Help a beginner with Java

[razaron]

<Original question answered>

Edit: I'll post more questions as I'm learning.

[streetfighter 2]

If you already have it working for classes why doesn't it work for javac? Maybe you just need to use something like "javac .\myfile.java"?

All you should need to do is add the Java directory to the "path" system variable.

[Easy Rhino]

set the path for it i believe.

[razaron]

How do you set the path for it? I've been reading around and am completely confused.

[razaron]

Another question.

Spoiler

In the following code:

public class Addition {
public Addition( ) {
int x, y = 1, z = 2;

x = y + z;
System.out.println("+ operator resulted in "+x);
}

public static void main(String args[]){
new Addition();
}
}

is

public Addition( ) {

the method header

int x, y = 1, z = 2;

x = y + z;
System.out.println("+ operator resulted in "+x);
}

the method body and

new Addition();

the method call?

[streetfighter 2]

Originally Posted by razaron

How do you set the path for it? I've been reading around and am completely confused.

Easiest way to do it is in System Properties (in Windows 7 you can use Start->Run->systempropertiesadvanced.exe).


Then select Environment Variables and you'll see this window.


Then click "Path" in the lower box and hit "Edit" and you'll get here:


Then just add a semicolon and the path to your Java directory (with javac).

Originally Posted by razaron

Another question.

I'm pretty sure that's correct, though my terminology is a bit rusty.

[razaron]

I ignored path and thought I had to add SOURCEPATH

Edit: I've already done that what I meant was how do I set it (cmd) to know where my .java files are, not javac.

[streetfighter 2]

Originally Posted by razaron

Edit: I've already done that what I meant was how do I set it (cmd) to now where my where my .java files are, not javac.

Well it doesn't really work that way as far as I know, but it does work the other way.

You have to type in the directory of your .java files at one time or another. The idea is usually to cd into the directory with your .java files and then all you need to do is type "javac myfile.java". You could also make a batch file which would simplify the process even further.

[Easy Rhino]

first off, not to be a dick, but you gotta correct your grammar. i had to read your question 3 times before i figured out what you were asking. better grammar means more people willing to help.

a .java file is the source code. you run javac on the .java file to compile it into a class file which you then execute running the java <your java class file>.

so you have to either be in the directory of your compiled java program or include the entire working directory.

[razaron]

I just changed the default start directory for a shortcut of cmd. That solves that problem.

Originally Posted by Easy Rhino

first off, not to be a dick, but you gotta correct your grammar. i had to read your question 3 times before i figured out what you were asking. better grammar means more people willing to help.

I couldn't think of a better way to word it (otherwise I would've just googled it...)

[razaron]

I popped my programing cherry.

Spoiler

import java.util.Scanner;

public class test {

public static void main(String args[]) {

Scanner input = new Scanner(System.in);

int a;
int b;
int c;

System.out.print("a = ");
a = input.nextInt();

System.out.print("b = ");
b = input.nextInt();

c = a + b;
System.out.print(c);
}
}

I'm going to practice with maths for now then do that archery thing Kreij mentioned in another thread.

PS. Is it bad to have to regularly look up syntax?

[A Cheese Danish]

Originally Posted by razaron

PS. Is it bad to have to regularly look up syntax?

Not at all for a beginner!
I still have to look up syntax for some things. The more you do it, the easier it will become and the less you will have to reference

[Kreij]

No raz, with 1000s of APIs and a jillion methods that are available in some of the modern programming languages, and the fact that with language revisions they will add/obsolete calls, you will be using references constantly.

[razaron]

I was looking for java keyword definitions and found them on Wikipedia. The definition of "void" has me confused.
Wikipedia defines void as, "The void keyword is used to declare that a method does not return any value.", if that's true how did the code I posted earlier return a value?

EDIT: Also, can any of you folks remember how long it took you to start using correct case letters (upper/lowercase) in code? That seems to be the commonest error I make.

