java.text
类 Format

直接已知子类： DateFormat, MessageFormat, NumberFormat
Format 是一个用于格式化语言环境敏感的信息（如日期、消息和数字）的抽象基类。
Format 定义了编程接口，用于将语言环境敏感的对象格式化为 String（使用 format 方法）和将 String 重新解析为对象（使用 parseObject 方法）。
通常，一个 format 的 parseObject 方法必须能解析任何由其 format 方法格式化的字符串。不过，也可能存在不能解析的异常情况。例如， format 方法可能创建中间无分隔符的两个相邻整数，在这种情况下， parseObject 无法判断哪个数字属于哪个数。
SimpleDateFormat 是一个以与语言环境有关的方式来格式化和解析日期的具体类。它允许进行格式化（日期 -> 文本）、解析（文本 -> 日期）和规范化。

/**
         * 把符合日期格式的字符串转换为日期类型
         */
         public static java.util.Date stringtoDate(String dateStr, String format) {
                Date d = null;
                SimpleDateFormat formater = new SimpleDateFormat(format);
                 try {
                        formater.setLenient( false);
                        d = formater.parse(dateStr);
                } catch (Exception e) {
                         // log.error(e);
                        d = null;
                }
                 return d;
        }

/**
         * 把日期转换为字符串
         */
         public static String dateToString(java.util.Date date, String format) {
                String result = "";
                SimpleDateFormat formater = new SimpleDateFormat(format);
                 try {
                        result = formater.format(date);
                } catch (Exception e) {
                         // log.error(e);
                }
                 return result;
        }
/**
         * 获得某月的天数
         */
         public static int getDaysOfMonth(String year, String month) {
                 int days = 0;
                 if (month.equals( "1") || month.equals( "3") || month.equals( "5")
                                || month.equals( "7") || month.equals( "8") || month.equals( "10")
                                || month.equals( "12")) {
                        days = 31;
                } else if (month.equals( "4") || month.equals( "6") || month.equals( "9")
                                || month.equals( "11")) {
                        days = 30;
                } else {
                         if ((Integer.parseInt(year) % 4 == 0 && Integer.parseInt(year) % 100 != 0)
                                        || Integer.parseInt(year) % 400 == 0) {
                                days = 29;
                        } else {
                                days = 28;
                        }
                }

                 return days;
        }

2） java dos输入输出
import java.util.Scanner;

public class DaoXu {

   public static void main(String[] args) {
     // TODO 自动生成方法存根
    System.out.println( "请输入单个字符并回车: ");
    Scanner c = new Scanner(System.in);

    String[] ch = new String[5];

     for ( int i = 0; i < 5; i++) {
      ch[i] = c.next();
    }
     // Arrays.sort(ch);
    System.out.print( "倒序输出: ");
     for ( int j = ch.length - 1; j >= 0; j--) {
      System.out.print(ch[j] + " ");
    }
  }
}
3） java获取ip地址

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.InetAddress;
import java.net.UnknownHostException;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class IP extends JFrame implements ActionListener {
   private static final long serialVersionUID = 3339481369781127417L;
  JButton jb1;
  JButton jb2;
  JButton jb3;
  JPanel jp;
  JLabel jl;
  JLabel jl1;
  JTextField jt;

   public IP() {
     this.jp = new JPanel();
     this.jl = new JLabel();
     this.jl1 = new JLabel( "您的域名：");
     this.jb1 = new JButton( "提交");
     this.jb2 = new JButton( "重置");
     this.jb3 = new JButton( "退出");
     this.jt = new JTextField(20);
     this.jb1.addActionListener( this);
     this.jb2.addActionListener( this);
     this.jb3.addActionListener( this);
     this.jp.setLayout( new GridLayout(3, 2));
     this.jp.add( this.jl1);
     this.jp.add( this.jt);
     this.jp.add( this.jb1);
     this.jp.add( this.jl);
     this.jp.add( this.jb2);
     this.jp.add( this.jb3);

    setBounds(200, 200, 500, 240);
    add( this.jp);
    setVisible( true);
    setDefaultCloseOperation(3);
  }

   public static void main(String[] args) {
     new IP();
  }

   public void actionPerformed(ActionEvent e) {
     if (e.getSource() == this.jb1) {
      String url = this.jt.getText();
      InetAddress ip = null;
       try {
        ip = InetAddress.getByName(url);
      } catch (UnknownHostException e1) {
        e1.printStackTrace();
      }
       this.jl.setText(ip.toString());
    } else if (e.getSource() == this.jb2) {
       this.jl.setText("");
       this.jt.setText("");
    } else {
      System.exit(0);
    }
  }
}