We Keep Coding

How to enable a JButton on a condition?

I'm trying to create a JButton that enables when certain conditions are met. The program sets setEnabled(false) as initial value, but after an update, it should be setEnabled(true).
I tried several things. Here some code:
public class SwimAction extends AbstractAction {
private final PoolModel poolModel;
private final Swimmer swimmer;
public SwimAction(PoolModel poolModel, Swimmer swimmer) {
super("GO!");
this.poolModel = poolModel;
this.swimmer = swimmer;
// default
setEnabled(false);
}
I tried the following:
// Replaced the setEnabled(false) by setEnabled(checkGo())
public boolean checkGo(){
return(pool.isNotOccupied());
}
// Overwrite setEnabled
#Overwrite
public void setEnabled(boolean bool){
boolean oldBool = this.enabled;
if (oldBool != bool && pool.isNotOccupied()) {
this.enabled = bool;
this.firePropertyChange("enabled", oldBool, bool);
}
}
However, none of them worked. Anyone knows how to enable the button when a certain condition (pool.isNotOccupied()) is met?

Seems like you need to listener for a change in the state of the pool object's occupied property, and the best way to do this is to give it a listener of some sort. This could be as simple as a ChangeListener or perhaps better, a PropertyChangeListener. The details of the best solution would likely depend much on the structure of your program, of the rest of the code that we can't see, but, if PoolModel is what you're listening to, what if you gave it...
public class PoolModel {
public static final String OCCUPIED = "occupied";
private PropertyChangeSupport propChangeSupport = new PropertyChangeSupport(this);
private boolean occupied;
public void addPropertyChangeListener(PropertyChangeListener l) {
propChangeSupport.addPropertyChangeListener(l);
}
// also have a remove listener
public boolean isOccupied() {
return occupied;
}
public void setOccupied(boolean occupied) {
boolean oldValue = this.occupied;
boolean newValue = occupied;
this.occupied = occupied;
propChangeSupport.firePropertyChange(OCCUPIED, oldValue, newValue);
}
// ......
And then in the code that uses it:
poolModel.addPropertyChangeListener(pcEvent -> {
if (pcEvent.getPropertyName().equals(OCCUPIED)) {
setEnabled((boolean) pcEvent.getNewValue());
}
});

Getting Variables From Java constructor

I'm new to Java programming, sorry if this is a dumb question.
I find it hard to word this question properly, but I have an assignment to create a aircraft class that can make aircraft land, takeoff etc. And need to test it using Testclass. When the new object are entered it automatically assigns a unique ID to the aircraft in the constructor.
I can do this using a instance method fine as it has a return value which is returned to to Testclass. The question wants me to do this in the constructor itself, however, the constructor never returns anything. So the variable never gets sent to the Testclass. I clearly am not understanding OOP properly. Even when I try to just use a getter method to get the ID created in the constructor it gives me the initialized variable before the the constructor has worked on this. This is the code I have so far and its completely wrong I know but if someone could point me in the right direction or tell me how to word this question better it would be a massive help.
// I need to enter 3 aircraft into the system in the testclass
public class Aircraft {
private int aircraftID;
private static int lastID;
private String airportcode;
private int ID = 100;
private int count;
public Aircraft(int a, int b, int c){
// Constructor
// Assign ID
this.ID = a;
lastID = ID;
ID++;
this.ID =b;
lastID = ID;
ID++;
}
}

OK, you want to create an Aircraft that has an automatically-assigned unique identifier, and can take off and land. That implies you need a field for tracking the identifier, a field for tracking whether it's in the air (or not), and methods for the take off and land operations. You also need a static field for generating the unique identifiers. (Note that this implementation isn't thread safe.)
private class Aircraft {
private static int staticId = 0;
private int uniqueId = 0;
private boolean onGround = true; // Aircraft start on the ground in this implementation
public Aircraft(){
this.uniqueId = staticId; // putting this line first makes uniqueId zero-indexed in effect
staticId++;
}
public void land(){
onGround = true;
}
public void takeoff(){
onGround = false;
}
public boolean isFlying(){
return !onGround; // If it's not on the ground, it's flying
}
public int getUniqueId(){
return uniqueId;
}
}
Unit tests checks all of the methods and expected functionality of the class in question:
import org.junit.Test;
import static org.junit.Assert.*;
import Aircraft;
class Testclass {
private final Aircraft aircraft = new Aircraft();
#Test
public void hasId(){
aircraft.getUniqueId() >= 0;
}
#Test
public void canLand(){
assertTrue(aircraft.land());
}
#Test
public void canTakeOff(){
assertTrue(aircraft.takeOff());
}
#Test
public void checkFlightOperationsAreTrackedCorrectly(){
aircraft.land();
assertFalse(aircraft.isFlying());
aircraft.takeOff();
assertTrue(aircraft.isFlying());
}
}

