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How can I make a calendar using JComboBox?

I want to make it adaptive, like if Feb got 29 days in 2000 but it will change into 28 when 2001.
I want to do it while using JComboBox
How can I make action calendar using a combo box?
JComboBox jcb,jcb1,jcb2;
db(){
JFrame jf = new JFrame("register");
jf.setLayout=(new FlowLayout());
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("dd-MM-yyyy");
String aa1="0"+1+"-"+"0"+2+"-"+2000;
date = LocalDate.parse(aa1,dtf);
Integer day[] = new Integer[date.lengthOfMonth()];
for(int i=0;i<date.lengthOfMonth();i++) {
day[i]=i+1;
}
jcb = new JComboBox<>(day);
Integer month[] = new Integer[12];
for(int i=0;i<12;i++) {
month[i]=i+1;
}
jcb1 = new JComboBox<>(month);
Integer year[] = new Integer[80];
for(int i=0;i<80;i++) {
year[i]=i+1940;
}
jcb2 = new JComboBox<>(year);
jf.add(jcb);
jf.add(jcb1);
jf.add(jcb2);
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.setBounds(300,300,300,300);
jf.setVisible(true);
}

As #Andrew Thompson mentioned in comments, JComboBoxes for date selection is not a good idea. Take a look at Which one is the best Java datepicker.
However, if you still insist of using comboboxes, in order to achieve what you want, you will have to add an ActionListener to month/year combobox in order to re-fix the model (items) of days combobox.
Take a look at this example:
public class Test extends JFrame implements ActionListener {
private JComboBox<Integer> yearBox;
private JComboBox<Integer> monthBox;
private JComboBox<Integer> dayBox;
public Test() {
super("test");
setDefaultCloseOperation(EXIT_ON_CLOSE);
getContentPane().setLayout(new FlowLayout());
yearBox = new JComboBox<>();
for (int i = 1940; i <= LocalDateTime.now().getYear(); i++) {
yearBox.addItem(i);
}
yearBox.addActionListener(this);
monthBox = new JComboBox<>();
for (int i = 1; i <= 12; i++) {
monthBox.addItem(i);
}
monthBox.addActionListener(this);
dayBox = new JComboBox<>();
add(new JLabel("year:"));
add(yearBox);
add(new JLabel("month:"));
add(monthBox);
add(new JLabel("day:"));
add(dayBox);
//Start with current year selected
yearBox.setSelectedIndex(yearBox.getItemCount() - 1);
setSize(400, 400);
setLocationRelativeTo(null);
}
#Override
public void actionPerformed(ActionEvent e) {
int year = (int) yearBox.getSelectedItem();
int month = (int) monthBox.getSelectedItem();
int daysInThisMonth = LocalDate.of(year, month, 1).lengthOfMonth();
int previousSelection = dayBox.getSelectedItem() != null ? (int) dayBox.getSelectedItem() : 1;
dayBox.removeAllItems();
for (int i = 1; i <= daysInThisMonth; i++) {
dayBox.addItem(i);
}
if (previousSelection >= dayBox.getItemCount())
//select last index of month
dayBox.setSelectedIndex(dayBox.getItemCount() - 1);
else
dayBox.setSelectedItem(previousSelection);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(() -> new Test().setVisible(true));
}
}

