💻Step 12: Packages – 7th hour + code

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💡Definition

– Group of similar types of classes, interfaces and subpackages.

💡Categories-

Comparing built-in and user-defined packages in Java:

FeatureBuilt-in PackagesUser-defined Packages
Provided byJava runtime environmentDeveloper
ContainsPre-defined classes, interfaces, and methodsClasses and interfaces defined by developer
ImportingAutomatically importedMust be explicitly imported using import keyword
Naming conventionFollows specific convention (e.g. java.util, java.io)Can be named by developer, as long as it is a valid Java identifier
PurposeProvide pre-defined functionalityOrganize and reuse developer’s own code

💡1- Built in packages

– also called as predefined packages in java
 i.e- java.lang, java.util, java.io etc

💡2- User defined packages

-also called as developer/user defined packages

[To use class of other package, we have 3 options to choose]

OptionSyntaxExample
Fully Qualified Namepackage.ClassName.methodName()java.util.ArrayList.add()
Import using Package.Class before Class Declarationimport Package.Class;import java.util.ArrayList;
Import Full Packageimport Package.*;import java.util.*;
Static Importimport static Package.Class.methodName;import static java.lang.Math.PI;

💡a- using fully qualified name
qlfdname
💡b- by importing package.class (recommended)
pck-clas

💡C- by importing full package*
pck-ful

Note– importing package doesn’t include subpackage

💡Static Import

used to import only static member of a class instead of class.
pck-sttc

 

Interview Questions —

  • How packages are related to access modifiers?
  • How many ways are available to import class of other packages?

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