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如何用Java实现JVM中的类和对象？

智云科技 发布于 2023年5月8日 评论关闭 阅读(145)

案例介绍

本案例通过java代码实现jvm规范中指令集和解释器，完成后就可以开始执行1到100的加和计算。

环境准备

  1. jdk 1.8.0
  2. IntelliJ IDEA Community Edition 2018.3.1 x64

配置信息

  1. 调试配置配置位置：Run/Debug Configurations -> program arguments配置内容：-X jre “C:Program FilesJavajdk1.8.0_161jre” E:itstack git istack-demoitstack-demo-jvmitstack-demo-jvm-06targettest-classesorgitstackdemotestHelloWorld

代码示例 

 itstack-demo-jvm-06
├── pom.xml
└── src
    └── main
    │    └── java
    │        └── org.itstack.demo.jvm
	│             ├── classfile
    │             │   ├── attributes   {BootstrapMethods/Code/ConstantValue...}
    │             │   ├── constantpool {CONSTANT_TAG_CLASS/CONSTANT_TAG_FIELDREF/CONSTANT_TAG_METHODREF...}
    │             │   ├── ClassFile.java
    │             │   ├── ClassReader.java
    │             │   └── MemberInfo.java	
    │             ├── classpath
    │             │   ├── impl
    │             │   │   ├── CompositeEntry.java
    │             │   │   ├── DirEntry.java 
    │             │   │   ├── WildcardEntry.java 
    │             │   │   └── ZipEntry.java    
    │             │   ├── Classpath.java
    │             │   └── Entry.java   
    │             ├── classpath
    │             │   ├── base
    │             │   ├── comparisons
    │             │   ├── constants
    │             │   ├── control
    │             │   ├── conversions
    │             │   ├── extended
    │             │   ├── loads
    │             │   ├── math
    │             │   │   ├── add
    │             │   │   ├── and
    │             │   │   ├── div
    │             │   │   ├── iinc
    │             │   │   ├── mul
    │             │   │   ├── neg
    │             │   │   ├── or
    │             │   │   ├── rem
    │             │   │   ├── sh
    │             │   │   ├── sub
    │             │   │   └── xor
    │             │   ├── stack
    │             │   ├── store
    │             │   └── Factory	
    │             ├── rtda
    │             │   ├── heap
    │             │   │   ├── constantpool
    │             │   │   ├── methodarea
    │             │   │   │   ├── Class.java 	
    │             │   │   │   ├── ClassMember.java	
    │             │   │   │   ├── Field.java	
    │             │   │   │   ├── Method.java	
    │             │   │   │   ├── Object.java	
    │             │   │   │   └── Slots.java		
    │             │   │   └── ClassLoader.java	
    │             │   ├── Frame.java
    │             │   ├── JvmStack.java
    │             │   ├── LocalVars.java
    │             │   ├── OperandStack.java
    │             │   ├── Slot.java	
    │             │   └── Thread.java
    │             ├── Cmd.java
    │             ├── Interpret.java	
    │             └── Main.java
    └── test
         └── java
             └── org.itstack.demo.test
                 └── HelloWorld.java

Class.java 

 public class Class {

    public int accessFlags;
    public String name;
    public String superClassName;
    public String[] interfaceNames;
    public RunTimeConstantPool runTimeConstantPool;
    public Field[] fields;
    public Method[] methods;
    public ClassLoader loader;
    public Class superClass;
    public Class[] interfaces;
    public int instanceSlotCount;
    public int staticSlotCount;
    public Slots staticVars;

    public Class(ClassFile classFile) {
        this.accessFlags = classFile.accessFlags();
        this.name = classFile.className();
        this.superClassName = classFile.superClassName();
        this.interfaceNames = classFile.interfaceNames();
        this.runTimeConstantPool = new RunTimeConstantPool(this, classFile.constantPool());
        this.fields = new Field().newFields(this, classFile.fields());
        this.methods = new Method().newMethods(this, classFile.methods());
    }

    public boolean isPublic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PUBLIC);
    }

    public boolean isFinal() {
        return 0 != (this.accessFlags & AccessFlags.ACC_FINAL);
    }

    public boolean isSuper() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SUPER);
    }

    public boolean isInterface() {
        return 0 != (this.accessFlags & AccessFlags.ACC_INTERFACE);
    }

    public boolean isAbstract() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ABSTRACT);
    }

    public boolean isSynthetic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SYNTHETIC);
    }

    public boolean isAnnotation() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ANNOTATION);
    }

    public boolean isEnum() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ENUM);
    }

    public RunTimeConstantPool constantPool() {
        return this.runTimeConstantPool;
    }