Generate JFrames in a loop, naming issue

Beginner Java programmer here. I'm trying to create a card game to learn more about Java. I have an array of names I pulled out a database. For each String in the array I want to create a JPanel and inside JLabels where I will set the name, power, health, etc.
The problem is when I create these in a loop they all have the same name and overwrite each other. Since I read Java doesn't have dynamic Variable names, how do I solve this?
public void loadDatabaseCardElements(ArrayList cards) {
ArrayList<String> buildCards = cards;
int i;
for(i = 0; i != buildCards.size();) {
String var = buildCards.get(0);
//create the Panel etc
JPanel mainHolder = new JPanel();
mainHolder.setLayout(new BoxLayout(mainHolder, BoxLayout.PAGE_AXIS));
JLabel name = new JLabel("Name: " + var);
JLabel powerLabel = new JLabel("Power: ");
JLabel healthLabel = new JLabel("Health: ");
JLabel armorLabel = new JLabel("Armor: ");
JLabel type1Label = new JLabel("Type1");
JLabel type2Label = new JLabel("Type2: ");
JLabel ability1Label = new JLabel("Ability1: ");
JLabel ability2Label = new JLabel("Ability2: ");
JLabel ability3Label = new JLabel("Ability3: ");
JButton card1 = new JButton("Add to deck");
mainHolder.add(name);
mainHolder.add(powerLabel);
mainHolder.add(healthLabel);
mainHolder.add(armorLabel);
mainHolder.add(type1Label);
mainHolder.add(type2Label);
mainHolder.add(ability1Label);
mainHolder.add(ability2Label);
mainHolder.add(ability3Label);
mainHolder.add(card1);
mainHolder.setBorder(BorderFactory.createLineBorder(Color.black));
mainHolder.setPreferredSize( new Dimension( 130, 200 ) );
frame1.add(mainHolder, BorderLayout.WEST);
SwingUtilities.updateComponentTreeUI(frame1);
card1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
preDeck.add(var); //add to another array when clicked
}
});
if (buildCards.size() != 0) {
buildCards.remove(0);
} else {
}
}
}

The reason for overwriting all the panels with same name is due to this part of your code:
int i;
for(i = 0; i != buildCards.size();) {
String var = buildCards.get(0);
You are assigning the first element of your list to each JLabel. This could help you achieve what you need:
for(int i = 0; i < buildCards.size(); i++){
String var = buildCards.get(i);
// Followed by your code
}

set a growable layout for a standard jpanel in the frame and then add a new jpanel to the standard jpanel every time. this should solve the naming problem. if u need access to each panel, you can store them in an array

*new title: JButton array scope (it was:change color of button with button name)

