Packages

Packages

It is an encapsulation mechanism to group related classes and interfaces into a single module. The main purpose of packages are

  • To resolve naming conflicts
  • To provide security to the classes and interfaces. So that outside person can’t access directly.
  • It improves modularity of the application.

There is one universally accepted convention to name packages i.e., to use internet domain name in reverse.

com.icicibank.loan.houseingloan.Account
package com.ashok.helloworld;

public class HelloWorld {
   public static void main(String[] args) {
      System.out.println("Hello World");
   }
}
javac HelloWorld.java
The generated class file will be placed in current working directory.

javac -d . HelloWorld.java
-d : Destination to place generated class files
.  : Current working directory

Generated class file will be placed into corresponding package structure.

  • If the specified package structure is not already available then this command itself will create that package structure.
  • As the destination we can use any valid directory

E.g

javac -d c: HelloWorld.java

If the specified destination is not available then we will get compilation error

E.g

javac -d z: HelloWorld.java

Here z: is not already available then we will get compile time error

Conclusions

In any java program there should be only at most 1 package statement. If we are taking more than one package statement we will get compile time error.

E.g

package pack1;
package pack2;
class A {

}
C.E: class, interface or enum expected

In any java program the first non comment statement should be package statement if it is available.

E.g

import java.util.*;
package com.ashok;
class A {

}
C.E: class, interface or enum expected

Packages


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