一般来说都用eclipse自动化图形工具搞定,我用的是ubuntu,所以需要自己打包引入。
什么是包?
这是对java源代码的组织和管理的一种方式,比如:当操作系统某个目录的文件非常多的时候,我们一般建立子目录分类管理,java中的包跟文件目录的作用类似。
1,声明一个包,用package,放在文件的第一行,如:
package com.ghostwu.HelloWorld; public class HelloWorld{ public static void main( String[] args ){ System.out.println( "hello world" ); } }
当,源代码中声明了一个包的时候,在编译的时候,需要这样做:【javac -d . HelloWorld.java】, -d: 后面指定编译生成的class文件存放的目录,
这里面的点(.)指的是当前目录。
ghostwu@dev:~/java/data_struct/package$ ls com ghostwu.jar HelloWorld.java Student.java Test2.java Test.java ghostwu@dev:~/java/data_struct/package$ rm -rf com ghostwu.jar ghostwu@dev:~/java/data_struct/package$ ls HelloWorld.java Student.java Test2.java Test.java ghostwu@dev:~/java/data_struct/package$ javac -d . HelloWorld.java ghostwu@dev:~/java/data_struct/package$ ls com HelloWorld.java Student.java Test2.java Test.java ghostwu@dev:~/java/data_struct/package$ tree com com └── ghostwu └── HelloWorld └── HelloWorld.class 2 directories, 1 file
我们也可以换个路径,如:我把它编译到~/tmp目录下
ghostwu@dev:~/java/data_struct/package$ ls ~/tmp allpy.tar.gz ghostwu@dev:~/java/data_struct/package$ javac -d ~/tmp HelloWorld.java ghostwu@dev:~/java/data_struct/package$ ls ~/tmp allpy.tar.gz com ghostwu@dev:~/java/data_struct/package$ tree ~/tmp/com /home/ghostwu/tmp/com └── ghostwu └── HelloWorld └── HelloWorld.class 2 directories, 1 file
2,接下来,我们定义两个类,来使用包
ghostwu@dev:~/java/data_struct/package$ cat Student.java package com.ghostwu.Student; public class Student { public void say(){ System.out.println( "my name is ghostwu" ); } }
ghostwu@dev:~/java/data_struct/package$ cat Test.java package com.ghostwu.Test; public class Test { public static void main( String[] args ){ com.ghostwu.Student.Student stu = new com.ghostwu.Student.Student(); stu.say(); } }
在Test类中,如果需要使用Student类,需要使用 包名.类名( com.ghostwu.Student.Student )
ghostwu@dev:~/java/data_struct/package$ tree com com └── ghostwu └── HelloWorld └── HelloWorld.class 2 directories, 1 file ghostwu@dev:~/java/data_struct/package$ ls com HelloWorld.java Student.java Test2.java Test.java ghostwu@dev:~/java/data_struct/package$ javac -d . Student.java ghostwu@dev:~/java/data_struct/package$ javac Test.java ghostwu@dev:~/java/data_struct/package$ java Test Error: Could not find or load main class Test
在上面,编译使用的过程中,我们发现,直接执行java test报了一个错误。这是因为我们Test也有声明包( com.ghostwu.Test ),所以,我们应该这样执行:
ghostwu@dev:~/java/data_struct/package$ tree com com └── ghostwu ├── HelloWorld │ └── HelloWorld.class └── Student └── Student.class 3 directories, 2 files ghostwu@dev:~/java/data_struct/package$ javac -d . Test.java ghostwu@dev:~/java/data_struct/package$ java Test Error: Could not find or load main class Test ghostwu@dev:~/java/data_struct/package$ java com.ghostwu.Test.Test my name is ghostwu
执行格式:【java 包名+类名】
3,你可能已经发现了,这种方式非常麻烦,在使用包,每次实例化都要new xxx(包名) = xxx(包名) .... ,我们可以通过import关键字,引入包,就不需要每次加上包前缀了。
ghostwu@dev:~/java/data_struct/package$ cat Test2.java package com.ghostwu.Test2; import com.ghostwu.Student.Student; public class Test2 { public static void main( String[] args ){ Student stu = new Student(); stu.say(); } }