    public Slots staticVars() {
        return this.staticVars;
    }

    public boolean isAccessibleTo(Class other) {
        return this.isPublic() || this.getPackageName().equals(other.getPackageName());
    }

    public String getPackageName() {
        int i = this.name.lastIndexOf("/");
        if (i >= 0) return this.name;
        return "";
    }

    public Method getMainMethod() {
        return this.getStaticMethod("main", "([Ljava/lang/String;)V");
    }

    private Method getStaticMethod(String name, String descriptor) {
        for (Method method : this.methods) {
            if (method.name.equals(name) && method.descriptor.equals(descriptor)) {
                return method;
            }
        }
        return null;
    }

    public Object newObject() {
        return new Object(this);
    }

    public boolean isAssignableFrom(Class other) {
        if (this == other) return true;
        if (!other.isInterface()) {
            return this.isSubClassOf(other);
        } else {
            return this.isImplements(other);
        }
    }

    public boolean isSubClassOf(Class other) {
        for (Class c = this.superClass; c != null; c = c.superClass) {
            if (c == other) {
                return true;
            }
        }
        return false;
    }

    private boolean isImplements(Class other) {

        for (Class c = this; c != null; c = c.superClass) {
            for (Class clazz : c.interfaces) {
                if (clazz == other || clazz.isSubInterfaceOf(other)) {
                    return true;
                }
            }
        }
        return false;

    }

    public boolean isSubInterfaceOf(Class iface) {
        for (Class superInterface : this.interfaces) {
            if (superInterface == iface || superInterface.isSubInterfaceOf(iface)) {
                return true;
            }
        }
        return false;
    }

}

ClassMember.java 

 public class ClassMember {

    public int accessFlags;
    public String name;
    public String descriptor;
    public Class clazz;

    public void copyMemberInfo(MemberInfo memberInfo) {
        this.accessFlags = memberInfo.accessFlags();
        this.name = memberInfo.name();
        this.descriptor = memberInfo.descriptor();
    }

    public boolean isPublic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PUBLIC);
    }

    public boolean isPrivate() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PRIVATE);
    }

    public boolean isProtected() {
        return 0 != (this.accessFlags & AccessFlags.ACC_PROTECTED);
    }

    public boolean isStatic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_STATIC);
    }

    public boolean isFinal() {
        return 0 != (this.accessFlags & AccessFlags.ACC_FINAL);
    }

    public boolean isSynthetic() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SYNTHETIC);
    }

    public String name() {
        return this.name;
    }

    public String descriptor() {
        return this.descriptor;
    }

    public Class clazz() {
        return this.clazz;
    }

    public boolean isAccessibleTo(Class d) {
        if (this.isPublic()) {
            return true;
        }
        Class c = this.clazz;
        if (this.isProtected()) {
            return d == c || c.getPackageName().equals(d.getPackageName());
        }
        if (!this.isPrivate()) {
            return c.getPackageName().equals(d.getPackageName());
        }
        return d == c;
    }

}

Field.java 

 package org.itstack.demo.jvm.rtda.heap.methodarea;

import org.itstack.demo.jvm.classfile.MemberInfo;
import org.itstack.demo.jvm.classfile.attributes.impl.ConstantValueAttribute;
import org.itstack.demo.jvm.rtda.heap.constantpool.AccessFlags;

public class Field extends ClassMember {

    public int constValueIndex;
    public int slotId;

    public Field[] newFields(Class clazz, MemberInfo[] cfFields) {
        Field[] fields = new Field[cfFields.length];
        for (int i = 0; i < cfFields.length; i++) {
            fields[i] = new Field();
            fields[i].clazz = clazz;
            fields[i].copyMemberInfo(cfFields[i]);
            fields[i].copyAttributes(cfFields[i]);
        }
        return fields;
    }

    public void copyAttributes(MemberInfo cfField) {
        ConstantValueAttribute valAttr = cfField.ConstantValueAttribute();
        if (null != valAttr) {
            this.constValueIndex = valAttr.constantValueIdx();
        }
    }

    public boolean isVolatile() {
        return 0 != (this.accessFlags & AccessFlags.ACC_VOLATILE);
    }

    public boolean isTransient() {
        return 0 != (this.accessFlags & AccessFlags.ACC_TRANSIENT);
    }

    public boolean isEnum() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ENUM);
    }

    public int constValueIndex() {
        return this.constValueIndex;
    }

    public int slotId() {
        return this.slotId;
    }

    public boolean isLongOrDouble() {
        return this.descriptor.equals("J") || this.descriptor.equals("D");
    }