As pointed out a constructor does not return anything (the simplified version is that with new it returns an object instance). I am kinda guessing at what you are trying to acomplish, but I'll have a go anyways. It seems to me that you are trying to cram the construction of 3 objects into one constructor - which is why your constructor has 3 parameters. Also you are playing havoc with the IDs.
I have removed all the variables that I didnt quite understand, leaving only ID that increments with each instantiated Aircraft. The #Override is mainly just for show.
public class Aircraft {
private int aircraftID;
private static int lastID = 0;
#Override
public String toString(){
return "Aircraft_" + this.aircraftID;
}
public Aircraft() {
lastID++;
this.aircraftID = lastID;
}
}
I took the liberty and wrote the TestClass just to see if we have the same thing in mind. Again the printAircraft() method is for show.
public class TestClass {
private List<Aircraft> aircrafts;
public TestClass(){
aircrafts = new ArrayList<>();
}
public void addAircraft(Aircraft a){
aircrafts.add(a);
}
public void printAircraft(){
Iterator<Aircraft> it = aircrafts.iterator();
while(it.hasNext()){
System.out.println(it.next().toString());
}
}
}
and to test it, we create and instance of TestClass add 3 Aircraft instances and print out the contents
public static void main(String[] args) {
TestClass tc = new TestClass();
tc.addAircraft(new Aircraft());
tc.addAircraft(new Aircraft());
tc.addAircraft(new Aircraft());
tc.printAircraft();
}
This would be the case if you are to write the TestClass. If that is given, it would help to know what it looks like - maybe that would help us understand better.

Calling a method originated from a switch case from another class

I am relatively new to java and I have been assigned a project. I need to make a rather complicated(for a newbie) battleship game.
Here, I try to call switch cases in class Player from class Tile. Since I've read that one can't directly have access to a switch case, I have made the methods caseSea(), caseShip() e.t.c.
When trying to call them in class Player I get a 'void' type not allowed here error, which I understand but have no idea how to fix!
Any help would be appreciated thanks!
Here is class Tile created to represent one block of a 2D array that will become the battleground board:
public class Tile
{
private int x,y;
static boolean hidden;
public Action tile_action;
public enum Action
{
Sea,
Ship,
Hit,
Miss
}
Action action;
public Tile(Action action)
{
this.action=action;
this.x = x;
this.y = y;
this.tile_action = action;
}
public static void caseSea()
{
System.out.println("~");
}
public static void caseShip()
{
if(hidden == true)
System.out.println("~");
else
System.out.println("s");
}
public static void caseHit()
{
System.out.println("X");
}
public static void caseMiss()
{
System.out.println("O");
}
public static void draw(Action action)
{
switch(action)
{
case Sea:
caseSea();
break;
case Ship:
caseShip();
break;
case Hit:
caseHit();
break;
case Miss:
caseMiss();
break;
}
}
}
Also here is class Player which contains the call to the switch case:
import java.util.Scanner;
public class Player
{
String username; //Variable declaration
static int shotcount;
static int misscount;
static int hitcount;
static int repeatshot;
private int HitPosition[][] = new int[10][10];
public Player(String username)
{
this.username = username;
}
private void placeAllShips()
{
//super.placeAllShips();
}
public void fire(int pos[],int board,boolean hit)
{
if(hit == true)
{
HitPosition[pos[0]][pos[1]] = Tile.draw(Tile.caseHit());
shotcount++;
hitcount++;
}
else
{
HitPosition[pos[0]][pos[1]] = Tile.draw(Tile.caseMiss());
shotcount++;
misscount++;
}
}
}
I get the error that I mention above, in Tile.draw(Tile.caseHit()) and Tile.draw(Tile.caseMiss())

Heh, since this is a relatively simple issue I wanted to stick to comments, but I feel I need to make my voice since the other answers are simply wrong.
What the other guys are suggesting is changing the return type of the methods, and that indeed can work but not with the code you have.
They would ultimately be called twice, and thats not what you want.
The call order would be
caseHit()
pass the caseHit()'s value to draw()
enter a switch inside the draw() method with the Hit enum value and ultimately call caseHit() again.
This is not what you want to do. All you wanna do is call the draw() method with the right argument, which in this case is one of the Action enum values.
So ultimately there is a very easy way to fix your code without much changes and this is changing
Tile.draw(Tile.caseHit());
to
Tile.draw(Tile.Action.Hit);
(and by analogy the other calls of this method)

With Tile.draw(Tile.caseHit()) you are trying to call the caseHit() method and sending the return value of that method as a parameter to the draw() method. The problem is that the caseHit() method isn't returning anything as it has a void return type.
You could fix this by making the caseHit() method return an Action:
public static Action caseHit() {
return Action.Hit;
}

