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本文链接:https://blog.csdn.net/weixin_42528266/article/details/102967023
char charAt(int index)
返回字符串中第index个字符。boolean equals(String other)
如果字符串与other相等,返回trueboolean equalsIgnoreCase(String other)
如果字符串与other相等(忽略大小写),则返回trueint length()
返回字符串的长度。String replace(char oldChar,char newChar)
返回一个新串,它是通过用 newChar 替换此字符串中出现的所有oldChar而生成的boolean startsWith(String prefix)
如果字符串以prefix开始,则返回trueboolean endsWith(String prefix)
如果字符串以prefix结尾,则返回trueString substring(int beginIndex)
String substring(int beginIndex,int endIndex)
返回一个新字符串,该串包含从原始字符串beginIndex到串尾或endIndex-1的所有字符String toLowerCase()
返回一个新字符串,该串将原始字符串中的所有大写字母改成小写字母String toUpperCase()
返回一个新字符串,该串将原始字符串中的所有小写字母改成大写字母String trim()
返回一个新字符串,该串删除了原始字符串头部和尾部的空格StringBuffer和StringBuilder非常类似,均代表可变的字符序列,而且方法也一样
代码示例
package com.cwl.base.day04.string;
/**
* @program: java_base
* @description:
* @author: ChenWenLong
* @create: 2019-11-07 20:02
**/
public class TestStringBuilder {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder(); //字符数组长度初始为16
StringBuilder sb1 = new StringBuilder(32); //字符数组长度初始为32
StringBuilder sb2 = new StringBuilder("abcd"); //字符数组长度初始为32, value[]={'a','b','c','d',\u0000,\u0000...}
sb2.append("efg");
sb2.append(true).append(321).append("随便"); //通过return this实现方法链.
System.out.println(sb2);
System.out.println("##################");
StringBuilder gh = new StringBuilder("a");
for (int i = 0; i < 1000; i++) {
gh.append(i);
}
System.out.println(gh);
StringBuilder sb4 = new StringBuilder("abcdefghijklmnopqrstuvwxyz");
sb.delete(3, 5).delete(3, 5); //结果:abchijklmnopqrstuvwxyz
System.out.println(sb);
sb.reverse();
System.out.println(sb);
StringBuffer sb3 = new StringBuffer();
}
}
string s="a"; //创建了一个字符串
s=s+"b"; //实际上原来的"a"字符串对象已经丢弃了,现在又产生了一个字符串s+"b"。
//如果多次执 行这些改变串内容的操作,会导致大量副本字符串对象存留在内存中,降低效率。
//如果这样的 操作放到循环中,会极大影响程序的性能。
代码示例
package com.cwl.base.day04.date;
import java.util.Date;
/**
* @program: java_base
* @description:
* @author: ChenWenLong
* @create: 2019-11-08 10:43
**/
public class TestDate {
public static void main(String[] args) {
Date d = new Date();
long t = System.currentTimeMillis();
System.out.println(t);
Date d2 = new Date(1000);
System.out.println(d2.toGMTString()); //不建议使用
d2.setTime(24324324);
System.out.println(d2.getTime());
System.out.println(d.getTime()<d2.getTime());
}
}
代码示例
package com.cwl.base.day04.date;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
* @program: java_base
* @description:
* @author: ChenWenLong
* @create: 2019-11-08 10:43
**/
public class TestDateFormat {
public static void main(String[] args) {
DateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss,属于本月的第W周");
Date d = new Date(12321314323L);
String str = df.format(d); //将时间对象按照格式化字符串,转化成字符串
System.out.println(str);
System.out.println("####################");
String str2 = "1977-7-7";
DateFormat df2 = new SimpleDateFormat("yyyy-MM-dd");
try {
Date d2 = df2.parse(str2);
System.out.println(d2);
} catch (ParseException e) {
e.printStackTrace();
}
}
}
代码示例
package com.cwl.base.day04.date;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
/**
* @program: java_base
* @description:
* @author: ChenWenLong
* @create: 2019-11-08 10:43
**/
public class TestCalendar {
public static void main(String[] args) {
Calendar c = new GregorianCalendar();
c.set(2001, Calendar.FEBRUARY, 10, 12, 23, 34);
// c.set(Calendar.YEAR, 2001);
// c.set(Calendar.MONTH, 1); //二月
// c.set(Calendar.DATE, 10);
// c.setTime(new Date());
Date d = c.getTime();
System.out.println(d);
System.out.println(c.get(Calendar.YEAR));
//测试日期计算
c.add(Calendar.MONTH, -30);
System.out.println(c);
}
}
package com.cwl.base.day04.date;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Scanner;
/**
* @program: java_base
* @description:
* @author: ChenWenLong
* @create: 2019-11-08 10:44
**/
public class VisualCalendar {
public static void main(String[] args) {
System.out.println("请输入日期(按照格式:2030-3-10):");
Scanner scanner = new Scanner(System.in);
String temp = scanner.nextLine();
DateFormat format = new SimpleDateFormat("yyyy-MM-dd");
try {
Date date = format.parse(temp);
Calendar calendar = new GregorianCalendar();
calendar.setTime(date);
int day = calendar.get(Calendar.DATE);
calendar.set(Calendar.DATE, 1);
int maxDate = calendar.getActualMaximum(Calendar.DATE);
System.out.println("日\t一\t二\t三\t四\t五\t六");
for(int i=1;i<calendar.get(Calendar.DAY_OF_WEEK);i++){
System.out.print('\t');
}
for(int i=1;i<=maxDate;i++){
if(i==day){
System.out.print("*");
}
System.out.print(i+"\t");
int w = calendar.get(Calendar.DAY_OF_WEEK);
if(w==Calendar.SATURDAY){
System.out.print('\n');
}
calendar.add(Calendar.DATE, 1);
}
} catch (ParseException e) {
e.printStackTrace();
}
}
}