1 odgovor na temo

[amater111]

Prosil bi za pomoč saj dobim nullpointerexception v currentPattern = (String)mesecBox.getSelectedItem(); ker sem še malo zelen pri programiranju bi prosil za nasvet, ker želim da se spremenljivke določijo šele po pritisku na gumb (seveda izbrane vrednosti ki jih izbereš v dropdown menu-ju). torej najbolj me zanima kako naj izvedem zanko v actionperformd zanki
Za kakeršen koli nasvet se zahvaljujem

package components;

import java.awt.*;
import java.awt.event.*;
import java.util.EventListener;

import javax.swing.*;

/* ComboBoxDemo2.java requires no other files. */
public class ComboBoxDemo2 extends JPanel implements ActionListener {
    /**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	static JFrame frame;
    JLabel result;
    JButton start;
    JComboBox mesecBox;
    JComboBox letoBox;
    String currentPattern = "";
    String currentPattern1 = "";
    Integer IzbraniMesec;
    Integer IzbranoLeto;
    
    public ComboBoxDemo2() {
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
        String[] meseci = {	"izberi mesec",
        					"Januar",
        					"Februar",
        					"Marec",
        					"April",
        					"Maj",
        					"Junij",
        					"Julij",
        					"Avgust",
        					"September",
        					"Oktober",
        					"November",
							"December"};
        String[] leta = {"2009",
        				 "2010",
        				 "2011",
        				 "2012",
        				 "2013",
        				 "2014",
        				 "2015"};

        currentPattern = meseci[0];
        currentPattern1 = leta[0];
        JLabel mesec = new JLabel("Mesec:");
        JLabel leto = new JLabel("Leto:");
        //Set up the UI for selecting a pattern.

        JComboBox mesecBox = new JComboBox(meseci);
        mesecBox.setEditable(true);
        mesecBox.addActionListener(this);
        
        JComboBox letoBox = new JComboBox(leta);
        letoBox.setEditable(true);
        letoBox.addActionListener(this);
        
        start = new JButton();
        start.setText("start");
        start.addActionListener(this);

        //Lay out everything.
        JPanel patternPanel = new JPanel();
        patternPanel.setLayout(new BoxLayout(patternPanel,BoxLayout.PAGE_AXIS));
        patternPanel.add(mesec);
        mesecBox.setAlignmentX(Component.LEFT_ALIGNMENT);
        patternPanel.add(mesecBox);

        JPanel patternPanel1 = new JPanel();
        patternPanel1.setLayout(new BoxLayout(patternPanel1,BoxLayout.PAGE_AXIS));
        patternPanel1.add(leto);
        letoBox.setAlignmentX(Component.LEFT_ALIGNMENT);
        patternPanel1.add(letoBox);
        
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new BoxLayout(buttonPanel,BoxLayout.PAGE_AXIS));
        buttonPanel.add(start);

        patternPanel.setAlignmentX(Component.LEFT_ALIGNMENT);
        patternPanel1.setAlignmentX(Component.LEFT_ALIGNMENT);

        add(patternPanel);
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(patternPanel1);
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(buttonPanel);

        setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
        reformat(currentPattern);
        reformatLeto(currentPattern1);
        
    } //constructor

    public void actionPerformed(ActionEvent e) {
    	if(e.getSource() == start);{
    		currentPattern = (String)mesecBox.getSelectedItem();
    		currentPattern1 = (String)letoBox.getSelectedItem();
        	IzbraniMesec = reformat(currentPattern);
        	IzbranoLeto = reformatLeto(currentPattern1);
    	}
    }

    /** Formats and displays today's date. */
    public static int reformat(String currentPattern) {
    	int a=0;
    	String m = currentPattern;
    	if(m=="izberi mesec")	a=0;
    	else if(m=="Januar")	a=1;
    	else if(m=="Februar")	a=2;
    	else if(m=="Marec")		a=3;
    	else if(m=="April")		a=4;
    	else if(m=="Maj")		a=5;
    	else if(m=="Junij")		a=6;
    	else if(m=="Julij")		a=7;
    	else if(m=="Avgust")	a=8;
    	else if(m=="September")	a=9;
    	else if(m=="Oktober")	a=10;
    	else if(m=="November")	a=11;
    	else if(m=="December")	a=12;        
        return a;
    }
    //reformats chosen year to integer
    public static int reformatLeto(String currentPattern1){
    	int a=0;
       	a = Integer.valueOf(currentPattern1);
    	if(currentPattern1 == "izberi leto"){
    		a=0;
    	}
    	return a;
    }
    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("ComboBoxDemo2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        JComponent newContentPane = new ComboBoxDemo2();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();        frame.setVisible(true);    }    public static void main(String[] args) {        //Schedule a job for the event-dispatching thread:        //creating and showing this application's GUI.        javax.swing.SwingUtilities.invokeLater(new Runnable() {            public void run() {                createAndShowGUI();            }        });    }}

[gapi_pro]

Nisem ravno prepričan ampak a je možno da ni izbran noben item v mesecBox? Debugiri in ustavi kodo na tej vrstici in poglej vrednost mesecBox-a.