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Java- Interview


Here are some popular tips in Java

General Question

  • JVM - Java Virtual Machine. Used to execute byte code. Platform dependent (but byte code is platform independent)
  • JRE- Java Run time Environment. It provides run time environment and it's the implementation of JVM. It contains libraries and files that need to execute JVM.  
  • JDK- Java Development Kit. It contains JRE and development tools.
  • Why java doesn't support pointers: It's insecure and complex to understand
  • We can save java file with another name if class is not defined as public
  • Java use camalCase notation for objects naming (ex: firstName)

OOP Concepts Related 

  • Aggregation: weak relationship (bike has an indicator)
  • Composition:  strong relationship (bike has an engine)

GUI

  • Java GUI - Install Window builder to create GUI using Eclipse IDE

Code Related

  • No issues when you write static public void instead of public static void
  • We can execute program without main method : using static block 
  • this : refer the current object
  • Super class of every class : object class
  • Can't use both super() and this() in constructor at once
  • Can overload main method
  • Can declare main method as final
  • final class
    • can't inherit

Variables Related 

  • Local variables are not initialized to any default value
  • Static variables: 
    • used to refer the common property of all objects
  • final variables:
    • can't change the value

Method Related 

  • Constructor: It is a method that used to create objects
  • Return value of constructor : current instance
  • Constructor can't inherit and can't define as final
  • Static methods :
    • can invoke without initializing objects
    • can't override (Because they are part of the class, not the object)
  • final methods:
    • can't override
  • main method is static: because it's invoked before  initializing objects
  • If static keyword is removed from main method: program compiles but gives run time error




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