家人们可以看看这句话怎么写代码吗

//[代码2]声明一个公有的静态的成员丽数getInstance,方法判断instance//成员变量是否为空，如果为空，则根据构造函数新建一个对象，否则返回instance

public class DoubleLock {

private volatile static DoubleLock instance;

private DoubleLock(){}

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

}