What do you need to know to get started with Java? In fact, you don’t need to know a lot. As long as you study hard, you can learn everything well.
Now I have started my career of learning Java: [The Jdk version I downloaded is jdk-8u5-windows-x64]
1. Directory after installation:
->Source Code: Installing this option will install the source code of all core Java class libraries
->bin: Various tool commands of the JDK are stored in this path, such as commonly used Javac, java Wait for orders.
->db: This path is the path to install Java DB [DB (data base, database) is a collection of data organized according to a certain data model and stored in secondary storage. 】
->include: Some platform-specific header files.
->jre: Installed in this path is the JRE environment required to run Java programs.
->lib: This path stores the actual execution program of the JDK tool command. (It contains what is needed for compilation and operation: dt.jar and tools.jar)
->javafx-src.zip: This compressed file stores the source code of all core class libraries of Java FX.
->src.zip: This compressed file stores the source code of all core Java class libraries.
-> Descriptive documents such as README and LICENSE.
2. Regarding the setting of environment variables:
->Path=D:\Java\jdk1.8.0_05\bin (the location of the JDK installation->The location of the JDK tool)
->CLASSPATH: In versions above JDK 1.5, there is no need to set it separately. Of course, there is no error if the setting is made, but it should be noted that adding (.) represents the current directory.
【General setting is: D:\Java\jdk1.8.0_05\bin\dt.jar;.;D:\Java\jdk1.8.0_05\bin\tools.jar 】
3.Java source file naming rules and case issues
->Class name.java, regarding the class name, if the public modifier is not used in the file, then any name that conforms to the rules can be used, but if If a public class is defined in the source file, then it must have the same name as the defined class; only one public class can be defined in the source file at most.
->Java is strictly case-sensitive: Java keywords are all lowercase, no capital letters are required.
->main: The compiled class must have main in it if it needs to run. This main method must be modified with public and static.
It must be void. Declare the return value of the method, and the parameter type can only be a string array, not other forms of parameters. In addition, the public and static positions can be interchanged,
but the other positions are fixed.
-> eg: public static void main(String[] args)
4. Java’s garbage collection mechanism
The memory allocation and recycling of Java programs are all performed by JRE does this automatically in the background. JRE will reclaim memory spaces that are no longer in use. These memory spaces are memory spaces in the JVM heap memory.
Garbage collection is a dynamic storage management technology that automatically releases objects that are no longer referenced by the program and implements the automatic recycling function of memory resources according to a specific garbage collection algorithm.
Of course, garbage collection cannot be precisely controlled, which means that it will be executed automatically when the CPU is idle or the memory is about to be exhausted.
The current JVM has a variety of garbage collection mechanisms.
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