the class variables initlization

一、Class variables are shared among all instances of a class and can be accessed even in the absence of any instance. These variables are associated with the class--not with instances of the class--so they are logically part of the class data in the method area. Before a Java VirtualMachine uses a class, it must allocate memory from the method area foreach non-final class variable declared in the class.
类变量 static：所有对象可以用，存贮在方法区,而且是第一类使用时，进行初始化。如果一个对象改变这个值，哪么所有对象都能用新改变的值。

类常量 static final：存在常量池中,每一类有一个常量池，如果谁想用别的类常量，只要复制到自己的常量池中。

  

二、例子 ：

package jvm.ex1;

public class Examplelc {
       //类变量初始化
static int width;
static  int heigh=(int)(Math.random()*2.0);
      // This is the static initializer静态初始化 
static {
width = 3 * (int) (Math.random() * 5.0);
}
    static void main(String[] args)
   {
  Examplelc test=new  Examplelc();  
  
   }
}

三、什么时候会执行初始化

    1、new 一个类

    2、子类继承父类，会对父类初始化

    3、直接调用 Examplelc.width。即调用类静态类变量

         直接调用 Examplelc.静态方法。即调用类静态类方法。    

四、以建立对象为例子：

       

类变量默认方法<clinit

    // The code for height's class variable initializer beginshere// Invoke Math.random(), which willpush

三、初始化默认<clinit 方法，JVM自己调用。

 All the class variable initializers and static initializers of a classare collected by the Java compiler and placed into one special method,theclass initialization method. In the Java class file, the classinitialization method is named "<clinit".
 1、Initialization of a class consists of two steps:
      1》Initializing the class's direct superclass (if any), if the direct superclass hasn't already
        been initialized:如果父类未初始化，则初始化父类
      2》Executing the class's class initialization method, if it has one

       执行类的初始化方法