Java Inheritance : 2nd instance calls 1st instance method

I have a very strange problem with a java class in my android application.
I have some sub classes which extend my abstract class GameDialog
GameDialog class
public abstract class GameDialog extends Sprite
{
private static boolean gd_visible = false;
protected GameDialog(GameScene scene, Camera camera, VertexBufferObjectManager pSpriteVertexBufferObject){
...
}
public boolean display(){
if(!GameDialog.gd_visible) {
...
}
}
protected boolean hide(){
if(GameDialog.gd_visible){
...
}
}
}
PauseDialog class
public class PauseDialog extends GameDialog {
public PauseDialog(GameScene scene, Camera camera, VertexBufferObjectManager pSpriteVertexBufferObject) {
super(scene, camera, pSpriteVertexBufferObject);
...
final ButtonSprite play_button = new ButtonSprite(...);
play_button.setOnClickListener(setPlayButtonListener());
}
private OnClickListener setPlayButtonListener() {
return new OnClickListener() {
#Override
public void onClick(ButtonSprite pButtonSprite, float pTouchAreaLocalX, float pTouchAreaLocalY) {
hide();
}
};
}
}
Each time I want to display a dialog, I write this line :
new PauseDialog(GameScene.this, camera, vbom).display();
The first time, it works well : the dialog is displayed, user make a choice and it's hidden.
But the 2nd time, the dialog is not hidden (after user's choice).
I used the debugger to see what's going on, and the conclusion is :
In the 2nd instance, it calls the hide() method of the first instance !
If some one can explain me what it is doing that ... Thank you.

It is because gd_visible is static. Delete the static keyword and it should work. Static fields doesn't belong to the instances but they belong to the class.

method does not override or implement a method from a supertype error

I'm trying to design an undo/redo mechanism to my Chess game.. I decided to use stack data structure which is going to build on an ArrayList.. I also want that my UndoStack and RedoStack classes should be singleton.. However i'm getting
method does not override or implement a method from a supertype
pop() in UndoStack cannot implement pop() in IStackable
return type Move is not compatible with cgas5.Move
where Move is a type-variable:
Move extends Object declared in class UndoStack
error..
Here is my IStackable interface:
package cgas5;
public interface IStackable {
abstract public Move pop();
abstract public void push(Move m);
}
and my UndoStack class
package cgas5;
import java.util.ArrayList;
public class UndoStack<Move> extends ArrayList<Move> implements IStackable {
UndoStack undoStack;
private UndoStack() {
undoStack = new UndoStack();
}
public UndoStack getUndoStack() {
if (undoStack == null) {
undoStack = new UndoStack();
}
return undoStack;
}
#Override
public Move pop() {
Move m = get(size() - 1);
remove(size() - 1);
return m;
}
#Override
public void push(Move m) {
add(m);
}
}
and if it's necessary my Move class:
package cgas5;
public class Move {
private Piece pieceToMove;
private Square currentSquare;
private Square targetSquare;
private Piece capturedPiece;
private Piece promotedPiece;
public Move(){
}
public Move(Piece pieceToMove, Square currentSquare, Square targetSquare){
this.pieceToMove = pieceToMove;
this.currentSquare = currentSquare;
this.targetSquare = targetSquare;
}
public Piece getPieceToMove() {
return pieceToMove;
}
public void setPieceToMove(Piece pieceToMove) {
this.pieceToMove = pieceToMove;
}
public Square getCurrentSquare() {
return currentSquare;
}
public void setCurrentSquare(Square currentSquare) {
this.currentSquare = currentSquare;
}
public Square getTargetSquare() {
return targetSquare;
}
public void setTargetSquare(Square targetSquare) {
this.targetSquare = targetSquare;
}
public Piece getCapturedPiece() {
return capturedPiece;
}
public void setCapturedPiece(Piece capturedPiece) {
this.capturedPiece = capturedPiece;
}
public Piece getPromotedPiece() {
return promotedPiece;
}
public void setPromotedPiece(Piece promotedPiece) {
this.promotedPiece = promotedPiece;
}
}
Thanks in advance..

This is the problem:
public class UndoStack<Move> extends ArrayList<Move>
That's using Move as a generic type parameter, whereas really you don't want a generic type at all - you just want to use Move as the type argument for ArrayList<E>. You want:
public class UndoStack extends ArrayList<Move>
That should fix the problem - although personally I'd strongly recommend using composition instead of inheritance here. (In other words, make your UndoStack type contain an ArrayList<Move> - or something similar - rather than subclassing it.)
Additionally, this is never going to work:
UndoStack undoStack;
private UndoStack() {
undoStack = new UndoStack();
}
That means that to create an UndoStack, you need to create another UndoStack... how do you expect that to happen? You'll currently get a stack overflow exception... why do you need the variable at all?