search
HomeJavaJavaBaseJava class loading process
Java class loading processJun 03, 2020 pm 05:58 PM
java

Java class loading process

Java class loading process

The first is the loading process (Loading), which is Java reading bytecode data from different data sources Get it into the JVM and map it to a data structure (Class object) recognized by the JVM. The data source here may be in various forms, such as jar files, class files, or even network data sources; if the input data is not a ClassFile structure, ClassFormatError will be thrown. The loading stage is the stage where users participate. We can customize the class loader to implement our own class loading process.

The second stage is Linking, which is the core step. Simply put, it is to smoothly transfer the original class definition information into the JVM running process. This can be further broken down into three steps: 1. Verification, which is an important guarantee for virtual machine security. The JVM needs to verify that the byte information complies with the Java virtual machine specification, otherwise it will be considered a VerifyError, thus preventing If malicious information or non-compliant information harms the operation of the JVM, the verification phase may trigger the loading of more classes. 2. Preparation (Pereparation), create static variables in the class or interface, and initialize the initial values ​​of the static variables. But there is a difference between the "initialization" here and the display initialization phase below. The focus is on allocating the required memory space and will not execute further JVM instructions. 3. Resolution. In this step, the symbolic reference in the constant pool will be replaced with a direct reference. In the Java Virtual Machine Specification, the analysis of various aspects such as classes, interfaces, methods and fields is introduced in detail.

The last step is the initialization phase (initialization). This step actually executes the code logic of class initialization, including the action of static field assignment, and the execution of the logic in the static initialization block in the class definition. The compiler performs the compilation phase This part of the logic will be sorted out, and the initialization logic of the parent type will take precedence over the logic of the current type. Let’s talk about the parent delegation model. Simply put, when the loader (Class-Loader) tries to load a certain type, unless the parent class loader cannot find the corresponding type, try to delegate the task to the parent of the current loader. Tools to do it. The purpose of using the delegation model is to avoid repeated loading of Java types.

Common scenarios of custom class loaders

To achieve similar in-process isolation, the class loader is actually used as a different namespace, as well as to provide similar containers and modules transformation effect. For example: 1. Two modules depend on different versions of a certain class library. If they are loaded by different containers, they will not interfere with each other. Masters in this area are Java EE and OSGL, JPMS and other frameworks. 2. The application needs to obtain class definition information from different data sources, such as network data sources instead of the local file system. 3. Or you need to manipulate the bytecode yourself and dynamically modify the generated type.

We can generally simply understand the custom class loading process: 1. Find its binary implementation by specifying the name. This is often the part that the custom class loader will "customize", for example, in a specific data source Get bytecode by name, or modify or generate bytecode. 2. Then, create the Class object and complete the class loading process. The conversion of binary information into class objects usually relies on defineClass. We do not need to implement it ourselves. It is a final method. With the Class object, the subsequent loading process will be completed smoothly.

Recommended tutorial: "Java Tutorial"

The above is the detailed content of Java class loading process. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
带你搞懂Java结构化数据处理开源库SPL带你搞懂Java结构化数据处理开源库SPLMay 24, 2022 pm 01:34 PM

本篇文章给大家带来了关于java的相关知识,其中主要介绍了关于结构化数据处理开源库SPL的相关问题,下面就一起来看一下java下理想的结构化数据处理类库,希望对大家有帮助。

Java集合框架之PriorityQueue优先级队列Java集合框架之PriorityQueue优先级队列Jun 09, 2022 am 11:47 AM

本篇文章给大家带来了关于java的相关知识,其中主要介绍了关于PriorityQueue优先级队列的相关知识,Java集合框架中提供了PriorityQueue和PriorityBlockingQueue两种类型的优先级队列,PriorityQueue是线程不安全的,PriorityBlockingQueue是线程安全的,下面一起来看一下,希望对大家有帮助。

完全掌握Java锁(图文解析)完全掌握Java锁(图文解析)Jun 14, 2022 am 11:47 AM

本篇文章给大家带来了关于java的相关知识,其中主要介绍了关于java锁的相关问题,包括了独占锁、悲观锁、乐观锁、共享锁等等内容,下面一起来看一下,希望对大家有帮助。

一起聊聊Java多线程之线程安全问题一起聊聊Java多线程之线程安全问题Apr 21, 2022 pm 06:17 PM

本篇文章给大家带来了关于java的相关知识,其中主要介绍了关于多线程的相关问题,包括了线程安装、线程加锁与线程不安全的原因、线程安全的标准类等等内容,希望对大家有帮助。

详细解析Java的this和super关键字详细解析Java的this和super关键字Apr 30, 2022 am 09:00 AM

本篇文章给大家带来了关于Java的相关知识,其中主要介绍了关于关键字中this和super的相关问题,以及他们的一些区别,下面一起来看一下,希望对大家有帮助。

Java基础归纳之枚举Java基础归纳之枚举May 26, 2022 am 11:50 AM

本篇文章给大家带来了关于java的相关知识,其中主要介绍了关于枚举的相关问题,包括了枚举的基本操作、集合类对枚举的支持等等内容,下面一起来看一下,希望对大家有帮助。

java中封装是什么java中封装是什么May 16, 2019 pm 06:08 PM

封装是一种信息隐藏技术,是指一种将抽象性函式接口的实现细节部分包装、隐藏起来的方法;封装可以被认为是一个保护屏障,防止指定类的代码和数据被外部类定义的代码随机访问。封装可以通过关键字private,protected和public实现。

归纳整理JAVA装饰器模式(实例详解)归纳整理JAVA装饰器模式(实例详解)May 05, 2022 pm 06:48 PM

本篇文章给大家带来了关于java的相关知识,其中主要介绍了关于设计模式的相关问题,主要将装饰器模式的相关内容,指在不改变现有对象结构的情况下,动态地给该对象增加一些职责的模式,希望对大家有帮助。

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

Safe Exam Browser

Safe Exam Browser

Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

SAP NetWeaver Server Adapter for Eclipse

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!