For beginners 2: Start With JDK

For beginners 2: Start With JDK

After learning about the advantages and capabilities of Java

Let's talk about how to learn Java.

 

Before talking about how to learn Java, it is necessary to give a brief description of several major directions of Java.

Five years ago, well, it was six years ago, that was 99 years ago.

Sun made a decision to divide the Java application platform

After all, language application features are different in different fields.

Sun can publish high-end standards to standardize code for applications in different fields

The three major blocks are j2se, J2EE, and

This action is definitely amazing today.

It is precisely because of this revolutionary development that Java is playing games in a small way.

Developing into the foundation of today's enterprise-level applications

 

Here, I would like to explain the meaning of 2 in j2se J2EE

Actually, 2 is the homophonic of the English word to, which means.

Instead of second edition, of course, Java 2 itself is 1.2, which is also a bit 2nd Edition

 

The Java version released by sun is very interesting.

Although it is always written as 1.x, the external saying about this version is x.0.

For example, Java 2 is actually Java 1.2.

1.3 is actually 3.0, 1.4 is 4.0, and now 5.0 is actually 1.5

We used to call it 1.x.

Maybe after 5.0, it's all changed to x.0 instead of 1. X.

So don't be surprised to hear other people say that Java 5.0 is actually 1.5.

 

Among the three J2 * E, j2se is the foundation, that is, Java 2 Standard Edition (Java 2 Standard Edition)

That is, the most basic Java language. No matter what Java technology you learn, j2se must be mastered.

To use j2se, you must install JDK (Java Development Kit)

JDK can be downloaded for free on Sun's homepage. You need to install JDK after the download. For the installation process, refer to the teaching materials.

JDK includes five parts: core API, integrated API, user interface API, publishing technology, and Java Virtual Machine (JVM)

 

First, let's talk about the runtime environment. The most important thing about the runtime environment is the Java Virtual Machine (JVM)

As we mentioned earlier, Java is a cross-platform language. How can we achieve cross-platform? After all, each operating system is different.

Java designers have proposed the concept of a virtual machine.

Establish a unified platform on the Operating System. This platform must implement certain functions to support program running.

For example:

-------------------------------------

| Program |

-------------------------------------

| JVM |

-------------------------------------

| UNIX | Windows | Linux | Solaris | ..

-------------------------------------

Every program written by a programmer runs on a virtual machine first.

All operations must pass through the Virtual Machine to interact with the operating system

This not only unifies all operating systems, but also ensures the security of the operating system.

The Virtual Machine (JVM) is dead and the operating system is not affected.

The Java Runtime Environment we call mainly refers to JVM, and the others are omitted.

 

The following describes the JDK (Java Development Kit) APIs. In fact, JDK is used to include the runtime environment and development tools.

I personally think it is inappropriate, because these three words can only describe the development tools, that is, several standard APIs.

There is no such thing as a running environment.

So what is API?

Simply put, it is the application programming interface and the application programming interface.

In Java, some written classes are packaged.

This also explains what is a class and what is a package. To put it simply, a package is a set of classes.

A package contains zero or multiple classes. Well, you can read the book.

These classes are the basic classes of Java. Common classes can be simply understood as Java tool sets.

 

Finally, let's talk about the Release Technology of JDK. In fact, according to my understanding, it's just the compiler.

A technique used to convert. java files to. class files.

These three parts constitute JDK. With JDK, you can develop j2se application software.

You only need to write a few lines of code using a notepad.

But in general, we will use development tools with better results, that is, IDE

Jcreator IDE is recommended in j2se.

Sun's products are seamlessly integrated with JDK, which is very suitable for beginners.

 

In terms of teaching materials, we recommend reading a copy of the Java tutorial published by the e-Industry Publishing House for both beginners and advanced articles.

Some people say that the 21-day series is a bad book, but I personally think

For j2se, this book has been translated very well, and there are basically no syntax errors, and the statements are fluent.

Thinking in Java

This book is naturally classic and detailed, but I don't think it is very suitable for beginners.

This is not a problem for beginners, but I personally think it is better to find this teaching material, that is, the two recommended ones.

The understanding of basic concepts is still based on teaching materials. After all, thinking in Java has poor translations.

In addition, I suggest reading the original version is better. Of course these books are the best, but if you don't have time

Read at least one of them, and then read the other two. In fact, the content of the three books is similar.

However, there are different ways of looking at the problem and the target readers. Well, what should I do? Find the one that suits me?

The last thing I want to talk about is:

Because of the existence of virtual machines, most j2se software is slower than general desktop software.

The effect is not satisfactory. Currently, only the swing control is still in use.

 

J2EE

This is the top priority of Java applications. If you want to earn a high salary, you 'd better learn J2EE well.

I remember seeing a survey on csdn in the past, where do tens of thousands of programmers earn a monthly salary?

Eight out of ten are for J2EE, the other two are for j2_based architecture, and the other one is for Embedded architecture.

It may be exaggerated, but it also shows the scarcity of J2EE talents and the wide application.

Therefore, if you want to learn Java, it is always not enough to be proficient in j2se. At least you need to know the other two J2 * E