Char's questions

[Char]

newest questions in last post!!!!!!!!!!!

[camickr]

In the directory where you downloaded the JDK you should find a src.zip file which you can unzip.

[Char]

okay heres another one..im trying to do somekind of error handling system for my little program
well its for my school.

and i want to run a program with arguments like this:

java program -s 13

i want it to print out error message when i do not have 2 arguments given.
and also if the first argument isnt -s ... for example it is -t
and then stop program from workin..

i know i have to stop program with System class..i tried something this:

System.err.println("First argument is wrong.");

but it does not work correctly..or atleast i do not apply it corrently

need any help i can get.

[Tolls]

The normal technique is to do something like:

if (number of args isn't 2, or the first arg isn't "-s") {
    print out a description of useage.
    exit program
}
main program bits go here...

Now, the description of useage format can be found all over the place. You'll see it if you just do "java" from the command line. That's all there is to it, really.

[Char]

yeah tahts pretty much what im doin..i was just askin syntax..
but i think i got it workin now..maybe needs some optimization though

thanks for your help :)

	

class kaks_argumenti {
	public static void main(String[] args){
		if (args.length==2){
			double a = Double.parseDouble(args[1]);
			if (args[0].equals("-r")){
				System.out.println(Math.acos(a)+" radiaani.");
			}else if(args[0].equals("-d")){
				System.out.println((int)(Math.toDegrees(Math.acos(a)))+" kraadi.");
			}else{
					System.out.println("Etteantud lipud on tundmatud.");
					System.exit(0);
			}
		}else{
			System.out.println("Argumentide arv on vale.");
			System.exit(0);
		}
	}
}

[Tolls]

You also want to deal with the situation where they put more or less than 2 arguments to the program...and else, in other words.

[Char]

You also want to deal with the situation where they put more or less than 2 arguments to the program...and else, in other words.

yea im dealing with it..im saying "Wrong number of arguments"..and exit

thats all i need :)

[Tolls]

Whoops...missed that!
:)

[Char]

anyways im reallly really new to java, and doin everything in one class i think can't be too hard, but object oriented is crazy at the moment for me
i was programming all the basic stuff in python before..but i only did some methods and for,if statements..nothing hard

so can you guys give me a task with multible classes what is good for beginner, and i mean..like really beginner

[anthrax]

you can type into search engines like "java tutorials"

[Fubarable]

By your statements above and elsewhere in the forum, you don't seem new to programming, just Java. Why not take a favorite program of yours written in whatever language you know, and re-write it from the ground up in Java. For e.g., any programmer worth their salt has attempted one of these: zooming the Mandelbrot set, displaying the game of life or creating a Sudoku solver.

Have fun!

[Char]

i think this question was already here, but..how i format double

in python it was float

print("Circles area is: %0.2f"%(area))

how is it here?

System.out.printf("Circles area is: %0.2d",circle.area(4));

tried something this..but not workin
also i want 2 spots behind coma

[Fubarable]

%.2f can work for floating point numbers, but for me, there are too many unknowns here. What is a the circle variable, what does area(4) return. How are things not working? What errors are being shown? Have you set the locale? etc...

[Char]

well thanks it worked like that %0.2f

really thank you..you are the most active member in this forum and i see you helping people in all topics...

biggg ups for youuu :)

public class Ring extends Kujund {
	private int raadius;
	public Ring(int raadius){
		this.raadius=raadius;
	}
	public int getRaadius() {
		return raadius;
	}
	public void setRaadius(int raadius) {
		this.raadius = raadius;
	}
	public double ümbermõõt(int raadius){
		return 2*raadius*Math.PI;
	}
	public double pindala(int raadius){
		return Math.pow(raadius, 2)*Math.PI;
	}
	
}

public class Test {
	public static void main(String[] args){
		Ring ring=new Ring(4);
		Ruut ruut=new Ruut(5);
		System.out.printf("Ringi pindala on: %.2f",ring.pindala(ring.getRaadius()));
	}
}

btw there were my classes..ring is a circle class..and it has area and girth of it etc

[Fubarable]

This here bothers me:

public class Ring extends Kujund {
	private int raadius;
	public Ring(int raadius){
		this.raadius=raadius;
	}
	//..

	public double ümbermõõt(int raadius){
		return 2*raadius*Math.PI;
	}
	public double pindala(int raadius){
		return Math.pow(raadius, 2)*Math.PI;
	}
	
}

The last two methods ignore the radius field held by the object here:

private int raadius;

and allow you to pass as a parameter a new radius, that doesn't set the class's raadius field. Better I think would be have these two methods take no parameters, like so:

	public double ümbermõõt() {
		return 2*raadius*Math.PI;
	}
	public double pindala() {
		return Math.pow(raadius, 2)*Math.PI;
	}

This would allow the methods to use the raadius field held by the object.

[Char]

humm wait..i didnt exactly get what you mean?
why shouldnt i use that variable there when im using it inside method?
im a little confused.because english aint my mother tongue

[Fubarable]

Perhaps this is best explained with an example. Say we had a Student class that holds the student's name:

public class Student {
  private String name;

  public Student(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }
  
  public void displayInformation(String name) {
    System.out.println("Hi, my name is " + name);
  }
  
  public void displayInformation() {
    System.out.println("Hi, my name is " + name);
  }
  
}

There are two displayInformation methods here, one that takes no parameter:

  public void displayInfo() {
    System.out.println("Hi, my name is " + name);
  }

and one that takes a String parameter:

  public void displayInformation(String name) {
    System.out.println("Hi, my name is " + name);
  }

If you create a test program that uses this Student class like so:

public class TestStudent {
  public static void main(String[] args) {

    // create a new student whose name is set to "George Bush"
    Student student = new Student("George Bush");
    
    student.displayInformation();
    student.displayInformation("Barak Obama");
  }

}

You'll see that this is the output

Hi, my name is George Bush
Hi, my name is Barak Obama

The output from the parameterless method on top is correct since we are seeing the true name of the student. The output from the method that passes a parameter is not correct since its name parameter is "shadowing" the Student's name field; it's covering it over and giving us false information.

Make sense?

[Char]

yeah its kinda clear now.

[Char]

im trying to use robot class...but why it insists that i must use try and catch
i have no idea what they are..can someone explain

well my code is this..simple but even now i have error..

import java.awt.Color;
import java.awt.Robot;

public class Test {
	public static void main(String[] args){
		Robot robot1=new Robot();
		robot1.mouseMove(300, 200);
	}
}

[Tolls]

The Sun Exceptions tutorial page.