join() method of Thread class will wait the sub thread to finish then to continue the current thread. "join" looks like the sub-thread join the main thread. If you want to know the result of sub-thread, join can help you blocked the main thread until sub-thread finish(dead).
wait, notify and notifyAll are all method of Object. It means that every object in java can be a lock monitor. When you use synchronized you get the lock of object. Use synchronized on the method current thread will get the lock of instance. If you add synchronized on a static method that means current thread will get the lock of this Class. These 3 methods can not be used without synchronized (you can release the lock without geting it).
When you send GET request to server, you need to encode the data which contained in the url.In this way can make sure the data you send could be received by server correctly. Certainly, serve has to decode the data before using them. The example is like following.
Quicksort is one of the most common sorting algorithms. The logic of Quicksort is choosing a number (called pivot) and divide the rest into two parts. After first sorting the numbers on the left side are all less than pivot and the numbers on the right side are all bigger than pivot. Then do the same thing for left and right part.
The statement of creating index on table will lock the table.It will cost a long time if you create multiple indexes in a big table. You can use ALTER TABLE ... to create or drop multiple indexes in one sql. The example is here.
If the message No space left on device appears that means you need clear the file on your system or add new disk for your computer. "No space" not only means no free disk, it may also mean there is no iNodes in your system.
MyBatis is a Java persistence framework. It is easy to use and learn. This tutorial shows the most common scenarios.
The first level cache is enabled by default in MyBatis. It will cache the result after querying data from database. The second time you query MyBatis won't hit db. The first level cache is for session. If the session is close the cache will be cleared. I assume that you have created database and insert some data in your table.
In MySQL you can use desc to show the details of table. There is no desc command in PostgreSQL, but you can use \d or \d+ to show the table detail.
Swagger can help you generate document for your restful API. This blog will show you how to use it. I assume that you have known how to use Spring Boot. The structure of example project is like following.
Use jsonassert framework to compare two json are same or not. It only compare the content of them. The example code is here;
Use \d or \d+ in psql command to show all tables. \d+ will show additional detail of tables;
The annotation @ResponseBody can help you convert object to json. Sometimes if the field of object is null the json returned like following.
Use set command to list all environment variables. They are like following in my computer.
Use du command to show the size of folder. Before testing this command we will create a directory and a file.