单例模式懒汉式

单例模式
懒汉式：用的时候才创建对象

public class Teacher {
    private  Teacher(){}

    private static Teacher t=null;

    //调用方法的时候再new Teacher();
    //懒汉式有线程安全问题
    //要加synchronized
    public synchronized static Teacher GetTeacher(){
        //t等于null就new
        //这里如果有多个线程就会出问题
        if(t==null){
            t=new Teacher();
        }
        return t;
    }
}

public class TeacherDemo {
    public static void main(String[] args) {
        Teacher t1=Teacher.GetTeacher();
        Teacher t2=Teacher.GetTeacher();
        System.out.println(t1==t2);

    }
}