How can is alter the color of the correct button?
It is for a small application, this app has 5 buttons from a array.(the name's are a,b,c,d,e)
The appearence of the buttons have to alter (change color) when i type in a number in a Jtextfield.
I added a name to each button:
knop = new JButton(Titel[i]);
knop.setName(tel[i]);
Here i get the text:
public void actionPerformed(ActionEvent e) {
String invoer = antwoord.getText();
try
{
int welke = Integer.parseInt(invoer);
if (welke-1 >0 && welke-1<5)
{
vraag.setText("Goeie keus!");
if (welke == 1){
knop.setBackground(Color.BLUE);
}
knop.setBackground(Color.red);
}
But now it only changes the last button to red which is created bij the array.
So the question can I select a button by its name?
So if (input = 1) alter button 1 to green. in stead of only button 5.
I have tried de solution of gile, but i can't get it to work:
I get every time a: "AWT-EventQueue-0" java.lang.NullPointerException"
package kiesknop;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
//public class Paneel extends JApplet
public class Paneel extends JFrame
{
private JPanel paneel;
private JButton knop;
public JTextField antwoord;
private JLabel vraag;
public JButton[] knops;
public Paneel() {
int [][] numButtons = new int [5][4];
numButtons[0][0] = 50;
numButtons[0][1] = 10;
numButtons[0][2] = 10;
numButtons[0][3] = 10;
numButtons[1][0] = 100;
numButtons[1][1] = 10;
numButtons[1][2] = 30;
numButtons[1][3] = 30;
numButtons[2][0] = 200;
numButtons[2][1] = 10;
numButtons[2][2] = 50;
numButtons[2][3] = 50;
numButtons[3][0] = 300;
numButtons[3][1] = 10;
numButtons[3][2] = 100;
numButtons[3][3] = 100;
numButtons[4][0] = 500;
numButtons[4][1] = 10;
numButtons[4][2] = 200;
numButtons[4][3] = 200;
String [] Titel = new String [5];
Titel [0] = "*";
Titel [1] = "**";
Titel [2] = "***";
Titel [3] = "****";
Titel [4] = "*****";
String [] tel = new String [5];
tel [0] = "a";
tel [1] = "b";
tel [2] = "c";
tel [3] = "d";
tel [4] = "e";
paneel = new JPanel();
JButton[] knops = new JButton[5];
for (int i = 0; i < 5; i++)
{
knops[i] = new JButton(Titel[i]);
knops[i].setName (tel[i]);
knops[i].setBounds(numButtons[i][0],numButtons[i][1], numButtons[i][2], numButtons[i][3]);
knops[i].addActionListener(new KnopHandler());
}
for (int i = 0; i < 5; i++)
{
paneel.add(knops[i]);
}
vraag = new JLabel("Welke knop grootte vind je het mooist?");
vraag.setBounds(100, 400, 250, 20);
antwoord = new JTextField(20);
antwoord.setBounds(500, 400, 100, 20);
antwoord.setEditable(true);
antwoord.addActionListener(new AntwoordHandler());
paneel.add (vraag);
paneel.add (antwoord);
setContentPane (paneel);
}
public class KnopHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
JButton o = (JButton)e.getSource();
String Text = o.getText();
String name = o.getName();
String Label =o.getLabel();
System.out.println("knop gedrukt");
System.out.println(Text);
System.out.println(name);
System.out.println(Label);
}
}
class AntwoordHandler implements ActionListener {
public void actionPerformed(ActionEvent e) {
String invoer = antwoord.getText();
try
{
int welke = Integer.parseInt(invoer);
if (welke >0 && welke<5)
{
vraag.setText("Goeie keus!");
if(welke == 1)// knops[welke].setBackground(Color.BLUE);
System.out.println(knops[1]);
if(welke == 2) knops[welke].setBackground(Color.BLUE);
if(welke == 3) knops[welke].setBackground(Color.BLUE);
if(welke == 4) knops[welke].setBackground(Color.BLUE);
if(welke == 5) knops[welke].setBackground(Color.BLUE);
}
else vraag.setText("Geen geldige invoer!");
}
catch( NumberFormatException nfe)
{
if( invoer.equals("")) vraag.setText("Niets ingevuld!");
else
vraag.setText("Alleen nummers invoeren!");
}
}
}
public static void main (String arg[])
{
JFrame frame = new Paneel();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(null);
frame.setVisible(true);
frame.setSize(900, 500);
}
}
What am i doing wrong ?

You can put buttons in an array
JButton[] knops = new JButton[5];
...
knops[i] = new JButton(Titel[i]);
...
And then set the background after user entered a number:
if (welke == 1){
knops[welke].setBackground(Color.GREEN);
}

Your title doesn't match with the given example: you are asking to get a button reference with string name but you are trying to parse the name to an integer.
However, if i understood your requirement correctly: I can think of two option:
Traverse each button of the button's array you have and compare with their name with your target name: you can get the name of the component(JButton) invoking button.getName().
Instead of using array which require traverse each time to get the target button with matching name, Create a HashMap<key, value>: HashMap<String, JButton>, map the button to their name and use it to get the component on Action Event.
HashMap<String, JButton>buttomMap = new HashMap<>();
buttonMap.put("kicker", kickerButton); // kickButton is a button
//// Then in actionPerformed() function
JButton button = buttonMap.get("kicker");
button.setBackground(Color.BLUE);