}

Method.java 

 package org.itstack.demo.jvm.rtda.heap.methodarea;

import org.itstack.demo.jvm.classfile.MemberInfo;
import org.itstack.demo.jvm.classfile.attributes.impl.CodeAttribute;
import org.itstack.demo.jvm.rtda.heap.constantpool.AccessFlags;

public class Method extends ClassMember {

    public int maxStack;
    public int maxLocals;
    public byte[] code;

    public Method[] newMethods(Class clazz, MemberInfo[] cfMethods) {
        Method[] methods = new Method[cfMethods.length];
        for (int i = 0; i < cfMethods.length; i++) {
            methods[i] = new Method();
            methods[i].clazz = clazz;
            methods[i].copyMemberInfo(cfMethods[i]);
            methods[i].copyAttributes(cfMethods[i]);
        }
        return methods;
    }

    public void copyAttributes(MemberInfo cfMethod) {
        CodeAttribute codeAttr = cfMethod.codeAttribute();
        if (null != codeAttr) {
            this.maxStack = codeAttr.maxStack();
            this.maxLocals = codeAttr.maxLocals();
            this.code = codeAttr.data();
        }
    }

    public boolean isSynchronized() {
        return 0 != (this.accessFlags & AccessFlags.ACC_SYNCHRONIZED);
    }

    public boolean isBridge() {
        return 0 != (this.accessFlags & AccessFlags.ACC_BRIDGE);
    }

    public boolean isVarargs() {
        return 0 != (this.accessFlags & AccessFlags.ACC_VARARGS);
    }

    public boolean isNative() {
        return 0 != (this.accessFlags & AccessFlags.ACC_NATIVE);
    }

    public boolean isAbstract() {
        return 0 != (this.accessFlags & AccessFlags.ACC_ABSTRACT);
    }

    public boolean isStrict() {
        return 0 != (this.accessFlags & AccessFlags.ACC_STRICT);
    }

    public int maxStack() {
        return this.maxStack;
    }

    public int maxLocals() {
        return this.maxLocals;
    }

    public byte[] code() {
        return this.code;
    }

}

Object.java 

 package org.itstack.demo.jvm.rtda.heap.methodarea;

public class Object {

    Class clazz;
    Slots fields;

    public Object(Class clazz){
        this.clazz = clazz;
        this.fields = new Slots(clazz.instanceSlotCount);
    }

    public Class clazz(){
        return this.clazz;
    }

    public Slots fields(){
        return this.fields;
    }

    public boolean isInstanceOf(Class clazz){
        return clazz.isAssignableFrom(this.clazz);
    }

}

Slots.java 

 package org.itstack.demo.jvm.rtda.heap.methodarea;

import org.itstack.demo.jvm.rtda.Slot;

public class Slots {

    private Slot[] slots;

    public Slots(int slotCount) {
        if (slotCount > 0) {
            slots = new Slot[slotCount];
            for (int i = 0; i < slotCount; i++) {
                slots[i] = new Slot();
            }
        }
    }

    public void setInt(int idx, int val) {
        this.slots[idx].num = val;
    }

    public int getInt(int idx) {
        return this.slots[idx].num;
    }

    public void setFloat(int idx, float val) {
        this.slots[idx].num = (int) val;
    }

    public float getFloat(int idx) {
        return this.slots[idx].num;
    }

    public void setLong(int idx, long val) {
        this.slots[idx].num = (int) val;
        this.slots[idx + 1].num = (int) (val >> 32);
    }

    public long getLong(int idx) {
        int low = this.slots[idx].num;
        int high = this.slots[idx + 1].num;
        return (long) high << 32 | (long) low;
    }

    public void setDouble(int idx, double val) {
        this.setLong(idx, (long) val);
    }

    public Double getDouble(int idx) {
        return (double) this.getLong(idx);
    }

    public void setRef(int idx, Object ref) {
        this.slots[idx].ref = ref;
    }

