Franic_ wy 2022-01-26 13:51:13 阅读数:909
1.Java The file name suffix is . java
2. When saving, the file name must be consistent with the class name ,Java The basic unit of a program ： class (class)
3. stay Java There are the following ways of annotation in ：
Block annotation ：/* */ Line notes ：// （ and C The way of annotation in language is the same ）
Javadoc notes ：
/**
* @author
* @param
*/
4. Program entry ： The main function ：main（）
5. stay Windows in java How the program compiles ：
First, make sure that the file name and class name are consistent ： javac Hello.java ---> Hello.class
6. stay Windows in java How the program works ：
java Hello[.class] ---> function Hello.class file
Be careful ： stay 5. 6. Need to know in the process Windows Terminal tool entry and usage .
## Terminal tools
win + R --> cmd
Basic instructions
cls ---> clear screen Clear the screen
dir ---> directory List the files in the current directory
cd ---> change directory Toggle directory
. Current directory （cd.）
.. Previous Directory （cd..）
Root switch ：C: D: E: F: （ Input the drive letter directly + The colon ： d: e:）
1. Build a writing environment
1. Notepad
2. recommend ：vscode
3. install ：https://code.visualstudio.com/
4. Add right click menu ： perform "VsCode Right-click menu .reg"
modify reg In file vscode Installation path for
2. Build a terminal enhancement environment
1.win+R -> cmd
2. recommend ：cmder
3. install ：https://cmder.net/
4. Add right click menu ：
1. Get into cmder The installation directory
2. Run as administrator cmder.exe
3. Enter... In the pop-up window
cmder.exe /register all 3. install JDK
JDK: Java Development Kit
JRE （JDK contain JRE）
JVM （JRE contain JVM）
JRE: Java Runtime Environment
JVM: Java Virtual Machine
1. download ：https://www.oracle.com/java/technologies/downloads/#java8-windows
2.java8->windows->x64
4. add to Java Related environment variables ( Optional )
newly build ：JAVA_HOME = C:\Program Files\Java\jdk1.8.0_151
newly build ：CLASSPATH = .
edit ：PATH = %JAVA_HOME%\bin
Computer -> Right click in the blank space -> Advanced system setup -> senior -> environment variable
User variables
System variables
5. Verify the correctness of the environment installation
use java -version
public class Hello{
/**
* can @
*/
public static void main(String[] args){
//Print Line（ Output line feed ） amount to C:\n
System.out.println("Hello World");
}
}project
class
package:
class1
class2
package:
class1
class2
The full name of a class ： Package name . Class name
com.zhongbei.Angle
constraint ：
1. The class name must be the same as the file name
2. The package name must match the file level / The structure is consistent
class: com.zhongbei.Angle
dir: com/zhongbei/Angle.java
How to compile / function
1. Compilation is not affected , Just find the corresponding file
2. function
java com.zhongbei.Angle
You must switch to the top-level directory of the package ：com At the same directory
package com.zhongbei;
public class Angle{
public static void main(String[] args){
System.out.println("This is main function.");
double res = sin(30);
System.out.println("sin(30) = " + res);
}
public static double sin(int angle){
double result = 0.0;
switch(angle){
case 30:
result = 0.5; break;
case 45:
result = 0.7; break;
case 60:
result = 0.8; break;
default:
break;
}
return result;
}
} 5、 ... and . The representation of numbers
0 1
Low level 0
High level 1
'a': ascii, 97
'b'
'c'
'd'
' chinese ' unicode
1.ASCII
'a' - 'z' 97 - 122 0x61 - 0x7A
'A' - 'Z' 65 - 90 0x41 - 0x5A
'0' - '9' 48 - 57 0x30 - 0x39
'\0' 0
"hello",'h','e','l','l','o','\0'
2. Base number
Decimal system 764
Binary system [0-1] b1101 0111
octal [0-7] 0764
Hexadecimal [0-9A-F] 0x764
Binary system --> Decimal system
b0000 0001 1
b0000 1111 15
b0000 1011 11
b0000 0111 7
Decimal system --> Binary system ( except 2 Remainder reverse order )
60/2 30 0
30/2 15 0
15/2 7 1
7/2 3 1
3/2 1 1
1/2 0 1
60 == b111100
octal -> Decimal system
0641 -> 6 * 8^2 + 4*8^1 + 1*8^0 = xxx
octal -> Binary system (1 individual 8 Base bit == 3 individual 2 Base bit )
0641 -> b110 100 001
Binary system -> octal
b010 110 110 -> 0266
Hexadecimal -> Decimal system
0xA38F = 10 * 16^3 + 3 * 16^2 + 8 *16^1 + 15 * 16^0
Hexadecimal -> Binary system (1 individual 16 Base bit == 4 individual 2 Base bit )
0xA38F = b1010 0011 1000 1111
Binary system -> Hexadecimal binary
b1001 1100 = 0x9C
Hexadecimal -> octal
3. Integer representation ( A signed 、 Unsigned )
1byte = 8bit
b1010 0111
unsigned:
b0000 0000 ~ b1111 1111 0 ~ 255
signed:
The highest bit is the sign bit 0+ 1-
1 Sign bit + 7 Digit
Complement operation ：
A complement to a positive number = Original code
A negative complement = Inverse code + 1
eg(8bit):
3 The binary representation of ：
Original code = b0000 0011
Complement code = b0000 0011
-3 The binary representation of :
Original code ：1000 0011
Inverse code ：0111 1100
Complement code ：1111 1101
4. Floating point type means
127.1234
Scientific enumeration
32bit: 1 Sign bit + 8 Exponential position + 23 Significant digit bit
64bit: 1 Sign bit + 11 Exponential position + 52 Significant digit bit
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