Jave基础3

package Number;
import java.util.Date;//导入类
public class First {
	static String s1 = "Hello";//静态全局变量（可以跨类）
	public static void main(String [] args) {
//字符串
		//String && new String构建
		String str1="hello";
		String str2=new String("world");
		String str=str1+" "+str2;//通过“+”连接
		System.out.println(str);
		int booktime=4;
		float practice=2.5f;
		System.out.println("我每天花费"+booktime+"小时看书，"+practice+"小时听歌；");
//获取字符串信息
		//1.长度str.length()
		int size=str1.length();
		System.out.println(size);
		//2.查找indexOf(String s)=>返回首次位置 && lastIndexOf(String s)=>返回末次位置
		int a=str1.indexOf("l");
		int b=str1.lastIndexOf("l");
		System.out.println(a+" "+b);
		//3.获取指定索引位置的字符str.charAt(int index)
		char c=str2.charAt(2);
		System.out.println(c);
//字符串操作
		//1.获取子字符串str.substring(int beginIndex) && substring(int beginIndex,int endIndex)=>截取
		String str3=str2.substring(3);
		System.out.println(str3);
		//2.去除空格str.trim()=>忽略前导和尾部的空格
		str="123 222 2";
		System.out.println(str);
		System.out.println("原来的长度："+str.length());
		System.out.println("去除空格的长度："+str.trim().length());
		str=" 123 222 2 ";
		System.out.println(str);
		System.out.println("原来的长度："+str.length());
		System.out.println("去除空格的长度："+str.trim().length());
		//3.字符串替换str.replace(char oldChar,char newChar)=>更换其中的字符或字符串
		String newstr=str.replace("2","a");
		System.out.println(newstr);
		//4.判断字符串开头和结尾str.startsWith(String prefix) && str.endsWith(String suffix)
		String n1="221351";
		String n2="3261351";
		boolean b1=n1.startsWith("22");//是否“22”开头
		boolean b2=n2.endsWith("352");//是否“351”结尾
		System.out.println(b1);
		System.out.println(b2);
		//5.判断是否相等str.equals(String otherstr) && str.equalsIgnoreCase(String otherstr)
		str1="ABC";
		str2="abc";
		b1=str1.equals(str2);//区分大小写
		b2=str1.equalsIgnoreCase(str2);//不区分大小写
		System.out.println(b1+" "+b2);
		//6.按字典顺序比较两个字符串str.compareTo(String otherstr)
		//str在otherstr后为1，前为-1，等为0
		str1="a";
		str2="b";
		str3="c";
		str="b";
		System.out.println(str.compareTo(str1)+" "+str.compareTo(str2)+" "+str.compareTo(str3));
		//7.大小写转换str.toLowerCase()=>小写 && str.toUpperCase()=>大写
		System.out.println(str1.toUpperCase()+str2.toLowerCase());
		//8.字符串切割str.split(String sign) && str.split(String sign,int limit)//分割次数
		str="192.168.0.1";
		String[] first=str.split("\\.");
		String[] secend=str.split("\\.",2);
		System.out.println(str);
		for(String k:first) {//遍历
			System.out.print("["+k+"]");
		}
		System.out.println();
		for(String l:secend) {
			System.out.print("["+l+"]");
		}
		System.out.println();
//格式化字符串String.format()
		Date date = new Date();
		String year=String.format("%tY", date);
		String month=String.format("%tB",date);
		String day=String.format("%td", date);
		System.out.println(year+"/"+month+"/"+day);
//正则表达式用于检查是否满足某一格式str.matches(regex)
		String regex="\\w+@+\\w+(\\.\\w{2,3})*\\.\\w{2,3}";
		str1="aaa@";
		str2="sssss";
		str3="11@11fd.dfg.com";
		if(str1.matches(regex)) {
			System.out.println(str1+"合法Email");
		}
		if(str2.matches(regex)) {
			System.out.println(str2+"合法Email");
		}
		if(str3.matches(regex)) {
			System.out.println(str3+"合法Email");
		}
		
		
		
		
		
	}
}