Java有序性案例

/**
 * @author 晓果冻
 */
public class SingleInstance {
    
    private static SingleInstance instance;
    
    private SingleInstance(){};
    
    public static SingleInstance getInstance(){
        if(instance == null){
            synchronized (SingleInstance.class){
                if(instance == null){
                    instance = new SingleInstance();
                }
            }
        }
        return instance;
    }
}

instance = new SingleInstance();//这行代码包括如下三个步骤