptyBorder(10, 10, 10, 10));
JLabel nameLabel = new JLabel("姓名：");
tfName = new JTextField();
JLabel psdLabel = new JLabel("密码：");
tfPsd = new JTextField();
JLabel blank = new JLabel(" ");
namePanel.add(nameLabel);
namePanel.add(tfName);
namePanel.add(blank);
namePanel.add(psdLabel);
namePanel.add(tfPsd);
GridBagConstraints s = new GridBagConstraints();
s.fill = GridBagConstraints.BOTH;
s.gridwidth = 1;
s.weightx = 0;
s.weighty = 0;
nameLayout.setConstraints(nameLabel, s);
s.gridwidth = 0;
s.weightx = 1;
s.weighty = 0;
nameLayout.setConstraints(tfName, s);
s.gridwidth = 0;
s.weightx = 4;
s.weighty = 0;
nameLayout.setConstraints(blank, s);
s.gridwidth = 1;
s.weightx = 0;
s.weighty = 0;
nameLayout.setConstraints(psdLabel, s);
s.gridwidth = 3;
s.weightx = 1;
s.weighty = 0;
nameLayout.setConstraints(tfPsd, s);
FlowLayout btnLayout = new FlowLayout();
btnLayout.setAlignment(FlowLayout.CENTER);
btnPanel = new JPanel(btnLayout);
btnLogin = new JButton("确定");
btnCancel = new JButton("取消");
btnPanel.add(btnLogin);
btnPanel.add(btnCancel);
btnCancel.addActionListener(this);
btnLogin.addActionListener(this);
mainPanel.add(namePanel);
mainPanel.add(btnPanel);
setContentPane(mainPanel);
tfName.addFocusListener(this);
tfPsd.addFocusListener(this);
pack();
setSize(WIDTH, HEIGHT);
setLocationRelativeTo(null);
}
@Override
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if(source == btnCancel) {
System.exit(0);
} else if(source == btnLogin) {
String username = tfName.getText();
String password = tfPsd.getText();
boolean success = service.login(username, password);
if(success) {
warn("成功", "登录成功！");
} else {
warn("失败", "您输入的用户名或密码错误 ！");
}
}
}
@Override
public void focusGained(FocusEvent arg0) {
}
@Override
public void focusLost(FocusEvent e) {
Object source = e.getSource();
if(source == tfName) {
String username = tfName.getText();
try {
service.matchUsername(username);
} catch (LoginException e1) {
warn("验证错误", e1.getMessage());
}
} else if(source == tfPsd) {
String password = tfPsd.getText();
try {
service.matchPassword(password);
} catch (LoginException e1) {
warn("验证错误", e1.getMessage());
}
}
}
private void warn(String title, String msg) {
JOptionPane.showMessageDialog(null, msg, title, JOptionPane.INFORMATION_MESSAGE);
}
public static void main(String[] args) {
new LoinWindow().launch();
}
}
然后是模型层：LoginDao
public class LoginDao {
public boolean login(String username, String password) {
if(username.equals("admin") password.equals("12345")) {
return true;
}
return false;
}
}
LoginService
import java.util.regex.Pattern;
public class LoginService {
private static final Pattern LOGIN_PATTERN = Pattern.compile("[a-zA-Z]+");
private static final Pattern PASSWORD_PATTERN = Pattern.compile("[1-9]+");
private LoginDao dao = new LoginDao();
public boolean matchUsername(String username) throws LoginException {
if(null == username || username.isEmpty()) {
return false;
}
if(!LOGIN_PATTERN.matcher(username).matches()) {
throw new LoginException("您输入的用户名不合法，请输入英文！");
}
return true;
}
public boolean matchPassword(String password) throws LoginException {
if(null == password || password.isEmpty()) {
return false;
}
if(!PASSWORD_PATTERN.matcher(password).matches()) {
throw new LoginException("您输入的密码不合法，请输入数字！");
}
return true;
}
public boolean login(String username, String password) {
if(null == username || username.isEmpty()) {
return false;
}
if(null == password || password.isEmpty()) {
return false;
}
if(!dao.login(username, password)) {
return false;
}
return true;
}
}
LoginException
public class LoginException extends Exception {
public LoginException(String arg0) {
super(arg0);
}
}
不知道分层设计思想是不是我想的这样
Q4: 如何用java 或C语言代码怎么实现如下功能：
要在java中调用c语言的库,需要使用Java提供了JNI。
举例说明
在c语言中定义一个 void sayHello()函数(打印Hello World);然后在Java中调用这个函数显示Hello Word.
