Java How To Call Non Static Method From Main Method

Question

I m learning java and now i ve the following problem  I have the main method declared as  public static void main String   args               Inside my main method  because it is static I can call ONLY other static method    Why    For example  I have another class   public class ReportHandler               private Connection conn          private PreparedStatement prep       public void executeBatchInsert                 So in my main class I declare a private ReportHandler rh   new ReportHandler     But I can t call any method if they aren t static   Where does this go wrong   EDIT  sorry  my question is  how to  design  the app to allow me to call other class from my  starting point   the static void main

User · Answer

You can t call a non-static method from a static method  because the definition of  non-static  means something that is associated with an instance of the class   You don t have an instance of the class in a static context

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A static method means that you don t need to invoke the method on an instance  A non-static  instance  method requires that you invoke it on an instance  So think about it  if I have a method changeThisItemToTheColorBlue   and I try to run it from the main method  what instance would it change  It doesn t know  You can run an instance method on an instance  like someItem changeThisItemToTheColorBlue     More information at http   en wikipedia org wiki Method  computer programming  Static methods

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Please find answer   public class Customer        public static void main String   args            Customer customer new Customer            customer business               public void business            System out println  Hi Harry

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Since you want to call a non-static method from main  you just need to create an object of that class consisting non-static method and then you will be able to call the method using objectname methodname    But if you write the method as static then you won t need to create object and you will be able to call the method using methodname    from main  And this will be more efficient as it will take less memory than the object created without static method

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You cannot call a non-static method from the main without instance creation  whereas you can simply call a static method  The main logic behind this is that  whenever you execute a  class file all the static data gets stored in the RAM and however  JVM java virtual machine  would be creating context of the mentioned class which contains all the static data of the class   Therefore  it is easy to access the static data from the class without instance creation The object contains the non-static data Context is created only once  whereas object can be created any number of times  context contains methods  variables etc  Whereas  object contains only data  thus  the an object can access both static and non-static data from the context of the class

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You can think of a static member function as one that exists without the need for an object to exist   For example  the Integer parseInt   method from the Integer class is static   When you need to use it  you don t need to create a new Integer object  you simply call it   The same thing for main     If you need to call a non-static member from it  simply put your main code in a class and then from main create a new object of your newly created class

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Useful link to understand static keyword https   www codeguru com java tij tij0037 shtml Heading79

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Java is a kind of object-oriented programming  not a procedure programming  So every thing in your code should be manipulating an object   public static void main is only the entry of your program  It does not involve any object behind   So what is coding with an object  It is simple  you need to create a particular object instance  call their methods to change their states  or do other specific function within that object   e g  just like  private ReportHandler rh   new ReportHandler    rh  lt function declare in your Report Handler class gt    So when you declare a static method  it doesn t associate with your object instance of your object  And it is also violate with your O-O programming    static method is usually be called when that function is not related to any object behind

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You simply need to create an instance of ReportHandler   ReportHandler rh   new ReportHandler    constructor args here      rh executeBatchInsert       Having fixed name to follow conventions   The important point of instance methods is that they re meant to be specific to a particular instance of the class    so you ll need to create an instance first  That way the instance will have access to the right connection and prepared statement in your case  Just calling ReportHandler executeBatchInsert  there isn t enough context   It s really important that you understand that    Instance methods  and fields etc  relate to a particular instance Static methods and fields relate to the type itself  not a particular instance   Once you understand that fundamental difference  it makes sense that you can t call an instance method without creating an instance    For example  it makes sense to ask   What is the height of that person    for a specific person  but it doesn t make sense to ask   What is the height of Person    without specifying a person    Assuming you re leaning Java from a book or tutorial  you should read up on more examples of static and non-static methods etc - it s a vital distinction to understand  and you ll have all kinds of problems until you ve understood it

[java] Java: How To Call Non Static Method From Main Method?

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