单例模式

/**
 * 双重校验锁
 *      双重判断 + 锁
 * @author ghy
 * @version 1.0
 * @date 2022-05-27
 */
public class Singleton {
    private static Singleton instance = null;

    public static Singleton getInstance() {
        if(instance == null) {
            synchronized (Singleton.class) {
                if(instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }

    private Singleton() {}

}