5-to those who love computer programming

Dear friends, this is the fifth story of "I can't learn JAVA, I can't eliminate my sorrow". Here I am not a general JAVA expert. I am a little student, I am a little girl, and I am a little girl. I don't know if it's a problem to everyone when I publish a strange discussion on the COM free forum? In any case, the long post will continue to be serialized before it is given a severe warning from the postmaster.
For the sake of 100% respect for netizens, all these posts are carefully prepared by myself. There is no link between the lines about other URLs, and there is no commercial taste. Please read them with peace of mind.
I learned JAVA for more than two years. I found myself familiar with JAVA in the first year. I felt that JAVA had changed in the second year. I haven't touched her in many places yet. Now, even worse, the more I learned, the more I learned, it's really "no JAVA, no worries ". Sign ~~ (I'm sighing !)
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Let's talk less and get down to the truth.
I posted some basic concepts about classes and objects. Now let's take a look at the class libraries.
I wonder if you have stayed in a manufacturing factory. In Shenzhen, there are many plastic products and hardware products. In these factories, there is a process for producing things that cannot be escaped-manufacturing of work models. After the work model is completed, it has become an example for other products to manufacture. It should be said that the "slot" is more accurate. The ratio of the worker mode to the JAVA class is better. Perhaps, the model made by the former is hard, tangible, give people a sense of sureness, while the JAVA model made by the latter (Classes) is soft, give people a feeling of being unrealistic. The so-called layman looks at the excitement, and the experts guard the way. The workers who make plastic and hardware models certainly do not understand the software models we create with JAVA. However, hard models and soft models are mostly the same in terms of management. The people who will manage the JAVA model will certainly manage the work model. In turn, it will not be true. This deserves the pride of our family of JAVA.
The more products the manufacturer makes, the longer the model is. Many products are similar in appearance. The models of Nokia 3210 and 8250 are basically the same except for the latter. Therefore, most products have a high probability of repeated use of work models. In order to quickly find this model for the next product development, it is a good way to store the model separately and sort it by name. Vivo, this is the model cabinet of the Nokia 3210 series. It is placed with the model of this series, and there are some model manuals and technical materials. There is a model cabinet of the Nokia 8250 series, which stores the model of the 8250 series, instructions and technical materials ...... All these work-model cabinets are stored in a house. For now, call them a work-model warehouse. For the factory, what is the purpose of this model warehouse?
All JAVA models, that is, all JAVA classes, are managed in the same way as described above. The longer you develop software using JAVA, the more classes you write. To borrow the classes you write next time, you have to be the same as above, for JAVA classes (forgive me for using two different meanings of a word in the same sentence), this class is specially used to create buttons, labels, text boxes, and so on, this category is dedicated to the development of database applications, and the other category is specialized in color adjustment ...... For each category, please give him a name. What is the name? In Java, Swing (AWT in childhood), SQL, Color ......, This is usually not the case of Swing, SQL, and Color categories ......, It's about the Swing package, SQL package, Color package ...... All these packages are stored in one place (that is, under a folder). It can be seen that this folder is a gold mine.