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This article mainly introduces "comparative analysis of performance examples of Java and C++". In daily operation, I believe that many people have doubts about the comparative analysis of performance examples of Java and C++. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts of "comparative analysis of performance examples of Java and C++". Next, please follow the editor to study!

1. Overview

Programming languages are classified according to their level of abstraction. We distinguish between high-level languages (Java,Python,JavaScript,C + +, Go), low-level languages (assemblers), and finally machine code.

Each high-level language code, such as Java, needs to be converted to machine native code before it can be executed. The translation process can be compiled or interpreted. But there is a third option. Try to take advantage of the combination of the two methods.

two。 Compilation and interpretation

Let's start looking at some of the differences between compiled and interpreted languages.

2.1 compiled language

The compiler converts the compiled language (C + +, Go) directly into machine code.

They require clear build steps before they can be executed. This is why you need to recompile the program every time you change the code.

Compiled languages tend to be faster and more efficient than interpreted languages. However, the machine code they generate is platform specific.

2.2 interpretive language

In interpreted language (Python,JavaScript), there are no build steps. Instead, the interpreter operates on the source code of the program when it executes the program.

It was once thought that interpreting languages is much slower than compiling languages. However, with the development of just-in-time compilation (JIT), the performance gap is narrowing. The JIT compiler converts code from an interpreting language to machine code while the program is running.

In addition, we can execute the interpreted language code on multiple platforms such as Windows,Linux or Mac. The interpretation code is not associated with a particular type of CPU architecture.

3. Write Once Run Anywhere

Java and JVM are designed with portability in mind. As a result, most popular platforms today can run Java code.

This seems to imply that Java is a purely interpretive language. However, before execution, the Java source code needs to be compiled into bytecode. Bytecode is a special machine language inherent in JVM. JVM interprets and executes this code at run time.

It is built and customized by JVM for every platform that supports Java and is not our program or library.

JVM also has a JIT compiler. This means that JVM optimizes our code at run time to gain similar performance advantages to compiled languages.

4. Java compiler

Javac's command-line tool compiles Java source code into platform-independent bytecode in Java class files (xxx.class):

$javac HelloWorld.java

Source code files have a .java suffix, while class files that contain bytecode have a .class suffix.

5. Java virtual machine

Compiled class files (bytecode), which can be executed by JVM:

$java HelloWorld Hello Java!

How to convert bytecode to machine native code at run time.

5.1 Architecture Overview

JVM consists of five parts:

Class loader

JVM memory structure

Executive engine

Local method interface

Local method library

5.2 Class Loader

JVM uses ClassLoader to load compiled class files into JVM memory

In addition to loading, ClassLoader also performs linking and initialization.

Verify whether there is a security vulnerability in the bytecode

Allocate memory for static variables

Replace symbolic memory references with original references

Assign the original value to a static variable

Execute all static code blocks

5.3 execution engine

The execution engine is responsible for reading the bytecode, converting it into machine native code and executing it.

Three main components are responsible for execution, including the interpreter and the compiler:

Because JVM is platform independent, it uses an interpreter to execute bytecode

The JIT compiler compiles bytecode to native code to improve performance at repeated method invocations.

The garbage collector collects and deletes all unreferenced objects.

The execution engine uses the native method interface (JNI) to invoke native libraries and applications.

5.4 just-in-time compiler (JIT)

The main disadvantage of the interpreter is that it needs to be interpreted and executed every time a method is called, which is slower than compiled native code. Java uses the JIT compiler to overcome this problem.

The JIT compiler cannot completely replace the interpreter. The execution engine is still using it. However, JVM uses the JIT compiler based on how often the method is called.

The JIT compiler compiles the bytecode of the entire method into machine native code, so it can be reused directly. Like a standard compiler, intermediate code is generated, optimized, and then machine native code is generated.

The profiler is a special component of the JIT compiler that is responsible for finding hot spots. JVM determines which code to compile based on the performance analysis information collected by the runtime.

The effect is that after several execution cycles, the Java program can perform its work faster. Once JVM learns about the hotspots, it can create native code to make it run faster.

6. Performance comparison

Let's take a look at how JIT compilation can improve the runtime performance of Java.

6.1 performance Test of Fibonacci sequence

We will use a simple recursive method to calculate the nth Fibonacci number:

Private static int fibonacci (int index) {if (index)

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