1、字符串相关的类
String类
String常用的方法
常用方法测试
package com.lcy;
public class StringTest {
public static void main(String[] args) {
String str = "12hello34world5java7891mysql456";
//把字符串中的数字替换成,,如果结果中开头和结尾有,的话去掉
String string = str.replaceAll("\\d+", ",").replaceAll("^,|,$", "");
System.out.println(string);
System.out.println("----------------------------");
String str1 = "12345";
//判断str字符串中是否全部有数字组成,即有1 - n个数字组成
boolean matches = str1.matches("\\d+");
System.out.println(matches);
System.out.println("----------------------------");
String tel = "0571-4534289";
//判断这是否是一个杭州的固定电话
boolean result = tel.matches("0571-\\d{7,8}");
System.out.println(result);
System.out.println("----------------------------");
String str2 = "hello|world|java";
String[] strs = str2.split("\\|");
for (int i = 0; i < strs.length; i++) {
System.out.println(strs[i]);
}
System.out.println("----------------------------");
String str3 = "hello.world.java";
String[] strs2 = str3.split("\\.");
for (int i = 0; i < strs2.length; i++) {
System.out.println(strs2[i]);
}
}
}
测试结果:
StringBuffer类
StringBuilder类
2、日期时间API
package com.lcy;
import java.util.Date;
public class StringBuffer {
public static void main(String[] args) {
Date date = new Date();
System.out.println(date); //Wed Jan 29 12:35:40 CST 2020
System.out.println(System.currentTimeMillis()); //1580272540654
System.out.println(date.getTime()); //1580272540637
Date date1 = new Date(date.getTime());
System.out.println(date1.getTime()); //1580272540637
System.out.println(date1.toString()); //Wed Jan 29 12:35:40 CST 2020
}
}
package com.lcy;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Data {
public static void main(String[] args) {
Date date = new Date();
SimpleDateFormat formater = new SimpleDateFormat();
System.out.println(formater.format(date)); //20-1-29 下午5:50
SimpleDateFormat formater2 = new SimpleDateFormat("yyyy年MM月dd日EEE HH:mm:ss");
System.out.println(formater2.format(date));//2020年01月29日星期三 17:50:42
}
}
package com.lcy;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class Data {
public static void main(String[] args) {
System.out.println("-------------");
Calendar calendar = Calendar.getInstance();
// 从一个Calendar 对象中获取Date对象
Date date = calendar.getTime();
// 使用给定的Date 设置此Calendar 的时间
date = new Date(234234235235L);
calendar.setTime(date);
calendar.set(Calendar.DAY_OF_MONTH, 8);
System.out.println("当前时间日设置为8后,时间是:" + calendar.getTime());
calendar.add(Calendar.HOUR, 2);
System.out.println("当前时间加2小时后,时间是:" + calendar.getTime());
calendar.add(Calendar.MONTH, -2);
System.out.println("当前日期减2个月后,时间是:" + calendar.getTime());
}
}
3、 Java比较器
4、System类
5 Math类
6 BigInteger与BigDecimal
package com.lcy;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
public class Data {
public static void main(String[] args) {
BigInteger bi = new BigInteger("12433241123");
BigDecimal bd = new BigDecimal("12435.351");
BigDecimal bd2 = new BigDecimal("11");
System.out.println(bi);
// System.out.println(bd.divide(bd2));
System.out.println(bd.divide(bd2, BigDecimal.ROUND_HALF_UP));
System.out.println(bd.divide(bd2, 15, BigDecimal.ROUND_HALF_UP));
}
}