一、正则表达式
1、正则表达式定义
2.常用正则表达式符号
3.用法示例1
import java.util.regex.Matcher
import java.util.regex.Pattern
import java.util.Scanner
public class test8 {
public static void main(String [] args) {
System.out.println("-------------------------------")
Pattern p = Pattern.compile("\\d{6}")
Matcher m = p.matcher("123456")
System.out.println(m.matches())
System.out.println("邮政编码验证"+m.matches())
System.out.println("-------------------------------")
p = Pattern.compile("1\\d{10}")
m = p.matcher("12345678902")
System.out.println("手机号验证"+m.matches())
System.out.println("-------------------------------")
Pattern pa = Pattern.compile("[a-zA-Z0-9]{4,10}")
Matcher ma = pa.matcher("sgg123")
System.out.println("用户名验证"+ma.matches())
ma = pa.matcher("234")
System.out.println("用户名验证"+ma.matches())
}
}
4.用法示例2:
/**
* 正则表达式
*/
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class test7 {
public static void main(String[] args) {
Pattern p = Pattern.compile("\\d{6}");
Matcher m = p.matcher("123456");
System.out.println(m.matches());
}
}
二、局部代码块:
用大括号括起来,限制局部变量的使用范围和生命周期。
public void 方法中 {
{
作用:限制局部变量的使用范围和销毁范围
}
}
静态导入
package a1;
public class A1 {
public void sf1() {
System.out.println("helloword");
}
}
--------------------------------------------------------------------
package b1;
import static a1.A1.sf1;
import statica1.A1.*;
public class B1 {
public void show () {
sf1();
System.out.println();
}
}
三、单例模式
只能创建一个对象的类。
(一)实现方式一(饿汉式实现方式)
class Window {
private static Window win = new Window();
private Window(){
}
public Window getInstance () {
return win;
}
}
public class TestWindow {
public static void main(String[]args) {
Window win1 = Window.getInstance();
Window win2 = Window.getInstance();
System.out.println(win1);
System.out.println(win2);
}
}
(二)实现方式二(懒汉式实现方式)
class Window {
private static Window win = null;
private Window(){
}
public Window getInstance () {
if(win == null) {
win = new Window();
}
return win;
}
}
public class TestWindow {
public static void main(String[]args) {
Window win1 = Window.getInstance();
Window win2 = Window.getInstance();
System.out.println(win1);
System.out.println(win2);
}
}
懒汉式和饿汉式区别:
- 1.饿汉式 静态变量在类加载时已经创建对象了;而懒汉式只有在调用方法时才创建对象赋值;
- 2.多线程情况下饿汉式相对安全;