Java

java运行的特点¶

JIT编译器是一种动态编译技术，它将程序的一部分或者全部源代码或更常见的字节码在运行时编译成机器码，然后将编译后的代码替换原来的代码。
字节码（英语：Bytecode）通常指的是已经经过编译，但与特定机器代码无关，需要解释器转译后才能成为机器代码的中间代码(多为虚拟机代码)。典型应用为Java虚拟机里的Java bytecode。
主要优点是可以在运行时根据程序的运行情况进行优化，从而提高程序的执行效率。
字节码编译是跨平台的，便于移植的。
主要缺点是编译字节码导致的延迟和空间开销较大，因此只有在程序运行时间较长的情况下才能体现出优势。
是提前编译（AOT）和字节码解释器(python的实现)的结合体，它的执行效率介于两者之间。

Java Virtual Machine (JVM) is an abstract computing machine.
Java Runtime Environment (JRE) is an implementation of the JVM.
Java Development Kit (JDK) contains JRE along with various development tools like Java libraries, Java source compilers, Java debuggers, bundling and deployment tools.
Java SE: Java™ Platform Standard Edition 21 Development Kit - JDK™ 21
Just In Time compiler (JIT) is runs after the program has started executing, on the fly. It has access to runtime information and makes optimizations of the code for better performance.

download from website
But the first download choice java 21 SDK seems not contain Java Control Panel (javacpl.exe), you need to install Java SE Development Kit 8u381 which include JDK 1.8 and JRE 1.8
config Java Control Panel, add https://www.topcoder.com to allowed website (Attention: https)
open ContestAppletProd.jnlp
need 127.0.0.1 proxy and HTTP TUNE 1 to connect to server

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