现在分别从Java和C语言两部分说明:
1. Java 部分
首先定义一个HelloNative,在其中申明sayHello函数,函数要申明为Native 类型的.如下:
public class HelloNative {
public native void sayHello();
}
编译这个类,生成class文件:
javac HelloWorld.java
利用javah生成需要的h文件
javah HelloNative
生成的 h文件大概如下:
/* DO NOT EDIT THIS FILE - it is machine generated */
#include jni.h
/* Header for class HelloNative */
#ifndef _Included_HelloNative
#define _Included_HelloNative
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class: HelloNative
* Method: sayHello
* Signature: ()V
*/
JNIEXPORT void JNICALL Java_HelloNative_sayHello
(JNIEnv *, jobject);
#ifdef __cplusplus
}
#endif
#endif
可以看一下上面自动生成的程序,程序include了jni.h,这个头文件在 $JAVA_HOME下的include文件夹下. 还可以发现生成的函数名是在之前的函数名前面加上了Java_HelloNative。
2. C语言部分
根据上面生成的h文件编写相应的代码实现,建立一个 HelloNative.cpp用来实现显示Hello World的函数.如下:
#include stdio.h
#include "HelloNative.h"
JNIEXPORT void JNICALL Java_HelloNative_sayHello(JNIEnv *, jobject)
{
printf("Hello World!\n");
}
代码编写完成之后,我们再用gcc编译成库文件,命令如下;
gcc -fPIC -I/usr/lib/jvm/java-7-openjdk-i386/include -I/usr/lib/jvm/java-7-openjdk-i386/include/linux -shared -o libHelloNative.so HelloNative.cpp
这样就会在当前目录下生成一个libHelloNative.so的库文件.这时需要的库已经生成,在C语言下的工作已经完成了.
接下来需要在Java中编写一个程序测试一下.在程序前,需要将我们的库载入进去.载入的方法是调用Java的 System.loadLibrary("HelloNative");
public class TestNative
{
static {
try {
System.loadLibrary("HelloNative");
}
catch(UnsatisfiedLinkError e) {
System.out.println( "Cannot load hello library:\n " + e.toString() );
}
}
public static void main(String[] args) {
HelloNative test = new HelloNative();
test.sayHello();
}
}
但是再编译后,运行的时候,问题又出现了.
Cannot load hello library:
java.lang.UnsatisfiedLinkError: no HelloNative in java.library.path
Exception in thread "main" java.lang.UnsatisfiedLinkError: HelloNative.sayHello()V
at HelloNative.sayHello(Native Method)
at TestNative.main(TestNative.java:13)
载入库失败,但是库明明就是放在当前文件夹下的,怎么会载入失败呢?
用System.getProperty("java.library.path")查看,发现java.library.path中并不u存在当前的目录.主要有以下的几个解决办法:
1) 将生成的库复制到java.library.path有的路径中去,当然这样不是很好
2) 设置环境变量export LD_LIBRARY_PATH=.:$LD_LIBRARY_PATH ,将当前的目录加入到LD_LIBRARY_PATH中
3) 设置java 的选项,将当前的目录加入到其中 .java -Djava.library.path=. $LD_LIBRARY_PATH
这样之后程序就能够成功的运行了.可以看见显示的"Hello World!"了
Q5: 怎么用java代码实现将文本框输入的内容按照设计的排版格式
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriter;
import javax.imageio.stream.ImageOutputStream;
public class Ttex {
BufferedImage bi = new BufferedImage(300, 200, BufferedImage.TYPE_INT_RGB);
public Ttex(String text) {
Graphics gr = bi.createGraphics();
gr.setColor(Color.white);
gr.fillRect(0, 0, bi.getWidth(), bi.getHeight());
gr.setColor(Color.GRAY);
gr.drawString(text, 10, 10);
}
/**
* 根据地址来保存文件
*
* @param dir
* 文件地址
*/
private void Save(String dir) {
BufferedImage image = bi;
// 得到系统支持的图片写入器
Iterator it = ImageIO.getImageWritersBySuffix("jpg");
ImageWriter iw = null;
if (it.hasNext()) {
try {
ImageOutputStream imgOut = ImageIO
.createImageOutputStream(new File(dir));
iw = (ImageWriter) it.next();
iw.setOutput(imgOut);
IIOImage iioi = new IIOImage(image, null, null);
iw.write(iioi);
imgOut.close();
iw.dispose();
} catch (IOException e1) {
}
}
}
public static void main(String[] args) {
Ttex m = new Ttex("0123456789");
m.Save("D:/1.jpg");
}
}
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