前言
本期任务：毕向东老师Java视频教程学习笔记（共计25天）
原视频链接：黑马程序员_毕向东_Java基础视频教程day01：编写HelloWorld程序day02：操作符与条件选择语句day03：循环语句与函数day04：数组day07：继承、抽象类与接口day08：多态day09：异常处理day11：多线程day12：线程安全与同步机制day13：String类day14：集合（ArrayList，LinkedList，HashSet）day15：集合（TreeSet）和泛型）day16：集合（HashMap、TreeMap）day17：集合框架的工具类（Arrays、Collections）day18：IO流（字符流读写）day19：IO流（字节流、转换流读写）day20：IO流（File对象）
代码
import java
.io
.*
;
public class FileWriterDemo {
public static void main(String
[] args
) throws Exception
{
FileWriter fw
= new FileWriter("demo.txt");
fw
.write("fsgd");
fw
.close();
}
}
import java
.io
.*
;
public class FileWriterDemo2 {
public static void main(String
[] args
) {
FileWriter fw
= null
;
try {
fw
= new FileWriter("demo.txt");
fw
.write("dfalkjf;");
} catch (IOException e
) {
System
.out
.println("catch: " + e
.toString());
} finally {
try {
if (fw
!= null
)
fw
.close();
} catch (IOException e
) {
System
.out
.println(e
.toString());
}
}
}
}
import java
.io
.*
;
public class FileWriterDemo3 {
public static void main(String
[] args
) throws IOException
{
FileWriter fw
= new FileWriter("demo.txt", true);
fw
.write("\r\n这是续写的部分内容。。。。\r\n");
fw
.close();
}
}
import java
.io
.FileReader
;
import java
.io
.IOException
;
public class FileReaderDemo {
public static void main(String
[] args
)throws IOException
{
FileReader fr
= new FileReader("demo.txt");
int ch
= 0;
while ((ch
=fr
.read())!=-1){
System
.out
.println((char)ch
);
}
fr
.close();
}
}
import java
.io
.FileReader
;
import java
.io
.IOException
;
public class FileReaderDemo2 {
public static void main(String
[] args
) throws IOException
{
FileReader fr
= new FileReader("demo.txt");
char[] buf
= new char[1024];
int num
= 0;
while ((num
= fr
.read(buf
)) != -1) {
System
.out
.println(new String(buf
, 0, num
));
}
fr
.close();
}
}
import java
.io
.*
;
public class CopyText {
public static void main(String
[] args
) throws Exception
{
FileReader fr
= new FileReader("demo.txt");
FileWriter fw
= new FileWriter("demo_copy.txt");
char[] buf
= new char[1024];
int num
= 0;
while ((num
=fr
.read(buf
))!=-1){
fw
.write(buf
, 0, num
);
}
fr
.close();
fw
.close();
}
}
import java
.util
.*
;
import java
.text
.*
;
public class DateDemo {
public static void main(String
[] args
) {
Date d
= new Date();
System
.out
.println(d
);
SimpleDateFormat sdf
= new SimpleDateFormat("yyyy年MM月dd日 E kk:mm:ss");
System
.out
.println("time: "+sdf
.format(d
));
long l
= System
.currentTimeMillis();
System
.out
.println(new Date(l
));
}
}
import java
.util
.*
;
import java
.text
.*
;
public class CalendarDemo {
public static void main(String
[] args
) {
Calendar c
= Calendar
.getInstance();
System
.out
.println(c
);
String
[] mons
= {"1月", "2月", "3月", "4月", "5月", "6月", "7月", "8月", "9月", "10月", "11月", "12月"};
String
[] weeks
= {"星期一", "星期二", "星期三", "星期四", "星期五", "星期六", "星期日"};
int year
= c
.get(Calendar
.YEAR
);
int month
= c
.get(Calendar
.MONTH
);
int day
= c
.get(Calendar
.DAY_OF_MONTH
);
int week
= c
.get(Calendar
.DAY_OF_WEEK
);
System
.out
.println(year
+ "年" + mons
[month
] + day
+ "日" + weeks
[week
]);
}
}
import java
.util
.*
;
public class CalendarDemo2 {
public static void main(String
[] args
) {
curTimeYesterday();
}
public static int howManyDaysInFebruary(int year
) {
Calendar c
= Calendar
.getInstance();
c
.set(year
, 2, 1);
c
.add(Calendar
.DAY_OF_MONTH
, -1);
return c
.get(Calendar
.DAY_OF_MONTH
);
}
public static void curTimeYesterday() {
Calendar c
= Calendar
.getInstance();
c
.add(Calendar
.DAY_OF_MONTH
, -1);
int year
= c
.get(Calendar
.YEAR
);
int month
= c
.get(Calendar
.MONTH
)+1;
int day
= c
.get(Calendar
.DAY_OF_MONTH
);
int hour
= c
.get(Calendar
.HOUR
);
int min
= c
.get(Calendar
.MINUTE
);
int sec
= c
.get(Calendar
.SECOND
);
System
.out
.println("昨天的这个时候是：" + year
+ "年" + month
+ "月" + day
+ "日" + hour
+ "时" + min
+ "分" + sec
+ "秒");
}
}
import java
.util
.*
;
public class MathDemo {
public static void main(String
[] args
) {
saveTwo(12.3456, 2, true);
}
public static void saveTwo(double d
, int scale
, boolean isRound
) {
double base
= Math
.pow(10, scale
);
double num
= isRound
? Math
.round(d
* base
) / base
: (int) (d
* base
) / base
;
System
.out
.println("num = " + num
);
}
public static void show() {
System
.out
.println(Math
.ceil(16.34));
System
.out
.println(Math
.floor(12.34));
System
.out
.println(Math
.round(12.34));
System
.out
.println(Math
.pow(2, 3));
System
.out
.println("..................................");
Random r
= new Random();
for (int x
= 0; x
< 10; x
++) {
System
.out
.println(r
.nextInt(10) + 1);
}
}
}
import java
.util
.*
;
public class SystemDemo {
public static void main(String
[] args
) {
Properties prop
= System
.getProperties();
for (Object obj
: prop
.keySet()){
System
.out
.println(obj
+"::"+prop
.get(obj
));
}
System
.setProperty("myKey", "myValue");
System
.out
.println("os.name: "+ System
.getProperty("os.name"));
System
.out
.println("myKey: "+ System
.getProperty("myKey"));
}
}
public class RuntimeDemo {
public static void main(String
[] args
) throws Exception
{
Runtime r
= Runtime
.getRuntime();
Process p
= r
.exec("notepad.exe RuntimeDemo.java");
Thread
.sleep(4000);
p
.destroy();
}
}
