Event Driven Programming / No Main Method
Jan 29, 2015
I'm reading a book titled 'Intro to Java Programming'. I understand all the Main Method stuff. I'm now reading a chapter that talks about event driven programming. I know how to do this in VBA and in C#, ut I can't figure out how this works in Java. Here's the sample code that I'm trying to run.
import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.HBox;
import javafx.stage.Stage;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
[code]....
I'm using Net Beans IDE. When I paste that code into the IDE, I get all kinds of errors. Also, since there is no Main, I don't know how this is supposed to run. Java needs a Main Method for everything, I think. Does the Main call some kind of class?
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Feb 22, 2014
I think will be easy for me start with a GUI and then make things happens when the user clic on Buttons.Is there a good book about Event driven development on Java?
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Sep 10, 2014
exception in thread main java.lang.nullpointerexception code 45 and code 116
the lines are highlighted and no the code tags did not show up when I uploaded the file.
I typed '[code]' below:
Java Code: /**
This program demostrates rainfall for a year
*/
[Code].....
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Sep 20, 2014
I'm currently learning about Swing but I can't get my head round this piece of the code. Here is a simplified gui (not interested in the gui part but the execution)
public class SwingDemo implements ActionListener {
SwingDemo(){
JFrame jfrm = new JFrame("Simple gui pro");
//rest of code
public static void main(String[] args) {
new SwingDemo();
}
I get the above, create a new instance of SwingDemo in the main thread which starts up the gui through the constructor. However, then the tutorial says that I should avoid doing the above but do this instead:
public class SwingDemo implements ActionListener {
SwingDemo(){
JFrame jfrm = new JFrame("Simple gui pro");
//rest of code
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() { //why do this instead?
public void run(){
new SwingDemo();
}
});
}
}
Reading, it talks about an event-dispatching thread which has completely lost me... Why not just instantiate the object directly instead of creating another thread?
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Mar 4, 2014
I used java and jsf. I created dynamic datatable in java file. Can i call java method from setOnchange() event?
I am able to call java script function from setOnchange() event. See the below code which is working fine for java script.
HtmlSelectOneMenu selectOneMenu = new HtmlSelectOneMenu();
selectOneMenu.setStyleClass("dropdownStyleTwo");
selectOneMenu.setOnchange("openWin(this);IGNORE_UN LOAD=false");
I wrote openwin() function in java script. But i am not able to call java method change().
Code which is not working.
HtmlSelectOneMenu selectOneMenu = new HtmlSelectOneMenu();
selectOneMenu.setStyleClass("dropdownStyleTwo");
selectOneMenu.setOnchange("myclass.change();IGNORE _UNLOAD=false");
myclass is the bean of class Test. If user select any value from dropdown i want to call change java method. This function will apply the same selected dropdown value to the other record also.
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May 27, 2014
I'd like to know how to return a new array, I wrote in a method below the main method. I want to print the array but system.out.print doesn't work for arrays apparently. What structure i should use?
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May 27, 2014
I have to write a method called censor that gets an array of strings from the user as an argument and then returns an array of strings that contains all of the original strings in the same order except those with length of 4. For example if cat, dog, moose, lazy, with was entered, then it would return the exact same thing except for the words with and lazy.
Currently, my code so far just prints [Ljava.lang.String;@38cfdf and im stuck.
import java.util.Scanner;
public class censorProgram {
public static void main (String args[]){
Scanner input = new Scanner (System.in);
System.out.println ("How many words would you like to enter?");
int lineOfText = input.nextInt();
[Code] ....
I have to make new string array in the method and return words without four letters in the main method
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Feb 13, 2014
I am just trying to test this array, for a locker combination program that involves classes...but the array is printing out the whacky numbers for the location. When I try to call the method in the main, it does not work. How do I call a method that exist within a class into the main method?
public class locker {
public static void main(String[] args) {
CombinationLock();
[code]....
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Dec 30, 2014
I have two classes involved in this portion. CheckIn_Search
(class #1) is my main UI and I am collecting search information from the user in a jPanel form. When they click "Search" it passes the search criteria to a method that contacts a web service and gets the results. These results are passed to coSearchResults
(class #2) that opens a jFrame and jTable (in modal format, over the main window created by CheckIn_Search.