[Jizzler]

That's because it didn't return anything, unlike this (poor) example:

public int getTheNumberTen() {
	return 10;
}

[razaron]

Then would I be correct in assuming returning a value means "returning a value to the code"?



Another question:
The following code makes cmd say "Your target is x" where x is a value.

System.out.println("Your target is " +x_target)

However I want cmd to say "Your target is x meters away" where x is a value. The code I'm using to make this happen is,

System.out.println("Your target is " +x_target " meters away")

, which doesn't work/compile. What do I have to do to make it work/compile?

[Jizzler]

Seems like you're missing a "+" after the x_target variable. You need it to concatenate " meters away" with the beginning portion.


That's one way to describe it. It's going to return the result so you may do with it as you will.

Ex: Lets say you have a function that returns a value describing how close a user got to the the target based on the angle, meters away, and the bow pull. It's something that you want to print out, but also save in an array so that the user can see their last ten moves or something like that.

proximity = getProximity(angle, meters, power)

Now you can print out the variable proximity and store it.

Note: Much more familiar with PHP, sorry if my Java syntax is off.

[razaron]

Is it better to have several small formulae,

u = Math.sqrt((2 * P * t_bow) / m);

t = (u * Math.sin(Math.toRadians(theta))) / 4.9;

x = Math.round(t * u * Math.cos(Math.toRadians(theta)) * 100)/100.0d;

or one big formula,

x = Math.round(((Math.sqrt((2 * P * t_bow) / m) * Math.sin(Math.toRadians(theta))) / 4.9) * u * Math.cos(Math.toRadians(theta)) * 100)/100.0d;

?

[razaron]

So far I have this for the archery game,

Spoiler

import java.util.Scanner;

public class archery{
public static void main(String args[]){
Scanner input = new Scanner(System.in);

double x_target;
double P;
double theta;
double u;
double t;
double x;
double s_target;
double d_target;
double m = 1.0;
double t_bow = 1.0;

System.out.println("Let's shot some arrows!");

x_target = 1 + (Math.round(100 * Math.random() * 100)/100.0d);
System.out.println("Your target is " +x_target+ " meters away");
System.out.println();

System.out.println("How much power will you pull the bow with: ");
P = input.nextDouble();
System.out.println();

System.out.println("At what angle will you shoot your arrow: ");
theta = input.nextDouble();
System.out.println();

u = Math.sqrt((2 * P * t_bow) / m);

t = (u * Math.sin(Math.toRadians(theta))) / 4.9;

x = Math.round(t * u * Math.cos(Math.toRadians(theta)) * 100)/100.0d;

s_target = x_target - x;

if (s_target < 0){
d_target = s_target * -1;
}
else{
d_target = s_target;
}

if (d_target > 1){
System.out.println("You were "+Math.round(d_target * 100) / 100.0d+" meters off");
}
else {
System.out.println("Well done you hit the target");
}
}
}

How do I make it return to the bit just after it's worked out "x_target" if "d_target" > 1?
Other than that it works, yay.

EDIT: I can advertise this game as using real Newtonian physics, lol.

[streetfighter 2]

Is this what you want?

Spoiler

 . . .

double d_target=2;

 . . . 

x_target = 1 + (Math.round(100 * Math.random() * 100)/100.0d);
while (d_target > 1) {
     System.out.println("Your target is " +x_target+ " meters away");
     System.out.println();

     System.out.println("How much power will you pull the bow with: ");
     P = input.nextDouble();
     System.out.println();

     System.out.println("At what angle will you shoot your arrow: ");
     theta = input.nextDouble();
     System.out.println();
     
     u = Math.sqrt((2 * P * t_bow) / m);

     t = (u * Math.sin(Math.toRadians(theta))) / 4.9;

     x = Math.round(t * u * Math.cos(Math.toRadians(theta)) * 100)/100.0d;

     s_target = x_target - x;

     if (s_target < 0){
          d_target = s_target * -1;
     }
     else{
          d_target = s_target;
     }

     if (d_target > 1){
          System.out.println("You were "+Math.round(d_target * 100) / 100.0d+" meters off");
     }
}
System.out.println("Well done you hit the target");

[razaron]

Originally Posted by streetfighter 2

Is this what you want?

