• The subpackage is a package within a package.
• It should be developed to further categorize the package.
• Sub packages are identical to packages, with the exception that they are defined within other packages.
• Sub packages are similar to subdirectories, which are directories within directories.
• Sub packages in themselves are packages, so you have to use/access them similar to packages.
• They can also contain any types, such as classes, interfaces, and enums.

Example:

package com.coderzpy.code;  
class Simple{  
  public static void main(String args[]){  
   System.out.println("Hello subpackage");  
  }  
}  

To Compile: javac -d . Simple.java

To Run: java com.coderzpy.code.Simple

Output

Hello subpackage

Why do we make Sub Packages in the first place?

Sub packages are used to further categorize and divide a package. It’s comparable to creating a subfolder within a folder to further categorize it so you can better organize your stuff and make it easier to access. A package may contain several sub-packages.

Example of Predefined SubPackage in Java:

The Pattern class of the java.util.regex subpackage is demonstrated in the sample below. Regular expression classes and interfaces are contained in this sub package.

 import java.util.regex.Pattern;
 // To imports all classes of java.util.regex subpackage.
 // import java.util.regex.*; 
 
 class Pattern_program {
   public static void main(String args[]) { 
      // Checks if the given string contains only alphabets
      System.out.println(Pattern.matches("[a-zA-Z]*", "JavaCoding"));
      System.out.println(Pattern.matches("[a-zA-Z]*", "JavaCoding2Coderzpy"));
      // Checks if the given string contains only numbers
      System.out.println(Pattern.matches("[0-9]*", "123456"));
      System.out.println(Pattern.matches("[0-9]*", "123XZY6"));     
   }
 }

Output:

true
false
true
false

Java Static Import:

Java 5’s static import feature allows java programmers to directly access any static member of a class. It’s not necessary to qualify it with the class name.

Note:

• Static import has the advantage of requiring less coding if you frequently access any static member of a class.
• Static import’s disadvantage is that it renders your program illegible and unmaintainable if you use it too much.

Example:

import static java.lang.System.*;    
class StaticImportExample{  
  public static void main(String args[]){  
     
   out.println("Hello");//Now no need of System.out  
   out.println("Java");  
  
 }   
}      

Output:

Hello
Java

Note: also read about the Packages in Java

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