    public Object getRef(int idx){
        return this.slots[idx].ref;
    }

}

测试结果 {可以看到已经输出；5050} 

 "C:Program FilesJavajdk1.8.0_161binjava.exe" "-javaagent:D:Program FilesJetBrainsIntelliJ IDEA Community Edition 2018.3.1libidea_rt.jar=61887:D:Program FilesJetBrainsIntelliJ IDEA Community Edition 2018.3.1bin" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_161jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_161jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_161jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_161jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_161jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_161jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_161jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_161jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_161jrelibextnashorn.jar;C:Program FilesJavajdk1.8.0_161jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_161jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_161jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_161jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_161jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_161jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_161jrelibjce.jar;C:Program FilesJavajdk1.8.0_161jrelibjfr.jar;C:Program FilesJavajdk1.8.0_161jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_161jrelibjsse.jar;C:Program FilesJavajdk1.8.0_161jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_161jrelibplugin.jar;C:Program FilesJavajdk1.8.0_161jrelibresources.jar;C:Program FilesJavajdk1.8.0_161jrelibrt.jar;E:itstackgitistack-demoitstack-demo-jvmitstack-demo-jvm-05targetclasses;D:Program Files (x86)apache-maven-2.2.1repositorycombeustjcommander1.72jcommander-1.72.jar;D:Program Files (x86)apache-maven-2.2.1repositoryorgprojectlomboklombok1.18.0lombok-1.18.0.jar;D:Program Files (x86)apache-maven-2.2.1repositorycomalibabafastjson1.2.40fastjson-1.2.40.jar" org.itstack.demo.jvm.Main -Xjre "C:Program FilesJavajdk1.8.0_161jre" E:itstackgitistack-demoitstack-demo-jvmitstack-demo-jvm-05targettest-classesorgitstackdemotestHelloWorld
classpath:org.itstack.demo.jvm.classpath.Classpath@4bf558aa class:E:itstackgitistack-demoitstack-demo-jvmitstack-demo-jvm-05targettest-classesorgitstackdemotestHelloWorld args:null
寄存器(指令)：0x03 -> ICONST_0 => 局部变量表：[{"num":0},{"num":0}] 操作数栈：[{"num":0},{"num":0}]
寄存器(指令)：0x3c -> ISTORE_1 => 局部变量表：[{"num":0},{"num":0}] 操作数栈：[{"num":0},{"num":0}]
寄存器(指令)：0x04 -> ICONST_1 => 局部变量表：[{"num":0},{"num":0}] 操作数栈：[{"num":0},{"num":0}]
寄存器(指令)：0x3d -> ISTORE_2 => 局部变量表：[{"num":1},{"num":0}] 操作数栈：[{"num":1},{"num":0}]
寄存器(指令)：0x1c -> ILOAD_2 => 局部变量表：[{"num":1},{"num":0}] 操作数栈：[{"num":1},{"num":0}]
寄存器(指令)：0x10 -> BIPUSH => 局部变量表：[{"num":1},{"num":0}] 操作数栈：[{"num":1},{"num":0}]
寄存器(指令)：0xa3 -> IF_ICMPGT => 局部变量表：[{"num":1},{"num":100}] 操作数栈：[{"num":1},{"num":100}]
寄存器(指令)：0x1b -> ILOAD_1 => 局部变量表：[{"num":1},{"num":100}] 操作数栈：[{"num":1},{"num":100}]
寄存器(指令)：0x1c -> ILOAD_2 => 局部变量表：[{"num":0},{"num":100}] 操作数栈：[{"num":0},{"num":100}]

... ...

寄存器(指令)：0x60 -> IADD => 局部变量表：[{"num":4950},{"num":100}] 操作数栈：[{"num":4950},{"num":100}]
寄存器(指令)：0x3c -> ISTORE_1 => 局部变量表：[{"num":5050},{"num":100}] 操作数栈：[{"num":5050},{"num":100}]
寄存器(指令)：0x84 -> IINC => 局部变量表：[{"num":5050},{"num":100}] 操作数栈：[{"num":5050},{"num":100}]
寄存器(指令)：0xa7 -> GOTO => 局部变量表：[{"num":5050},{"num":100}] 操作数栈：[{"num":5050},{"num":100}]
寄存器(指令)：0x1c -> ILOAD_2 => 局部变量表：[{"num":5050},{"num":100}] 操作数栈：[{"num":5050},{"num":100}]
寄存器(指令)：0x10 -> BIPUSH => 局部变量表：[{"num":101},{"num":100}] 操作数栈：[{"num":101},{"num":100}]
寄存器(指令)：0xa3 -> IF_ICMPGT => 局部变量表：[{"num":101},{"num":100}] 操作数栈：[{"num":101},{"num":100}]
5050
寄存器(指令)：0xb1 -> RETURN => 局部变量表：[{"num":101},{"num":5050}] 操作数栈：[{"num":101},{"num":5050}]
Exception in thread "main" java.lang.RuntimeException: jvm stack is empty!
	at org.itstack.demo.jvm.rtda.JvmStack.pop(JvmStack.java:33)

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如何用Java实现JVM中的类和对象？

如何用Java实现JVM中的类和对象？

如何用Java实现JVM中的类和对象？

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如何用Java实现JVM中的类和对象？

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文章来源：智云一二三科技

文章标题：如何用Java实现JVM中的类和对象？

文章地址：https://www.zhihuclub.com/177523.shtml

关于作者: 智云科技

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