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：

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();    }}

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=20MyClass m2 = new MyClass();m2.num=30;System.out.println(m2.num);//num=30System.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