How to compile java into class file

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1. Overview

General generation compiles java into class files, which can be written as follows:

a)。 Javac [- cp xxx.jar] xxxx.java

b)。 Javac [- cp xxx.jar]-d. Xxxx.java

c)。 Javac [- cp xxx.jar]-d. / classes xxxx.java

First, the second way is to generate the class file in the current directory, and the third way is to generate the class file under the classes folder

Depending on whether there is a package name package in the xxx.java file, the path of the class file generated by the first and the two methods is also different, which is illustrated by an example:

The demo.java file is as follows (no package name package):

Public class demo {public static void main (String [] args) {System.out.println ("hello world!");}} 2. No package explanation

The first way to run the result:

The second way to run the result:

The third way to run the result:

3. When there is a package name

There is a package name in demo.java:

Package cj.test;public class demo {public static void main (String [] args) {System.out.println ("hello world!");}}

The first method cannot be executed after compilation:

The second way:

The third way:

4. Third-party jar

If you use a third-party jar package when compiling (the java file has the package name package, the third-party jar used is placed in the jar folder, and the compiled file is placed in classes):

That is:

Javac-cp compilation using jar file-d compiled class location xxx.java

Java-cp executes the class location; executes the third-party jar compiled class file used (including package name)

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