Class loading process and objects created

A Class loading process

In java class loading means to load the information into the memory classes . And only the first time will be loaded when using this class.
A category information includes the following components:

1. Class variables (static variables);
2. Class initialization code:
   - defining static assignment statement when the variable
   - a static initializer block
3. Class methods (static methods);
4. Instance variables;
5. Example initialization code:
   - assignment statement when the instance variables defined
   - Example initializer block
   - Constructor
6. Examples of the method;
7. The parent class information reference.

Class loading process includes:

1. Memory allocation information stored class;
2. The default value assigned to the class variable;
3. Load the parent class;
4. Set parent-child relationship;
5. Perform class initialization code.

Stack and heap memory is divided into, the stack for local variables, the storage dynamically allocated heap object , there is a memory area called method area, store information such .

After loading, java method area will have a copy of the information in this class.
Examples are as follows:

public class Base {
	public static int s;
	private int a;
	static {
		System.out.println("基类静态代码块，s：" + s);
		s = 1;
	}
	{
		System.out.println("基类实例代码块，a：" + a);
		a = 1;
	}

	public Base() {
		System.out.println("基类构造方法，a：" + a);
		a = 2;
	}

	protected void step() {
		System.out.println("base s：" + s + "，a：" + a);
	}

	public void action() {
		System.out.println("start");
		step();
		System.out.println("end");
	}
}

public class Child extends Base {
	public static int s;
	private int a;
	static {
		System.out.println("子类静态代码块，s：" + s);
		s = 10;
	}
	{
		System.out.println("子类实例代码块，a：" + a);
		a = 10;
	}

	public Child() {
		System.out.println("子类构造方法，a：" + a);
		a = 20;
	}

	protected void step() {
		System.out.println("child s：" + s + "，a：" + a);
	}

	public static void main(String[] args) {
		System.out.println("---- new Child()");
		Child c = new Child();
		System.out.println("\n---- c.action()");
		c.action();
		Base b = c;
		System.out.println("\n---- b.action()");
		b.action();
		System.out.println("\n---- b.s：" + b.s);
		System.out.println("\n---- c.s：" + c.s);
	}
}

Memory layout as shown:

Second, the process of object creation

After the class is loaded, the process of creating an object, including:

1. Allocate memory;
2. Assign default values ​​for all instance variables;
3. Examples of code execution.

Each object instance variable is stored in addition to the class, the class also holds the actual information to be referred.
Examples are as follows:
Child Child new new C = (); Child objects will be newly created reference to a variable c, and Base b = c; b will also reference the Child object.
After creating and assigning memory layout:

reference variable c and b allocated on the stack, they point to the same heap Child objects. Child objects stored in the method area Child type of address, there is a Base instance variables and instance variables Child a.