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<>一、对象创建过程
1.loading:加载对应类class文件。
2.linking:验证文件格式(verification)、为类的静态变量分配内存,并初始化为默认值(preparation)、将符号引用转成直接引用(resolution)。
3.initializing:初始化过程为类的静态变量赋予正确的初始值.
4.为对象分配内存。
5.成员变量赋默认值。
6.调用构造方法:成员变量赋默初始值,其他语句。
<>二、对象结构
1.对象头:Mark Word(标记字段)、Class Pointer(类型指针)。其中 Class
Pointer是虚拟机用来通过这个指针来确定这个对象是哪个类的实例,Mark
Word用于存储对象自身的运行时数据,如:哈希码、GC分代年龄、锁状态标志、线程id等。
2.实例数据:存放类的属性数据信息,包括父类的属性信息。
3.填充数据:由于虚拟机要求对象起始地址必须是8字节的整数倍,用来填充。
数组对象会多一个四字节的数组长度。
<>三、对象在内存大小
Object object = new Object();
Mark Word(标记字段):8字节。
Class Pointer(类型指针):4字节。
一共8+4=12字节,但不是8的倍数,会填充到16字节。
<>四.对象分配过程
1.new一个对象,先判断栈是否可以存储下,如果可以分配在栈,出队就清除掉对象了。
2.如果栈存储不下,大对象直接存储在堆内存年老代中,直到MajorGC时清除。
3.小对象存放在Eden伊甸园区,Minor GC如果对象未清除,转移到survivor的两块区域,满足年龄转移到年老代。