public class TestDecimalFormat {
public static void main(String[] args) {
/*
* #:代表数字
* 0:代表不够补零
* .:代表小数位
* ,:代表千分位
* */
DecimalFormat df=new DecimalFormat("##,###,###.##");
String format = df.format(1231231.2351231);
System.out.println(format);
df=new DecimalFormat("##.00000");
String format1 = df.format(123.1);
System.out.println(format1);
}
}
public class TestBigDecimal {
public static void main(String[] args) {
BigDecimal a=new BigDecimal("1231230000");
BigDecimal b=new BigDecimal("123123");
//加
BigDecimal add = a.add(b);
System.out.println(add);
//减
BigDecimal subtract = a.subtract(b);
System.out.println(subtract);
//乘
BigDecimal multiply = a.multiply(b);
System.out.println(multiply);
//除(除不尽会报错)
BigDecimal divide = a.divide(b);
System.out.println(divide);
}
}
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-pfQW3OBO-1593848759427)(upload/image-20200702163031785.png)]
public class TestRandom {
public static void main(String[] args) {
Random random = new Random();
//获取[0,11)之间的整数
int i = random.nextInt(11);
System.out.println(i);
}
}
package com.xd.api;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class TestDate {
public static void main(String[] args) throws ParseException {
//获取系统当前时间
Date date=new Date();
System.out.println("1、获取系统当前时间:"+date);
//格式化输出
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss (a)(EE)");
String format = sdf.format(date);
System.out.println("2、格式化后的输出:"+format);
//字符串转时间
String time = "2020-10-10 08:08:07";
SimpleDateFormat sdf2=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date parse = sdf2.parse(time);
String format1 = sdf.format(parse);
System.out.println("3、字符串转时间后的格式"+format1);
//获取时间戳
long l = System.currentTimeMillis();
System.out.println("4、获取当前时间的时间戳:"+new Date(l));
//获取昨天现在的时间
l=l-1000*60*60*24;
System.out.println("5、获取昨天现在的时间:"+new Date(l));
}
}
package com.xd.api;
import java.util.Calendar;
import java.util.Date;
public class TestCalender {
public static void main(String[] args) {
Calendar calendar=Calendar.getInstance();
calendar.setTime(new Date());
String year=String.valueOf(calendar.get(Calendar.YEAR));
String month=String.valueOf(calendar.get(Calendar.MONTH)+1);//因为月份少一
String day=String.valueOf(calendar.get(Calendar.DATE));
String week=String.valueOf(calendar.get(Calendar.DAY_OF_WEEK)-1);//国外星期日为第一天
System.out.println("1、今天是:"+year+"-"+month+"-"+day+" 星期:"+week);
int hour=calendar.get(Calendar.HOUR);
int minute=calendar.get(Calendar.MINUTE);
int second=calendar.get(Calendar.SECOND);
System.out.println("2、时间:"+hour+":"+minute+":"+second);
//计算两个时间相隔多少天
calendar.set(2020,5,5);
long timeInMillis = calendar.getTimeInMillis();
calendar.set(2020,7,3);
long timeInMillis1 = calendar.getTimeInMillis();
long days=Math.abs(timeInMillis1-timeInMillis)/(24*60*60*1000);
System.out.println("3、相隔:"+days+"天");
}
}
https://www.runoob.com/java/java-regular-expressions.html 正则语法
分隔需要转义的字符:
| \ $ * + . ? ^ ( ) [ ] { }
package com.xd.api;
import java.util.Arrays;
public class TestString {
public static void main(String[] args) {
String str=new String("I love Java");
//转化为数组
char[] chars = str.toCharArray();
System.out.println("1、字符串转化为字符数组:"+ Arrays.toString(chars));
String s = String.valueOf(chars);