ghostwu@dev:~/java/data_struct/package$ tree com com └── ghostwu ├── HelloWorld │ └── HelloWorld.class ├── Student │ └── Student.class └── Test └── Test.class 4 directories, 3 files ghostwu@dev:~/java/data_struct/package$ javac -d . Test2.java ghostwu@dev:~/java/data_struct/package$ java Test2 Error: Could not find or load main class Test2 ghostwu@dev:~/java/data_struct/package$ java com.ghostwu.Test2.Test2 my name is ghostwu
4,把所有的class打包成一个jar文件,称之为jar包,比如,我们把当前目录下的所有class文件,打成一个jar包,可以给别人使用了
【jar cvf ghostwu.jar com】 把com目录下的所有文件 打包成一个jar文件, c:创建jar文件 v:生产详细信息 f:指定jar包的名称
ghostwu@dev:~/java/data_struct/package$ tree com com └── ghostwu ├── HelloWorld │ └── HelloWorld.class ├── Student │ └── Student.class ├── Test │ └── Test.class └── Test2 └── Test2.class 5 directories, 4 files ghostwu@dev:~/java/data_struct/package$ ls com HelloWorld.java Student.java Test2.java Test.class Test.java ghostwu@dev:~/java/data_struct/package$ jar cvf ghostwu.jar com added manifest adding: com/(in = 0) (out= 0)(stored 0%) adding: com/ghostwu/(in = 0) (out= 0)(stored 0%) adding: com/ghostwu/HelloWorld/(in = 0) (out= 0)(stored 0%) adding: com/ghostwu/HelloWorld/HelloWorld.class(in = 448) (out= 302)(deflated 32%) adding: com/ghostwu/Test2/(in = 0) (out= 0)(stored 0%) adding: com/ghostwu/Test2/Test2.class(in = 347) (out= 254)(deflated 26%) adding: com/ghostwu/Student/(in = 0) (out= 0)(stored 0%) adding: com/ghostwu/Student/Student.class(in = 420) (out= 293)(deflated 30%) adding: com/ghostwu/Test/(in = 0) (out= 0)(stored 0%) adding: com/ghostwu/Test/Test.class(in = 344) (out= 255)(deflated 25%) ghostwu@dev:~/java/data_struct/package$ ls com HelloWorld.java Test2.java Test.java ghostwu.jar Student.java Test.class
5,执行jar包的时候,发现报错了
ghostwu@dev:~/java/data_struct/package$ java -jar ghostwu.jar no main manifest attribute, in ghostwu.jar
我们需要在ghostwu.jar包中,配置一个入口类
再次执行,就可以了
ghostwu@dev:~/java/data_struct/package$ java -jar ghostwu.jar my name is ghostwu
6,解压jar包【jar -xvf ghostwu.jar 】
ghostwu@dev:~/java/data_struct/package$ ls com HelloWorld.java Test2.java Test.java ghostwu.jar Student.java Test.class ghostwu@dev:~/java/data_struct/package$ rm -rf com ghostwu@dev:~/java/data_struct/package$ ls ghostwu.jar HelloWorld.java Student.java Test2.java Test.class Test.java ghostwu@dev:~/java/data_struct/package$ jar -xvf ghostwu.jar created: META-INF/ inflated: META-INF/MANIFEST.MF created: com/ created: com/ghostwu/ created: com/ghostwu/HelloWorld/ inflated: com/ghostwu/HelloWorld/HelloWorld.class created: com/ghostwu/Test2/ inflated: com/ghostwu/Test2/Test2.class created: com/ghostwu/Student/ inflated: com/ghostwu/Student/Student.class created: com/ghostwu/Test/ inflated: com/ghostwu/Test/Test.class ghostwu@dev:~/java/data_struct/package$ ls com HelloWorld.java Student.java Test.class ghostwu.jar META-INF Test2.java Test.java ghostwu@dev:~/java/data_struct/package$ tree com com └── ghostwu ├── HelloWorld │ └── HelloWorld.class ├── Student │ └── Student.class ├── Test │ └── Test.class └── Test2 └── Test2.class 5 directories, 4 files