package com.prototype;public class Prototype implements Cloneable {private int x;private int y;private int z;public Prototype() {this.x = 2;this.y = 3;this.z = 4;}public void change() {this.x = 9;this.y = 8;this.z = 7;}public Prototype clone() {Object object = null;try {object = super.clone();} catch (CloneNotSupportedException exception) {throw new RuntimeException(exception);}return (Prototype) object;}public String toString() {return "[" + x + "," + y + "," + z + "]";}public static void main(String[] args) {Prototype prototype1 = new Prototype();prototype1.change();System.out.println(prototype1);Prototype prototype2 = prototype1.clone();System.out.println(prototype2);}}

package com.prototype;class Field{private int a;public int getA() {return a;}public void setA(int a) {this.a = a;}}public class ShallowPrototype implements Cloneable {private int x;private int y;private int z;private Field field;public ShallowPrototype() {this.x = 2;this.y = 3;this.z = 4;this.field = new Field();this.field.setA(5);}public Field getField() {return field;}public ShallowPrototype clone() {Object object = null;try {object = super.clone();} catch (CloneNotSupportedException exception) {throw new RuntimeException(exception);}return (ShallowPrototype) object;}public String toString() {return "[" + x + "," + y + "," + z + "," + field.getA() + "]";}public static void main(String[] args) {ShallowPrototype prototype1 = new ShallowPrototype();System.out.println(prototype1);System.out.println(prototype1.getField());ShallowPrototype prototype2 = prototype1.clone();System.out.println(prototype2);System.out.println(prototype2.getField());}}

package com.prototype;class Field implements Cloneable{private int a;public int getA() {return a;}public void setA(int a) {this.a = a;}protected Field clone() {Object object = null;try {object = super.clone();} catch (CloneNotSupportedException exception) {throw new RuntimeException(exception);}return (Field) object;}}public class DeepPrototype implements Cloneable {private int x;private int y;private int z;private Field field;public DeepPrototype() {this.x = 2;this.y = 3;this.z = 4;this.field = new Field();this.field.setA(5);}public Field getField() {return field;}protected DeepPrototype clone() {Object object = null;try {object = super.clone();((DeepPrototype)object).field = this.field.clone();} catch (CloneNotSupportedException exception) {throw new RuntimeException(exception);}return (DeepPrototype) object;}public String toString() {return "[" + x + "," + y + "," + z + "," + field.getA() + "]";}public static void main(String[] args) {DeepPrototype prototype1 = new DeepPrototype();System.out.println(prototype1);System.out.println(prototype1.getField());DeepPrototype prototype2 = prototype1.clone();System.out.println(prototype2);System.out.println(prototype2.getField());}}

JVM_ENTRY(jobject, JVM_Clone(JNIEnv* env, jobject handle))JVMWrapper("JVM_Clone");Handle obj(THREAD, JNIHandles::resolve_non_null(handle));const KlassHandle klass (THREAD, obj->klass());JvmtiVMObjectAllocEventCollector oam;#ifdef ASSERT// Just checking that the cloneable flag is set correctif (obj->is_javaArray()) {guarantee(klass->is_cloneable(), "all arrays are cloneable");} else {guarantee(obj->is_instance(), "should be instanceOop");bool cloneable = klass->is_subtype_of(SystemDictionary::Cloneable_klass());guarantee(cloneable == klass->is_cloneable(), "incorrect cloneable flag");}
#endif// Check if class of obj supports the Cloneable interface.// All arrays are considered to be cloneable (See JLS 20.1.5)if (!klass->is_cloneable()) {//这里检查了是否实现了Cloneable接口，如果没实现，会抛出异常CloneNotSupportException。
    ResourceMark rm(THREAD);THROW_MSG_0(vmSymbols::java_lang_CloneNotSupportedException(), klass->external_name());}// Make shallow object copyconst int size = obj->size();//取对象大小oop new_obj = NULL;if (obj->is_javaArray()) {//如果是数组const int length = ((arrayOop)obj())->length();//取长度new_obj = CollectedHeap::array_allocate(klass, size, length, CHECK_NULL);//分配内存，写入元数据信息} else {new_obj = CollectedHeap::obj_allocate(klass, size, CHECK_NULL);//分配内存，写入元数据信息
  }// 4839641 (4840070): We must do an oop-atomic copy, because if another thread// is modifying a reference field in the clonee, a non-oop-atomic copy might// be suspended in the middle of copying the pointer and end up with parts// of two different pointers in the field.  Subsequent dereferences will crash.// 4846409: an oop-copy of objects with long or double fields or arrays of same// won't copy the longs/doubles atomically in 32-bit vm's, so we copy jlongs instead// of oops.  We know objects are aligned on a minimum of an jlong boundary.// The same is true of StubRoutines::object_copy and the various oop_copy// variants, and of the code generated by the inline_native_clone intrinsic.assert(MinObjAlignmentInBytes >= BytesPerLong, "objects misaligned");Copy::conjoint_jlongs_atomic((jlong*)obj(), (jlong*)new_obj,(size_t)align_object_size(size) / HeapWordsPerLong);//这一步就是真正的COPY内存块了// Clear the headernew_obj->init_mark();//初始化对象头，里面包含了Hashcode，GC信息，锁信息等，因为拷贝出的对象是一个全新的对象，所以这些信息需要初始化一下。// Store check (mark entire object and let gc sort it out)BarrierSet* bs = Universe::heap()->barrier_set();assert(bs->has_write_region_opt(), "Barrier set does not have write_region");bs->write_region(MemRegion((HeapWord*)new_obj, size));//write_region最终的实现在一个虚方法里，相当于JAVA的抽象方法，LZ没找到实现。暂不发表意见。// Caution: this involves a java upcall, so the clone should be// "gc-robust" by this stage.if (klass->has_finalizer()) {//如果有finalize方法，则需要注册一下。assert(obj->is_instance(), "should be instanceOop");new_obj = instanceKlass::register_finalizer(instanceOop(new_obj), CHECK_NULL);}return JNIHandles::make_local(env, oop(new_obj));//将内存对象转换成JAVA本地对象返回
JVM_END

void _Copy_conjoint_jlongs_atomic(jlong* from, jlong* to, size_t count) {if (from > to) {jlong *end = from + count;while (from < end)os::atomic_copy64(from++, to++);}else if (from < to) {jlong *end = from;from += count - 1;to   += count - 1;while (from >= end)os::atomic_copy64(from--, to--);}}