Thread: Help with password generation

I'm making a program to generate a random password with the desired length and chars.

All went smooth until i got to the generation itself. The error exists in this code:

package generate;
 
import gui.PassPanel;
 
import java.util.Random;
 
public class GeneratePass {
 
	private final String[] letters = new String[] {
			"a","A","b","B","c","C","d","D","e","E","f","F","g","G","h","H",
			"i","I","j","J","k","K","l","L","m","M","n","N","o","O","p","P",
			"q","Q","r","R","s","S","t","T","u","U","v","V","w","W","x","X",
			"y","Y","z","Z"
	};
 
	private final String[] numbers = new String[] {
			"0","1","2","3","4","5","6","7","8","9"
	};
 
	private final String[] both = new String[] {
			"a","A","b","B","c","C","d","D","e","E","f","F","g","G","h","H",
			"i","I","j","J","k","K","l","L","m","M","n","N","o","O","p","P",
			"q","Q","r","R","s","S","t","T","u","U","v","V","w","W","x","X",
			"y","Y","z","Z","0","1","2","3","4","5","6","7","8","9"
	};
 
	String pass = "";
 
	public GeneratePass(String chars, int length) {
		String[] charsUsing;
		if (chars.equals("both")) {
			charsUsing = both;
		}
		else if (chars.equals("letters")) {
			charsUsing = letters;
		}
		else{
			charsUsing = numbers;
		}
 
		Random r = new Random(charsUsing.length);
 
		for (int i = 0; i < length; i++) {
			pass = pass + charsUsing[r.nextInt()];
		}
 
		PassPanel.setPassword(pass);
	}
}

And I get this exception:

 

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: -1165488049

	at generate.GeneratePass.<init>(GeneratePass.java:44)

	at gui.PassPanel$MyOkButtonListener.actionPerformed(P  assPanel.java:103)

	at javax.swing.AbstractButton.fireActionPerformed(Abs  tractButton.java:2012)

	at javax.swing.AbstractButton$Handler.actionPerformed  (AbstractButton.java:2335)

	at javax.swing.DefaultButtonModel.fireActionPerformed  (DefaultButtonModel.java:404)

	at javax.swing.DefaultButtonModel.setPressed(DefaultB  uttonModel.java:259)

	at javax.swing.plaf.basic.BasicButtonListener.mouseRe  leased(BasicButtonListener.java:252)

	at java.awt.Component.processMouseEvent(Component.jav  a:6268)

	at javax.swing.JComponent.processMouseEvent(JComponen  t.java:3267)

	at java.awt.Component.processEvent(Component.java:603  3)

	at java.awt.Container.processEvent(Container.java:204  5)

	at java.awt.Component.dispatchEventImpl(Component.jav  a:4629)

	at java.awt.Container.dispatchEventImpl(Container.jav  a:2103)

	at java.awt.Component.dispatchEvent(Component.java:44  55)

	at java.awt.LightweightDispatcher.retargetMouseEvent(  Container.java:4633)

	at java.awt.LightweightDispatcher.processMouseEvent(C  ontainer.java:4297)

	at java.awt.LightweightDispatcher.dispatchEvent(Conta  iner.java:4227)

	at java.awt.Container.dispatchEventImpl(Container.jav  a:2089)

	at java.awt.Window.dispatchEventImpl(Window.java:2517  )

	at java.awt.Component.dispatchEvent(Component.java:44  55)

	at java.awt.EventQueue.dispatchEventImpl(EventQueue.j  ava:649)

	at java.awt.EventQueue.access$000(EventQueue.java:96)

	at java.awt.EventQueue$1.run(EventQueue.java:608)

	at java.awt.EventQueue$1.run(EventQueue.java:606)

	at java.security.AccessController.doPrivileged(Native Method)

	at java.security.AccessControlContext$1.doIntersectio  nPrivilege(AccessControlContext.java:105)

	at java.security.AccessControlContext$1.doIntersectio  nPrivilege(AccessControlContext.java:116)

	at java.awt.EventQueue$2.run(EventQueue.java:622)

	at java.awt.EventQueue$2.run(EventQueue.java:620)

	at java.security.AccessController.doPrivileged(Native Method)

	at java.security.AccessControlContext$1.doIntersectio  nPrivilege(AccessControlContext.java:105)

	at java.awt.EventQueue.dispatchEvent(EventQueue.java:  619)

	at java.awt.EventDispatchThread.pumpOneEventForFilter  s(EventDispatchThread.java:275)

	at java.awt.EventDispatchThread.pumpEventsForFilter(E  ventDispatchThread.java:200)

	at java.awt.EventDispatchThread.pumpEventsForHierarch  y(EventDispatchThread.java:190)

	at java.awt.EventDispatchThread.pumpEvents(EventDispa  tchThread.java:185)

	at java.awt.EventDispatchThread.pumpEvents(EventDispa  tchThread.java:177)

	at java.awt.EventDispatchThread.run(EventDispatchThre  ad.java:138)

It points to this line of code:

pass = pass + charsUsing[r.nextInt()];

Please help me!