Spoiler

 . . .

double d_target=2;

 . . . 

x_target = 1 + (Math.round(100 * Math.random() * 100)/100.0d);
while (d_target > 1) {
     System.out.println("Your target is " +x_target+ " meters away");
     System.out.println();

     System.out.println("How much power will you pull the bow with: ");
     P = input.nextDouble();
     System.out.println();

     System.out.println("At what angle will you shoot your arrow: ");
     theta = input.nextDouble();
     System.out.println();
     
     u = Math.sqrt((2 * P * t_bow) / m);

     t = (u * Math.sin(Math.toRadians(theta))) / 4.9;

     x = Math.round(t * u * Math.cos(Math.toRadians(theta)) * 100)/100.0d;

     s_target = x_target - x;

     if (s_target < 0){
          d_target = s_target * -1;
     }
     else{
          d_target = s_target;
     }

     if (d_target > 1){
          System.out.println("You were "+Math.round(d_target * 100) / 100.0d+" meters off");
     }
}
System.out.println("Well done you hit the target");

Couldn't get what you wrote to work. However that helped me learn the do-while thing, so thank you.

Here's my awesome game:

Spoiler

import java.util.Scanner;

public class archery{
public static void main(String args[]){
Scanner input = new Scanner(System.in);

double x_target;
double P;
double theta;
double u;
double t;
double x;
double s_target;
double d_target;
double m = 1.0;
double t_bow = 1.0;

System.out.println("Let's shot some arrows!");

x_target = 1 + (Math.round(100 * Math.random() * 100)/100.0d);
System.out.println("Your target is " +x_target+ " meters away");
System.out.println();

do {
System.out.println("How much power will you pull the bow with: ");
P = input.nextDouble();
System.out.println();

System.out.println("At what angle will you shoot your arrow: ");
theta = input.nextDouble();
System.out.println();

u = Math.sqrt((2 * P * t_bow) / m);

t = (u * Math.sin(Math.toRadians(theta))) / 4.9;

x = Math.round(t * u * Math.cos(Math.toRadians(theta)) * 100)/100.0d;

s_target = x_target - x;

if (s_target < 0){
d_target = s_target * -1;
}
else{
d_target = s_target;
}
if (d_target > 1){
System.out.println("You were "+Math.round(d_target * 100) / 100.0d+" meters off");
System.out.println();
}
else {
System.out.println("Well done you hit the target");
}
}
while (d_target > 1);


}
}

[razaron]

What would be a logical step up from the archery game? Preferably something that doesn't require much imagination (so no text adventure).

[PopcornMachine]

My advice is to learn Perl or Python or even C.

I hate Java. It's buggy as hell.

[streetfighter 2]

Originally Posted by razaron

What would be a logical step up from the archery game? Preferably something that doesn't require much imagination (so no text adventure).

Seeing as how 99% of the world does not use console applications, I'd suggest making a GUI for your archery game. The structure of GUI code is fairly similar in most languages, meaning they're mostly event driven. Here's the (rather poorly written IMO) official tutorial.

I'd create a simple window with a couple edit controls (text boxes) for inputting theta/P and a button to start the simulation. Then I'd plot the arrows path and show the origin and target.

It sounds complicated but it's actually very easy.

[razaron]

What am I doing wrong with this piece of code?

Spoiler

import java.util.*;

public class vectortest {

public static void main(String args[]){
Vector v = new Vector(5, 5);

while (int i = 0; i < 25; i++){
v.add(i, i);
}

int k = (int)v.get(4);
System.out.println(k);
}
}

I'm trying to make a 25 places big vector with each place containing an integer with the same value as the place itself (hence the (i, i)). Then it should display the 5th int in the vector.
The errors:

Spoiler