README.md · teleis/mini-jvm

# [Mini-jvm](https://jvm.guxingke.com) [![Gitter](https://badges.gitter.im/guxingke/mini-jvm.svg)](https://gitter.im/guxingke/mini-jvm?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
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------
使用 Java 8 实现 JVM

## 特性

### 元循环(Metacircular)
mini-jvm on mini-jvm on hotspot. 可以在 mini-jvm 里运行 mini-jvm . 
```
$ java -jar jvm-core/target/mini-jvm.jar -jar jvm-core/target/mini-jvm.jar -jar test.jar
# Hello World!
```

## 动机

1. 尝试了解 JVM 原理, Learning by doing
2. 纸上得来终觉浅, 实践
3. 用简单的代码帮助 Javaer 理解 JVM

## 快速体验 [Macos 用户]

### Hello world

```bash
brew tap guxingke/repo && brew install mini-jvm

cat <<EOF > HelloWorld.java
public class HelloWorld {
  public static void main(String[] args) {
    if (args.length == 0) {
      System.out.println("hello");
      return;
    }

for(int i = 0; i < args.length; i ++) {
      System.out.println(args[i]);
    }
  }
}
EOF

javac HelloWorld.java

# no args
mini-jvm HelloWold
# => hello

# with program args
mini-jvm HelloWold hello mini-jvm
# =>  hello
# =>  mini-jvm

# 输入 mini-jvm -help 了解更多.
```

### 彩蛋 1 , 理解 JVM 基于栈的解释器.

```bash
cat <<EOF > Sum10.java
public class Sum10 {
  public static void main(String[] args) {
    int sum = sum10();
    System.out.println(sum);
  }
  
  public static int sum10() {
    int sum = 0;
    for (int i = 1; i <= 10; i++) {
      sum += i;
    }
    return sum;
  }
}
EOF

javac Sum10.java
java Sum10
# => 55

# 生成类汇编语言
# mini-jvm --bc [classfile] [method]
mini-jvm --bc Sum10.class sum10 > sum10.bc

# 解释上一步生成的 sum10.bc
# mini-jvm -- [bytecode file]
mini-jvm -- sum10.bc
# => 55

# ================================
```

## 快速体验 [其他操作系统]

需要自行下载打包. [Dev](https://jvm.guxingke.com/#/dev)

## 规划
- Class 文件解析 90%
- 字节码执行 90%
- 类加载 90%
- 方法调用 90%
- 实例化 90%
- Native 方法 90%
- 异常处理 60%
- self-booting 70%

## 局限
1. 不实现 GC
2. 不实现多线程

## 变更记录
- 实现了元循环(Metacircular)
- 反射特性基本可用
- 增加简单的调试器 bin/jdb.
- 支持 Lambda 调用, closure, currying 可用.
- Hello World 级别可用

## 个人记录
- [如何构建你自己的 JVM (2) Hello World](https://www.guxingke.com/posts/how-to-build-your-own-jvm-3.html)
- [如何构建你自己的 JVM (1) 解释器](https://www.guxingke.com/posts/how-to-build-your-own-jvm-2.html)
- [如何构建你自己的 JVM (0) 概述](https://www.guxingke.com/posts/how-to-build-your-own-jvm-1.html)
- [用 Java 实现一个简单的虚拟机 ?](https://www.guxingke.com/posts/mini-jvm-intro.html)

## 参考
- [The Java® Virtual Machine Specification](https://docs.oracle.com/javase/specs/jvms/se8/html/)
- [JVM 字节码从入门到精通](https://juejin.im/book/5c25811a6fb9a049ec6b23ee/)
- [自己动手写Java虚拟机](https://book.douban.com/subject/26802084/)

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