【java单例模式】

单例模式：懒汉式

public class SingletonTest {
    public static void main(String[] args) {
        Order order1 = Order.getInstance();
        Order order2 = Order.getInstance();
        System.out.println(order1==order2);//true
    }

}
class Order{
    //1.私有化构造器
    private Order(){

    }
    //声明变量,没有初始化,此对象也声明为static
    private static Order instance = null;

    //声明一个public、static的返回当前类对象的方法
    public  static synchronized Order getInstance(){
        if (instance==null){
            instance = new Order();
        }
        return instance;
    }



}

单例模式：饿汉式

public class Singleton {
    public static void main(String[] args) {
        Bank Bank1 = Bank.getInstance();
        Bank Bank2 = Bank.getInstance();


    }
}
class Bank{
    //1.私有化类的构造器
    private Bank() {

    }
    //内部创建类的对象
    private static Bank instance = new Bank();//静态方法只能调静态结构，所以也必须为静态
    //提供公共的方法
    public static Bank getInstance(){
        return instance;

    }
}