calling another method from the main method in java [duplicate]

Answer 1

You can do it multiple ways. Here are two. Cheers!

package learningjava;

public class helloworld {
    public static void main(String[] args) {
        new helloworld().go();
        // OR
        helloworld.get();
    }

    public void go(){
        System.out.println("Hello World");
    }
    public static void get(){
        System.out.println("Hello World, Again");
    }
}

Answer 2

First java will not allow you to have do() method. Instead you can make it doOperation().

Second You cann't invoke directly non static methods from static function. Main is a static function. You need to instantiate the class first and then invoke method using that instance.

Third you can invoke static method directly from non static methods.

Answer 3

Check out for the static before the main method, this declares the method as a class method, which means it needs no instance to be called. So as you are going to call a non static method, Java complains because you are trying to call a so called "instance method", which, of course needs an instance first ;)

If you want a better understanding about classes and instances, create a new class with instance and class methods, create a object in your main loop and call the methods!

 class Foo{

    public static void main(String[] args){
       Bar myInstance = new Bar();
       myInstance.do(); // works!
       Bar.do(); // doesn't work!

       Bar.doSomethingStatic(); // works!
    }
 }

class Bar{

   public do() {
   // do something
   }

   public static doSomethingStatic(){
   }
}

Also remember, classes in Java should start with an uppercase letter.

Answer 4

You can only call instance method like do() (which is an illegal method name, incidentally) against an instance of the class:

public static void main(String[] args){
  new Foo().doSomething();
}

public void doSomething(){}

Alternatively, make doSomething() static as well, if that works for your design.

Answer 5

If you want to use do() in your main method there are 2 choices because one is static but other (do()) not

1. Create new instance and invoke do() like new Foo().do();
2. make static do() method

Have a look at this sun tutorial

Answer 6

This is a fundamental understanding in Java, but can be a little tricky to new programmers. Do a little research on the difference between a static and instance method. The basic difference is the instance method do() is only accessible to a instance of the class foo.

You must instantiate (create an instance of) the class, creating an object, that you use to call the instance method.

I have included your example with a couple comments and example.

public class SomeName {

//this is a static method and cannot call an instance method without a object
public static void main(String[] args){

    // can't do this from this static method, no object reference
    // someMethod();

    //create instance of object
    SomeName thisObj = new SomeName();
    //call instance method using object
    thisObj.someMethod();
}

//instance method
public void someMethod(){
    System.out.print("some message...");
}

}// end class SomeName