super in Java

Question

Is super   used to call the parent constructor  Please explain super

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Yes  super    lowercase  calls a constructor of the parent class  You can include arguments  super foo  bar   There is also a super keyword  that you can use in methods to invoke a method of the superclass  A quick google for  Java super  results in this

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super   calls the parent constructor with no arguments   It can be used also with arguments  I e  super argument1  and it will call the constructor that accepts 1 parameter of the type of argument1  if exists    Also it can be used to call methods from the parent  I e  super aMethod    More info and tutorial here

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Is super   is used to call the parent constructor     Yes       Pls explain about Super      super   is a special use of the super keyword where you call a parameterless parent constructor  In general  the super keyword can be used to call overridden methods  access hidden fields or invoke a superclass s constructor   Here s the official tutorial

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Source article  Java  Calling super      Yes  super      will invoke the constructor of the super-class   Illustration     Stand alone example   class Animal       public Animal String arg            System out println  Constructing an animal      arg            class Dog extends Animal       public Dog             super  From Dog constructor            System out println  Constructing a dog              public class Test       public static void main String   a            new Dog              Prints   Constructing an animal  From Dog constructor Constructing a dog

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Some facts    super   is used to call the immediate parent  super   can be used with instance members   i e   instance variables and instance methods  super   can be used within a constructor to call the constructor of the parent class    OK  now let   s practically implement these points of super     Check out the difference between program 1 and 2  Here  program 2 proofs our first statement of super   in Java   Program 1  class Base       int a   100     class Sup1 extends Base       int a   200      void Show                 System out println a           System out println a             public static void main String   args                new Sup1   Show              Output      200   200   Now check out program 2 and try to figure out the main difference   Program 2  class Base       int a   100     class Sup2 extends Base       int a   200      void Show                 System out println super a           System out println a             public static void main String   args                new Sup2   Show              Output      100   200   In program 1  the output was only of the derived class  It couldn t print the variable of neither the base class nor the parent class  But in program 2  we used super   with variable a while printing its output  and instead of printing the value of variable a of the derived class  it printed the value of variable a of the base class  So it proves that super   is used to call the immediate parent   OK  now check out the difference between program 3 and program 4   Program 3  class Base       int a   100      void Show                 System out println a            class Sup3 extends Base       int a   200      void Show                 System out println a             public static void Main String   args                new Sup3   Show              Output      200   Here the output is 200  When we called Show    the Show   function of the derived class was called  But what should we do if we want to call the Show   function of the parent class  Check out program 4 for the solution   Program 4  class Base       int a   100      void Show                 System out println a            class Sup4 extends Base       int a   200      void Show                 super Show            System out println a             public static void Main String   args                new Sup4   Show              Output      100   200   Here we are getting two outputs  100 and 200  When the Show   function of the derived class is invoked  it first calls the Show   function of the parent class  because inside the Show   function of the derived class  we called the Show   function of the parent class by putting the super keyword before the function name

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super is a keyword  It is used inside a sub-class method definition to call a method defined in the superclass  Private methods of the superclass cannot be called  Only public and protected methods can be called by the super keyword  It is also used by class constructors to invoke constructors of its parent class   Check here for further explanation

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For example  in selenium automation  you have a PageObject which can use its parent s constructor like this   public class DeveloperSteps extends ScenarioSteps    public DeveloperSteps Pages pages        super pages

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Constructors In a constructor  you can use it without a dot to call another constructor  super calls a constructor in the superclass  this calls a constructor in this class nbsp    public MyClass int a      this a  5       Here  I call another one of this class s constructors     public MyClass int a  int b      super a  b       Then  I call one of the superclass s constructors      super is useful if the superclass needs to initialize itself  this is useful to allow you to write all the hard initialization code only once in one of the constructors and to call it from all the other  much easier-to-write constructors   Methods In any method  you can use it with a dot to call another method  super method   calls a method in the superclass  this method   calls a method in this class nbsp    public String toString       int    hp     this hitpoints        Calls the hitpoints method in this class                                         for this object    String name   super name            Calls the name method in the superclass                                         for this object     return       name          hp     HP        super is useful in a certain scenario  if your class has the same method as your superclass  Java will assume you want the one in your class  super allows you to ask for the superclass s method instead  this is useful only as a way to make your code more readable

