每天打开笔记本后都要回想今天是星期几，看了右下角的日历才知道。
The day before yesterday · HelloWorld can't be run this morning. Back to the foundation when he was 24 years old.
C: \ Users \ 10644> D:
D:> javac HelloWorld.java
HelloWorld.java:9: Error:
Unmappable character encoding GBK (0x82) System.out.println (“HelloWorld: ⱁ 粖 粖 澶 ╁ 紑 濮 嫔 抔 爅 ava 銆? ");
1 error
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D:>java HelloWorld
Error: A JNI error has occurred, please check your installation and try again
Exception in thread “main” java.lang.UnsupportedClassVersionError: HelloWorld has been compiled by a more recent version of the Java Runtime (class file version 57.0), this version of the Java Runtime only recognizes class file versions up to 52.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)
=======================================================
The reason for the above error reported on the Internet is that the java and avac versions are inconsistent, and multiple versions are installed on the computer.
Enter the control panel, delete java8 and keep java13.
========================================================
C:\Users\10644>javac --version
javac 13.0.2
C:\Users\10644>java --version
java 13.0.2 2020-01-14
Java™ SE Runtime Environment (build 13.0.2+8)
Java HotSpot™ 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)
C:\Users\10644>javac --version
javac 13.0.2
========================================================
C: \ Users \ 10644> D:
D:> javac HelloWorld.java
D:> java HelloWorld
HelloWorld, start learning java today.
========================================================
Register
Register is a storage component, the capacity is very limited, the size of the data that can be stored, now there are generally two kinds, that is, we often hear 32-bit and 64-bit, 32-bit registers can store 4 bytes Data, a 64-bit register can store 8 bytes of data. In addition, the CPU is divided into 32-bit and 64-bit, which is actually determined by the number of registers in it. It is conceivable that even 64-bit registers There is no big deal to be done, so ah, the current CPU generally has a lot of registers built in, so as to complete more complicated operations
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Copyright Notice: This article is CSDN The original article of the blogger "ithuangqing" follows the copyright agreement of CC 4.0 BY-SA. For reprinting, please attach the original source link and this statement.
Original link: https://blog.csdn.net/sinat_33921105/article/details/104047172
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Continuous learning of Java core knowledge, in-depth study of basic computer knowledge
As soon as I come up, I will ask about the principle and the index optimization of hundreds of millions of MySQL tables.
Why is the data structure a B + tree?
What is called back table, index coverage, leftmost match, and index pushdown
like fuzzy matching won't go index
powershell
=========================================================
public class HelloWorld
{
public static void main(String[] args）
{
byte a = 10;
int b = 200;
byte c = (byte) (a+b);
int d = a+b;
System.out.println©;
System.out.println(d);
}
}
Complement operation
AMD AMD64, based on Opteron processor, compatible with 32-bit applications, the software version of this mode is called xxx for x86-64 or amd64.
======================================================
1. Have you seen the source code?
2. Can you talk about the realization principle of HashMap?
3. When will HashMap rehash?
4. Combining the source code to talk about why HashMap has an endless loop in high concurrency scenarios?
5. What performance optimizations have been made to HashMap in JDK1.8?
6. What is the difference between HashMap and HashTable?
7. What is the difference between HashMap and ConcurrentHashMap?
8. What is the difference between ConcurrentHashMap and LinkedHashMap?
9. Why is the threshold of linked list to red-black tree in ConcurrentHashMap 8?
10. Have you seen other source code? Do you know the source code of Spring?
11. What about SpringBoot's source code? Do you know how the starter is implemented?
======================================================
https://blog.csdn.net/WantFlyDaCheng/article/details/105039855
One story tells how the CPU works
======================================================
https://blog.csdn.net/K17010/article/details/81126008?depth_1-utm_source=distribute.pc_relevant.none-task&utm_source=distribute.pc_relevant.none-task
assembly language personal study notes-Chapter 2 registers (CPU Working principle) Part 2
How to access Baidu homepage on Linux system.
exec 8 <> /dev/tcp/www.baidu.com/80
What is microservices.
cd /proc/$$/fd
exec 8>& -
What is http protocol
echo -e "get / http/1.0\n
ls./
ls./ 1> ~/ls.out
What is tcp protocol.
Connection-oriented reliable transmission protocol.
Relearn the handshake three times. Break up four times, wave four times. socket, socket.
tcpdump -nn -i eth0 port 80 capture packet
What is the switch and how to establish the socket.
https://blog.csdn.net/coderising/article/details/103776109?depth_1-utm_source=distribute.pc_relevant.none-task&utm_source=distribute.pc_relevant.none-task The
world's most powerful network equipment, the price is low, its appearance is not ...
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a successful hacker spoofing attacks, did not think the outcome is so sad reminder