The user selects a row in the table and that selection data is passed back to coSearchResults to populate a new jPanel form. When the data is passed from coSearchResults, I want to close its window, hide the first jPanel in CheckIn_Search and make the second jPanel visible. To accomplish this, I created a method in CheckIn_Search that simply hides/shows the panels (it will do more later).
I instantiate and call the method in CoSearchResults as part of the button click event. The problem is, it doesn't work. The panels are unaffected and there are no errors. I've put in break-points and it goes into the method.. Here is the coSearch_Results code.
Here is am retrieving the jtable row id and using the first value in the row to get the data from the table model as there is more data than what is displayed in the table. I'm sending that whole row of data to the method that changes visibility.
private void btnOKActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_btnOKActionPerformed
// TODO add your handling code here:
int rowNum = jTable1.getSelectedRow();
String coNum = jTable1.getValueAt(rowNum,0).toString();
String[] text;
[code]....
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Feb 27, 2014
I am using mysql database and I have downloaded the library also I have managed to get the database connection and query working. I need to know if I need to create separate classes to add/remove/edit items and view items? Do I need to put my database connection script in every class that I create or should I create methods for both the connection and the queries that will be called in the additional classes or methods that I have?
Below is what I have written so far and it is working, I will change the database and query soon to reflect the task I need to do because I have followed a tutorial.
Java Code:
/**
* cdCollection.java
*/
package org.com.mm00422_prototype;
//Import for the SQL package
import java.sql.*;
//Registering the JDBC driver
//Class.forName("com.mysql.jdbc.Driver");
[code]....
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Jan 13, 2014
Here's a class called Fibonacci
Java Code:
public class Fibonacci {
public static int fib(int n) {
if (n < 2) {return n;}
else {return fib(n-1)+fib(n-2);}
[code]....
it contains one method called fib() and one main method.If I would want to have the main method in another class than fib(), how would I write the two classes? Only cutting the main method from this class to another one doesn't work.My question is, is the reason it doesn't work because I then would have to have a constructor in the Fibonacci class, and create a Fibonacci object first which I then use the method on?
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Dec 10, 2014
I have created a database driven Java app that i would like to deploy to several PCs. The App uses JReports which only worked when i installed Javac on this laptop. It worked fine within Netbeans but after building it depended on the java compiler and only worked after setting up Path variable..
Will i need to setup the Javac on every machine or is there any way of deploying it easier?
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Jul 23, 2014
I'm trying to make a TBG (Text Based Game) in Java for Android. Now, when I try to run it, it says No Main Method to run this program. The compiler also checks the program and tell me there are no errors.
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Oct 1, 2014
in java why main method is always static in nature...
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Jan 26, 2014
The idea is to create a program to add plants and retrieve plants from a Nursery. I created a class with the properties of the plants and also there is the class an Array list to keep track of the plants entered ( they will have to be printed later) (I am not too sure if adding a public class there is the best option.
The program will allow the user to pick and action and from there the code will do something. I don't want to have all the code inside 'main' The problem is in line 114.This is what I have so far.
Java Code:
package plant.nursery;
import java.util.ArrayList;
import java.util.Scanner;
/**Class to create a plant for a nursery.
public class PlantNursery
[code]....
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Apr 26, 2014
this is my program error occured run time,but compile sucessfully
{error msg-Error: Main method not found in class helloworldapp.HelloWorldApp, please define the main method as:
public static void main(String[] args)}
class HelloWorldApp
{
private int empno;
private float salary;
void setHelloWorldApp()
{
empno=12;
salary=1200;
[code]....
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Nov 17, 2014
I'm trying to call a method to my main method, but I can't seem to get it to work and it keeps resulting in a compile error.
import java.io.*;
import java.awt.Point;
import java.text.DecimalFormat;
import java.util.Random;
public class Chase {
public static void main(String args[]){
[Code] .....
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Sep 10, 2014
I have been reading about methods and I do have a beginner level understanding on how they work. I was trying to mess around and make a dog calculator using methods. I ran into a small snag; I cannot get the method to call to the main or the program to compile correctly. The first code below is the original. To me it looks like (based off of some examples I looked at) there should be no problems, but NetBeans gives me a few errors. 1) line 8- "cannot find symbol, variable dogYearCalc; 2) line 18 illegal start of expression; and 3) line 22 - unreachable statement.
import javax.swing.JOptionPane;
public class KrisExample {
public static void main (String[] args) {
double dogYears = 0;
JOptionPane.showInputDialog (null,"Please enter you dog's age in human years:");
[Code] ....
