Java Package Tutorial (English version) - The Diigo Meta page

• 16 Jul 17
  

  Rita Zerrizuela

  • Our CLASSPATH then needs to be changed to point to the new location of the package world accordingly. 

    set CLASSPATH=.;C:\myclasses; 

     Thus, Java will look for java classes from the current directory and C:\myclasses directory instead. 

    Someone may ask "Do we have to run the HelloWorld at the directory that we store its class file everytime?". The answer is NO. We can run the HelloWorld  from anywhere as long as we still include the package world in the CLASSPATH.

  • How to use package

     There are 2 ways in order to use the public classes stored in package. 
    1. Declare the fully-qualified class name. For example, 

    ... world.HelloWorld helloWorld = new world.HelloWorld(); world.moon.HelloMoon helloMoon = new world.moon.HelloMoon(); String holeName = helloMoon.getHoleName(); ... 

     2) Use an "import" keyword: 

    import world.*;  // we can call any public classes inside the world package  import world.moon.*;  // we can call any public classes inside the world.moon package import java.util.*;  // import all public classes from java.util package import java.util.Hashtable;  // import only Hashtable class (not all classes in java.util package) 

     
  • Note that if the package is stored inside a jar file, we have to include the jar file with its extension (.jar)  in the CLASSPATH. However, if the package is a plain directory, we just put the name of directory into the CLASSPATH.

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  • C:\world>java world.HelloWorld
  • fully-qualified class name is the name of the java class that includes its package name
  • set CLASSPATH=.;C:\myclasses;
  • import world.*; // we can call any public classes inside the world package  import world.moon.*; // we can call any public classes inside the world.moon package import java.util.*; // import all public classes from java.util package import java.util.Hashtable; // import only Hashtable class (not all classes in java.util package)
  • Normally, we can see what is inside  a jar file by using the command jar -tvf fileName.jar
  • Note that if the package is stored inside a jar file, we have to include the jar file with its extension (.jar)  in the CLASSPATH. However, if the package is a plain directory, we just put the name of directory into the CLASSPATH.

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