Deve ser algum erro de parametro

package view;
import javax.swing.JOptionPane;
import source.Cliente;



 private void btnOkActionPerformed(java.awt.event.ActionEvent evt) {
        String n = txtN.getText();
        int q = txtN.getText().length();
                
        Cliente c = new Cliente(n, q);
        c.resolve();
        c.imprimir();
      
                
    }

package source;
import view.FrmCliente;
import javax.swing.JOptionPane;

    public class Cliente {
        private String n = "";  // numeros digitados
        private int q = 0;  // quantidade caracteres armazenados
        private String resu = "";
        
  
    public Cliente(){        
    }
    
    /** Criar instancia dos valores armazenados */
    public Cliente(String n, int q) {
        this.setN(n);
        this.setQ(q);
    }
      
      
    /** Pegar valor dos atributos */
    public String getN() {
        return n;
    }

    public int getQ() {
        return q;
    }

    /** Alterar valor dos atributos */
    public void setN(String n) {
        this.n = n;
    }

    public void setQ(int q){
        this.q =q;
    }
 
    
   public String getResu(){
       return resu;
   } 
   
 
   
   public void setResu(String resu){
       this.resu = resu;
   }
   

     public void resolve(){
          for (int i = 1; i <= this.q; ++i) {
            this.resu = this.n.charAt(i) + this.resu;
                 
          }   
    }    
      
     public void imprimir(){
         JOptionPane.showMessageDialog(null, "Valor é " +this.resu);
     }
 
}

Exception in thread "AWT-EventQueue-0" java.lang.StringIndexOutOfBoundsException: String index out of range: 3
        at java.lang.String.charAt(String.java:558)
        at source.Cliente.resolve(Cliente.java:64)
        at view.FrmCliente.jButton1ActionPerformed(FrmCliente.java:71)
        at view.FrmCliente.access$000(FrmCliente.java:15)
        at view.FrmCliente$1.actionPerformed(FrmCliente.java:55)
        at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1849)
        at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2169)
        at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
        at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:234)
        at java.awt.Component.processMouseEvent(Component.java:5488)
        at javax.swing.JComponent.processMouseEvent(JComponent.java:3126)
        at java.awt.Component.processEvent(Component.java:5253)
        at java.awt.Container.processEvent(Container.java:1966)
        at java.awt.Component.dispatchEventImpl(Component.java:3955)
        at java.awt.Container.dispatchEventImpl(Container.java:2024)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4212)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3892)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3822)
        at java.awt.Container.dispatchEventImpl(Container.java:2010)
        at java.awt.Window.dispatchEventImpl(Window.java:1774)
        at java.awt.Component.dispatchEvent(Component.java:3803)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:463)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)

BUILD SUCCESSFUL (total time: 5 minutes 1 second)