Someone told me that I was calling dogYearCalc without any arguments in your main method. I take that to mean that I needed to add it to the main, so I did here:
public static void main (String[] args, double dogYearCalc) {
That got rid of my first error, but then when I tried to run the program NetBeans said that I have no main class, so switched back to the original program above.
I thought that when I calling the dogYearCalc method on line 10 was the whole purpose of using a method. It seems to me that putting it somewhere in the main is counter productive.
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Jul 28, 2014
Can we recall the main method? I'm trying a code to recall main method (after the calling of JVM). I know this doesn't make any sense but I'm trying this just like that.
Code:
class derived {
public static void main(String args[]) {
System.out.println("Main Method class");
show();
}
static void show()
[code]....
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Jan 29, 2014
I've written a program just for the sake of it (to learn) and it seem's like theres quite a lot in the main method that perhaps could be split up into seperate classes. I'm not too sure where should start with this though, or what my thought process should have been as I was writing the program.
import java.util.Scanner;
public class Loops {
public static void main(String[] args) {
int answer = 16;
Scanner scan = new Scanner(System.in);
// Question
System.out.println("What is 4 x 4 ?");
[code]...
--- Update ---
here's a version without code comments as they might make it harder to read here -
import java.util.Scanner;
public class Loops {
public static void main(String[] args) {
int answer = 16;
Scanner scan = new Scanner(System.in);
System.out.println("What is 4 x 4 ?");
int userAnswerInt = 0;
[code]...
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Jan 7, 2014
What does void and static mean in the main method?
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Nov 1, 2014
I was reading the book, "Head First Java" and it was talking about how there may be multiple classes in a large application, but there will be only one main method.how does it work that way? How can you have multiple classes, but only one main method?
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Feb 9, 2014
This time I have to make a Black Jack game ( I guess this is a classic) I have created Three classes for this BlackJack( Main), Card, and Player.
What I am trying to do is put the Give one card to the player and remove it from the deck into a separate procedure because I will be doing this several times during the game.
This is the code I have so far Under the class BlackJack.
Java Code:
package black.jack;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Scanner;
[Code] .....
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May 7, 2015
I can call a child method from a main method. If I have a parent called "Assessment", a child called "Quiz", and another child called "test". Can I instinate an object like Assessment a = new test(); and call a method in test.I know the method can be called if I instinate the test t = new test() but that defeats the purpose of inheritance which I'm learning in class.
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Oct 26, 2014
When I try to call an object it can't find the symbol in the argument list. NetBeans says that it cannot find the movieCategory symbol when I try to call it. When I compile it to test a popup comes up that states "One or more projects were compiled with errors. Application you are running may end unexpectedly. I ran it anyways and everything runs up to the point of where it should call the object.
At this point it should get the Movie object and run the code within that, but if I put one of the categories it throws. "Exception in thread "main" java. lang.RuntimeException: Uncompilable source code - Erroneous tree type: <any>at MovieApp.main(MovieApp.java:33)Java Result: 1"
From my understanding to call an object it requires objectName.methodName(argumentList). Here is my Main method
/**
*This application will store a list of 100 movies and display them by category
*/
import java.util.Scanner;
public class MovieApp
{
public static void main(String args[])
{
//Displays <code>String</code> welcome message
System.out.println("Welcome to the Movie Application.");
System.out.println("There are 100 movies in the list.");
System.out.println("What category are you interested in?");
System.out.println();
[code].....
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Oct 10, 2014
I tried to create a simple program. The main method is supposed to call out the secondary method to use Scanner in order to ask a person to type in a number, which will be assigned to int x. Then the secondary method supposed to return the int x to main method, which supposed to print it out. And for some reason I just can't do it. No matter what the main method refusing to accept the int x.
import java.util.Scanner;
public class Return{
static Scanner newNum= new Scanner(System.in);
public static void main(String[] args){
getInt();
System.out.println(x);
}
public static getInt( ) {
// TODO Auto-generated method stub
int x;
System.out.print("give a num");
x= newNum.nextInt();
return x;
}}
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