Java

Java

1. handling error

   • try-catch/finally statement
     • try: contains code to execute
     • catch: executes only if matching exception is thrown
     • finally: contains code cleanup
   • Throwable
     • unchecked: no handling error is required but can
     • checked: Should specify a block of code to execute when thrown
   • recommendations
     • go from specific to general exception
   • own exception
     • inherit from Exception class
   • propagation
     • methods
       • 2 ways
         • catch exception
         • document (throws clause)
     • up the call stack

2. Packages

   • group of relates types, use packages to avoid name conflicts, and to write a better maintainable code
   • categories
     • built-in
       • packages from the Java API
     • User-defined Packages
       • Java use a file system directory to store them
         • Class files organized in hierarchical folders
   • import
     • On demand: The whole package
     • Single type: Specific classes
       • Safier: avoid confusions when classes in different packages share name
   • Access boundary
     • Outside package
     • Inside package
   • Archive file
     • 1 single file which contains all class files and used to distribute our module
     • JAR
       • Can create using JDK (jar command line), Intellij, Maven
     • optionally includes a manifest

3. interface

   • defines a contract (no implementation)
   • may contains
     • methods
       • implicity abstract
       • static
         • defined behavior
         • can not be overriden
         • accessibility
           • through interface
           • inside interface
       • default
         • accessibility
           • through the instance of the implementing class
           • an instance should be created
         • can be overriden
     • contants
     • attibutes
       • final by default
         • can contain classes
       • public BD
   • can extends
     • interfaces only

4. Static

   • attibute
     • All instances access the same value
   • method
     • can access static field only
       • there is no need to instanciate the object to call them
   • import
     • specific method into other classes
   • Initialization blocks
     • at the top of the class definition, inside curly brakets
     • have to handle checked exception
   • class
     • may has
       • normal attributes
       • normal methods

5. Class

   • abstract
     • methods
       • can implement behavior
     • attributes
       • may be non-final
       • access modifiers: any
     • extend
       • classes
     • implement
       • multiple interfaces

6. Modifiers

   • final
     • keep the value constant
     • attibutes
     • references
       • allow to change the value of the pointed entity(String builder eg)
     • classes
       • not allowed to be extended
     • methods
       • doesn`t allow overring in extended classes

7. versions features

   • Java 8
     • lambda expressions
       • provides implementation of funcional interface
         • interface with only one abstract method
           • @FunctionalInterface notation
       • multiple arguments
       • useful with collections
     • method references

8. tricks

   • anonymous object
     • use a method without assigning it to any reference

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