some queries

[Feng]

I got 3 questions regarding this:

Code:

public static void main (String [] args) {

a) there are many times that in order to run a program, we have to type String [] args. Why we use this? And why some times we dont need to type it? What does it mean?

b)why in some programs we type run instead of main?

c)when do we type static? only at the main method of our main class?

[staykovmarin]

String args[] are the arguments that you pass to the program:

Code:

java Prog args args1 args2

args are then the arguments, put in the args[] array like so

Code:

args[0] = args 
args[1] = args1
args[2] = args2

run() is only used in threads, if i am understanding you right.

static has a meaning too long to explain in a single post. You might want to read the java tutorials or get yourself a good book.

edit: you always need to have a main method. It is the entry point to your program. The class that has your main method is the class that you do

Code:

java Foo

and it run. Otherwise you get an error.

[Feng]

i dont put any args, at least up to now. but i have many times to write this String [] args in order not to have problems.

[Feng]

any answer plz?

[staykovmarin]

Thats because you are required to read them. The Java compiler recognizes that method to be the main method, and starts execution from there.

Code:

public static void main(String arg)

that method will not be recognized by the compiler, and you will get an error if no other main method exists.

[hardwired]

a — See the main method
b — run instead of main I don't know what you're talking about. Do you have an example of this?
c — when do we type static See Understanding Instance and Class Members

[Feng]

b — run instead of main I don't know what you're talking about. Do you have an example of this?

an examples (with the use of an external library though)

Code:

import acm.program.*;
public class AverageTwoDoubles extends ConsoleProgram {
	public void run() {
		println("This program averages two numbers.");
		double n1 = readDouble("Enter no1: ");
		double n2 = readDouble("Enter no2: ");
		double average = (n1 + n2) / 2;
		println("The average is " + average + ".");
	}
}

[staykovmarin]

Is ConsoleProgram a subclass of Thread, or is it implementing Runnable? If it was, then what you are doing when you create a run() method, is you are telling it what the thread will execute (by overriding the run() method)

If ConsoleProgram extends Thread:

Code:

AverageTwoDoubles avg = new AverageTwoDoubles();
avg.start()

That will run the code inside the run() method.


If ConsoleProgram implements Runnable

Code:

Thread t = new Thread(new AverageTwoDoubles());
t.start();

That will run the code in the run() method (again in a separate thread)

edit: if ConsoleProgram doesn't extend Thread, nor implement Runnable, then you are simply creating a method called run() that executes some code.