为 static 变量分配空间，设置默认值（准备阶段）

话不多说直接上代码：

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

package com.beyond.dhl;     class Singleton {     private static Singleton instance;   // 懒汉式所以不会进行实例化对象       private Singleton() {         System.out.println("构造方法:" + Thread.currentThread().getName());     }       public static Singleton getInstance() {         if (instance == null) {             instance = new Singleton();         }         return instance;     }     }   public class Test {     public static void main(String[] args) {         new Thread(() -> Singleton.getInstance(), "线程A").start();         new Thread(() -> Singleton.getInstance(), "线程B").start();         new Thread(() -> Singleton.getInstance(), "线程C").start();         new Thread(() -> Singleton.getInstance(), "线程D").start();         new Thread(() -> Singleton.getInstance(), "线程E").start();     } }

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

public class Demo01 {     public static void main(String[] args) {         int i = 10;  //十进制         int i2 = 010;  //八进制0         int i3 = 0x10;  //十六进制0x         int i4 = 0b10;  //二进制0b           System.out.println(i);         System.out.println(i2);         System.out.println(i3);         System.out.println(i4);     } }     public class Demo02 {     public static void main(String[] args) {         float f = 0.1f;         double d = 1.0/10;           System.out.println(f == d);         System.out.println(f);         System.out.println(d);           System.out.println("========================================");           float d1 = 233333333333333333F;         float d2 = d1 + 1;         System.out.println(d1 == d2);     } }   public class MyClass {     static int num; } public class Test_MyClass {     public static void main(String[] args) {         //可直接通过  类名.属性名  进行访问         MyClass.num=10;                   MyClass m1 = new MyClass();         m1.num=20;         System.out.println(m1.num);//num=20                   MyClass m2 = new MyClass();         m2.num=30;         System.out.println(m2.num);//num=30         System.out.println(m1.num);//num=30     } }     package com.soder; public class Soder1 extends Soders{           public Soder1() {         p--;         System.out.println("子类构造方法\t"+p);     }     {         System.out.println("子类代码块\t"+p);     }           static {         System.out.println("子类静态代码块\t"+p);     }     public static void m1() {         System.out.println("子类静态指令m1\t"+p);     }     public void m2() {         System.out.println("子类指令m2\t"+p);     } }

tips：当类被加载时，类的所有信息（包名，类名，属性，方法等）都会被加载到方法区，而其中的静态属性方法又会被调进静态域，可通过类名直接调用出来