setCharAt a for JLabel

I'm trying to replace setCharAt with something that can be used with a JLabel... I've been on oracle doc's looking for a solution. i don't know if I'm looking for the wrong thing or it just doesn't exists.. if it doesn't exists how could i work around that? i understand my naming convention is off and will be changing them as soon as possible...
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import javax.swing.*;
public class HangmanPanel extends JPanel {
static Boolean FOUND;
private static final long serialVersionUID = -5793357804828609325L;
public static String answerKey() {
//get random array element
String array[] = new String[10];
array[0] = "hamlet";
array[1] = "mysts of avalon";
array[2] = "the iliad";
array[3] = "tales from edger allan poe";
array[4] = "the children of hurin";
array[5] = "the red b" +
"+adge of courage";
array[6] = "of mice and men";
array[7] = "utopia";
array[8] = "chariots of the gods";
array[9] = "a brief history of time";
ArrayList<String> list = new ArrayList<String>(Arrays.asList(array));
Collections.shuffle(list);
String s = list.get(0);
return s;
}
public StringBuilder dashReplace(String s) {
//replace non-white space char with dashes and creates StringBuilder Object
String tW = s.replaceAll("\\S", "-");
System.out.print(tW + "\n");
StringBuilder AnswerKey = new StringBuilder(tW);
return AnswerKey;
}
public static int findAndReplace(String s, JLabel answerKey, String sc,
char ch) {
//find position of user input and replace
int pos = -1;
FOUND = false;
while(true){
pos = s.indexOf(sc, pos+1);
if(pos < 0){
break;
}else{
FOUND = true;
//setCharAt dosen't work for JLable
answerKey.setCharAt(pos, ch);
}
}
JLabel AnswerKey2 = new JLabel(answerKey.toString());
return pos;
}
public HangmanPanel(final String s){
this.setLayout(null);
JLabel heading = new JLabel("Welcome to the Hangman App");
JButton Button = new JButton("Ok");
//get input
JLabel tfLable = new JLabel("Please Enter a Letter:");
final JLabel AnswerKey = new JLabel(dashReplace(answerKey()).toString());
final JTextField text = new JTextField(10);
heading.setSize(200, 50);
tfLable.setSize(150, 50);
text.setSize(50, 30);
Button.setSize(60, 20);
AnswerKey.setSize(200, 100);
heading.setLocation(300, 10);
tfLable.setLocation(50, 40);
text.setLocation(50, 80);
Button.setLocation(100, 85);
AnswerKey.setLocation(100,85);
this.add(heading);
this.add(tfLable);
this.add(text);
this.add(Button);
this.add(AnswerKey);
Button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// can't access text
String sc = text.getText();
char ch = sc.charAt(0);
findAndReplace(s, AnswerKey, sc, ch);
}
});
}
}

Why are you trying to use setCharAt(...) with a JLabel. A label is meant to display static text. The only way to change it is to replace the entire string.
I guess you could do something like:
StringBuilder text = label.getText();
text.setCharAt(...);
label.setText( text.toString() );
Another option would be to use a JTextField that looks like a JLabel:
JTextField label = new JTextField(...);
label.setEditable(false);
label.setBorder(null);
label.setOpaque(false);
Then when you need to change the text you could do:
label.select(...);
label.replaceSelection(...);

The only method available for setting text for JLabel components is setText. Also Strings are immutable. Therefore, you can use StringBuilder:
StringBuilder builder = new StringBuilder(answerKey.getText());
builder.setCharAt(pos, ch);
answerKey.setText(builder.toString());

Adding a JPanel Array to a Container

Look at the Last line of code, that Is where I specifically would like to add my JPanel array to a container. Thanks alot Guys or Gals!
Code:
private JFrame b = new JFrame("Lotus");
private JLabel currentP = new JLabel();
private int currentS;
private Container pieces = new Container();
private JButton exitt = new JButton("EXIT");
private ImageIcon B1=new ImageIcon("C:\\Users\\Brusty\\Downloads\\p1.jpg");
private ImageIcon B2=new ImageIcon("C:\\Users\\Brusty\\Downloads\\p2.jpg");
LinkedList<Stack<Integer>> spotList = new LinkedList<Stack<Integer>>();
//Creation of Gamepiece labels
public void Labels(){
JLabel[] labelsP1 = new JLabel[10];
JLabel[] labelsP2 = new JLabel[10];
for(int i = 0 ; i < labelsP1.length ; i++){
labelsP1[i] = new JLabel(B1);
for(int j = 0 ; j < labelsP2.length ; j++){
labelsP2[j] = new JLabel(B2);
}
Container c = b.getContentPane();
c.setLayout(new GridLayout(13,3));
c.add(pieces);
pieces.add(labelsP1);

Not sure I really see your problem. You just need to loop through the labelsP1 array and add the labels...
for (JLabel label : labelsP1) {
pieces.add(label);
}