Chapter One Java language Overview and development environment

JRE: Runtime environment, including core API, integration API, user interface API, release technology, Java Virtual Machine (JVM)

JDK: Development environment, including compiler for compiling Java programs (i.e. Javac command)

After the Java program compiles the steps to generate the bytecode (*.class file), the bytecode needs to be interpreted using the Java interpreter. The JVM that executes the bytecode file.

JDK Installation Setup issues:

Set the PATH environment variable: Windows looks for the command to execute under the path in the paths environment and determines whether the current command can be executed, depending on whether it is found. (JDK installation path. bin is the value in the environment variable)

　　

If my path is generally: D:\extral\java_jdk\32jdk\bin. In general, it is best not to have Chinese and white space in the path (this problem should be noted for most software)

Set CLASSPATH environment variable: You only need to set the value of Classpath when using an earlier version of the JDK, or you can set the CLASSPATH environment variable for more than 1.5.

Compile and execute the Java class in the Dt.jar Tools.jar file under the Lib file under the JDK installation path, so add both to the classpath.

Note: Add "." to the front of the path. Indicates that the Java class is searched under the current path.

Garbage collection mechanism:

Memory leaks: If some of the allocated memory is not recycled, it can cause the system to run down or even become paralyzed.

Java JVM uses garbage collection algorithm to recycle garbage automatically: 1. Find useless objects; 2. Reclaim memory space occupied by useless objects, which is the space that can be reused by the program.

Book author to beginners Java advice: Do not use any of the IDE, only when we fully understand the IDE in the back of the operation of the mechanism behind each button to use it. If a programmer is connected to a basic

The "1 + 1" problem requires tools, so the consequences can be imagined.

Modify your own editor options to make them easy to use.

　　UE : It took a long time to finally succeed. Here's the principle, right.

　　

　　Sentiment: When a thing you have not touched, the best way is to understand the help document, which helps you understand the actual meaning of each parameter. and the online tutorial you can refer to, if there is time to understand how he will succeed, and each command or practice behind what happened. (This is my biggest harvest today!) ）

　　

DOS Command (Advanced menu)

This command is used to run DOS commands from inside the UltraEdit and capture command execution results, which are automatically displayed with UltraEdit after the command is completed.

C:\comp\compiler%F

when this command executes,%F is replaced with the full path, file name, and extension of the file in the active window, which is saved before the command executes.  

The following commands can be passed as part of the full file name:

%P path Only ("C:\project\test\")

%N file name only ("test")

%E only extension (". C")  

%p%n%e equals%F, which is the above example ("C:\project\test\test.c").  

Note-if%f,%p,%n,%e are lowercase letters, the filenames are passed with a long file name and should be enclosed in quotation marks, such as "%f" or "%p%n". If%F,%P,%N, and%E are uppercase letters, the file name and path passed will be converted to the "8.3" short file name format for maximum compatibility with DOS programs.

In addition, the following commands are available:

%R can be used for the full path/name of the scheme (%R indicates a long file name, and% R denotes short file name)

%RP can be used for the full scheme path (%RP represents a long file name,%RP represents a short file name)

%rn only for scheme names (%rn denotes long filenames,%rn denotes short filenames)

%modify% In some cases, you might need to modify the command-line arguments every time the tool runs. To make modifications and add%modify% to the command line, a dialog box is displayed when the tool is run, and the user can modify the command line or cancel the run without modification.

%sel% This is used to let UltraEdit add the highlighted/selected text from the active document to the command line, replacing the%sel% parameter.

%env: Allows the user to use environment variables in the command. The environment variables follow directly in%env: Later, UltraEdit is replaced with the contents of the matching environment variable.

%line% This is used to let UltraEdit add the line number where the cursor is to the command line, replacing%line%-1 for the first row.

%col% This is used to let UltraEdit add the column number where the cursor is to the command line, replacing%col%-1 to indicate the first column.  

Chapter One Java language Overview and development environment