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As stated  inside the default constructor there is an implicit super   called on the first line of the constructor   This super   automatically calls a chain of constructors starting at the top of the class hierarchy and moves down the hierarchy    If there were more than two classes in the class hierarchy of the program  the top class default constructor would get called first   Here is an example of this   class A       A         System out println  Constructor A             class B extends A       public B         System out println  Constructor B             class C extends B        public C         System out println  Constructor C               public static void main String   args        C c1   new C               The above would output   Constructor A Constructor B Constructor C

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I would like to share with codes whatever I understood   The super keyword in java is a reference variable that is used to refer parent class objects  It is majorly used in the following contexts -  1  Use of super with variables   class Vehicle         int maxSpeed   120          sub class Car extending vehicle    class Car extends Vehicle         int maxSpeed   180        void display                      print maxSpeed of base class  vehicle             System out println  Maximum Speed      super maxSpeed                  Driver program to test    class Test         public static void main String   args                  Car small   new Car             small display                 Output -  Maximum Speed  120    Use of super with methods       Base class Person    class Person         void message                   System out println  This is person class                   Subclass Student    class Student extends Person         void message                   System out println  This is student class                    Note that display   is only in Student class      void display                      will invoke or call current class message   method          message                 will invoke or call parent class message   method          super message                   Driver program to test    class Test         public static void main String args                    Student s   new Student                 calling display   of Student          s display                Output -  This is student class This is person class   3  Use of super with constructors   class Person         Person                   System out println  Person class Constructor                   subclass Student extending the Person class    class Student extends Person         Student                      invoke or call parent class constructor          super              System out println  Student class Constructor                   Driver program to test   class Test         public static void main String   args                  Student s   new Student                 Output -  Person class Constructor Student class Constructor

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I have seen all the answers  But everyone forgot to mention one very important point   super   should be called or used in the first line of the constructor

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The super keyword can be used to call the superclass constructor and to refer to a member of the superclass  When you call super   with the right arguments  we actually call the constructor Box  which initializes variables width  height and depth  referred to it by using the values of the corresponding parameters  You only remains to initialize its value added weight  If necessary  you can do now class variables Box as private  Put down in the fields of the Box class private modifier and make sure that you can access them without any problems   At the superclass can be several overloaded versions constructors  so you can call the method super   with different parameters  The program will perform the constructor that matches the specified arguments   public class Box        int width      int height      int depth       Box int w  int h  int d            width   w          height   h          depth   d             public static void main String   args           HeavyBox heavy   new HeavyBox 12  32  23  13             class HeavyBox extends Box        int weight       HeavyBox int w  int h  int d  int m               call the superclass constructor         super w  h  d           weight   m

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That is correct  Super is used to call the parent constructor  So suppose you have a code block like so  class A      int n      public A int x           n   x           class B extends A      int m      public B int x  int y           super x           m   y            Then you can assign a value to the member variable n

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Calling the no-arguments super constructor is just a waste of screen space and programmer time  The compiler generates exactly the same code  whether you write it or not   class Explicit         Explicit             super             class Implicit       Implicit

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Just super    alone will call the default constructor  if it exists of a class s superclass  But you must explicitly write the default constructor yourself  If you don t a Java will generate one for you with no implementations  save super      referring to the universal Superclass Object  and you can t call it in a subclass   public class Alien     public Alien      Default constructor is written out by user        Implementation not shown               public class WeirdAlien extends Alien     public WeirdAlien       super      calls the default constructor in Alien

[java] super() in Java

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