System.out.println("2、数组转化为字符串:"+s);
//获取索引上的字符,获取J
char j = str.charAt(str.indexOf("J"));
System.out.println("3、获取J:"+j);
//最后一次的索引值
System.out.println("4、最后一次的索引值:"+str.lastIndexOf("a"));
//后缀
System.out.println(str.endsWith("ava"));
//前缀 重载的有个偏移量toffset
System.out.println(str.startsWith("a"));
//正则匹配正则符号需要用()括起来
System.out.println("5、正则匹配"+str.matches("(.*)ava"));
//替换 ==注意常量池==replace会改变原来的String
String replaceStr=new String(str);
replaceStr.replace("L", "l");
System.out.println("6、替换前:"+str);
System.out.println("7、替换后:"+replaceStr);
//比较两个值是否相等
String str2="i love Java";
System.out.println(str.equals(str2));
System.out.println(str.equalsIgnoreCase(str2));
//切割
System.out.println("8、切割后的:"+str.substring(5));
//转大小写
String s1 = str.toLowerCase();
System.out.println("9、小写:"+s1);
String s2 = str.toUpperCase();
System.out.println("10、大写:"+s2);
StringBuilder sb=new StringBuilder(str);
sb.reverse();
System.out.println("11、字符串反转:"+sb);
StringBuffer sb2=new StringBuffer(str);
System.out.println("12、字符串反转:"+sb2.reverse());
//字符串的分隔
System.out.println("13、分隔:当前字符串:"+str);
String[] s3 = str.split(" ");
System.out.println("14、分隔后的字符串:"+Arrays.toString(s3));
String test="[email protected]";
String[] split = test.split("\\.");
System.out.println("15、分隔后的字符串:"+Arrays.toString(split));
//删除字符串的前后空格
String str3 =" xd ";
System.out.println("16、开始长度:"+str3.length());
System.out.println(str3.trim()+"删除空格后的长度:"+str3.trim().length());
}
}
//追加、反转
//追加、反转
https://www.runoob.com/java/java-regular-expressions.html
/**
^ 开头
$ 结尾
. 任意字符
? 没有或者一个
* 没有或者多个
+ 一个或者多个
[abc] 匹配a或b或c
{a,b} 匹配a个到b个
**/
public class TestMath {
public static void main(String[] args) {
int a=10;
int b=2;
int c=-2;
//求a的平方
double sqrt = Math.sqrt(a);
System.out.println("a的平方"+a);
//三个数比较最大值
int max = Math.max(a, b);
int max1 = Math.max(max, c);
System.out.println("最大值:"+max1);
//次方
double pow = Math.pow(b, a);
System.out.println("2的10次方:"+pow);
for (int i = 0; i < 20; i++) {
//产生[0.0,1.0)之间的数
System.out.println(Math.random());
}
}
}
public class TestSystem {
public static void main(String[] args) {
//获取当前时间的毫秒戳
long l = System.currentTimeMillis();
char[] a=new char[]{'1','3','3','4'};
//从a数组下标为1开始克隆,放到a数组下标为3的地方,放置1个
System.arraycopy(a,1,a,3,1);
System.out.println(Arrays.toString(a));
}
}
public class TestArrays {
public static void main(String[] args) {
int[] a=new int[]{1,2,3,2,2,3,4,5,6,7,6,5,4};
//排序
Arrays.sort(a);
System.out.println(Arrays.toString(a));
//二分法查找
int i = Arrays.binarySearch(a, 7);
//是排序后的下标
System.out.println("7的位置:"+i);
}
}
public class 相互转化 {
public static void main(String[] args) {
String strNum="123";
int intNum=123;
Integer integer=123;
//引用数据类型与基本数据类型。true 自动拆箱装箱
System.out.println(integer.equals(intNum));
//String转int
int i = Integer.parseInt(strNum);
//String转Integer
Integer integer1 = Integer.valueOf(strNum);
//int转String
String s = String.valueOf(intNum);
//Integer转String
String s1 = String.valueOf(integer);
//Integer转int
int i1 = integer.intValue();
}
}
public class TestStringTokenizer {
public static void main(String[] args) {
String ip="192.168.1.0";
StringTokenizer st=new StringTokenizer(ip,"\\.");
int num=st.countTokens();
while(st.hasMoreTokens()){
System.out.println(st.nextToken());
}
}
}