How To Make Sure Only One Particular Type Of Instance Is Open At A Time
Feb 23, 2015
This isn't asking to make a Singleton, where I want only one type of a type of window period.
It's not where I want only one instance of the program itself open at a time. It's more along the lines of, though I don't care if there is more than one Microsoft Word open at the same time, I don't want more than one instance of blablabla.docx to be open at once.
In other words, I'd need to scan my system or my list of open windows of a particular type to make sure that no two ones where equals is true will match up.
I was going to do it to associate it with a particular name with a window (it's sort of an addressbook, though not quite.) I'd use a JFrame subclass to make these windows that have a name go with them. For now, unless I find the great need for this project that there might be someone with the exact same name around here, I'm going to use equals() with name on this. I can type cast and whatnot.
However, how do I get to know what windows are open at once so I can check all my list of open windows, and I'd prefer to check only ones of certain types, though I may have to check them all indirectly perhaps, before I check the names.
I'm wondering is it a getChildren() of the main window or something else? How do I know what all of my open windows are?
I'd prefer to have to check as few as possible and not have to check unnecessary ones.
As for the structure of my thing that would click that would open the new window, I'm not sure yet. I'm almost leaning JLabel, though it's a bit less sophisticated, as it might be more difficult to add to a JList (maybe I"m wrong on thinking on that. It's been a little while since I last worked with JLists.)
(I think I can set list data, but the problem is, even using an ArrayList, it only takes an array for this as a param and ArrayList returns an Array of type Object, which means a lot of pesky type casting every time just to add or remove a name.)
It does have Vector, but I thought Vector was being phased out.
Anyway, without having too much code given, as I'm not sure how I'll set this up yet, how do you get access to all of the windows being opened to be able to check them for certain traits?
Is there anyway to iterate an enum type without an instance. As some context, consider the following code:
Java Code: public interface GenericChecker { public bool isValid(String str); } mh_sh_highlight_all('java'); Java Code: public class EnumChecker<T extends Enum<T> > extends GenericChecker { private Class<T> enumType; //No instance
[code]....
toString method of the enum types has been overridden so that it returns the name assigned to the enum rather than the enum name itself. For example an enum might be SOME_ENUM("Assigned name"), therefore toString returns "Assigned name" rather than "SOME_ENUM". The idea is that a field from a table can be handed to the isValid(String) function on the GenericChecker base, and the derived class will then check to see if the field matches valid data as far as it is concerned.Thus, I can create a whole bunch of checkers easliy:
public void randomCreate(ParentObject obj){ int x = random(0-4); //pseudo int y = random(0-4); //pseudo create new ParentObj(x,y); }
ParentObject is actually abstract, so you would only ever pass one of its children objects to it, and a child object of that type would be created. It seems like there should be a way to pass a type, rather than an object, and then create an instance later down, but I don't know if that is actually possible, or if it is poor programming style.
So I'm fairly new to java and have been learning game development. I've come across this error message on my StartingClass.java coding. Here is the Coding
@Override public void start() { bg1 = new Background(0,0); // This line is giving me the error!!!!!!!!!!! bg2 = new Background(2160, 0); hb = new Heliboy(340, 360); hb2 = new Heliboy(700, 360); robot = new Robot();
Thread thread = new Thread(this); thread.start();
The error reads "No enclosing instance of type BackGround is accessible. Must qualify the allocation with an enclosing instance of type BackGround (e.g. x.new A() where x is an instance of BackGround)." Now I have seven classes in my in my games src folder and none of them but the StartingClass.java has the error. Once again I'm fairly new to java and have not benn able to fix it.
These are the classes{
BackGround.java Enemy.java Heliboy.java package-info.java Projectile.java Robot.java StartingClass.java ( errors in this class ) }
I am trying to make a generic method that will replace the data type T with those number types usable with a Scanner object. However, whenever I try to compile, I get errors saying that a Byte/Integer/Double etc are found when only a type T is allowed. This is the beginning of my method. I can;t understand what is wrong with it.
Java Code:
public <T extends Number> T nextRanged(T lowerBound, T upperBound, boolean inclusive, String errorMessage){ // Holds program execution until user inputs a numeric value between the bounds. Prevents all other input without exception. // Output data type determined by the type of the bounds. T input = null; try{ if(input instanceof Byte){ input = new Byte(internalScanner.nextByte());
[Code] ....
The purpose of the method, in the end, will be to provide the nextXXX() functionality of a Scanner object but with built in validation procedures. I could easily do this by making a nextIntRanged(), nextDoubleRanged() etc methods, but this seems wasteful to me.
I meant "incompatible type errors"!
Error example:
ValidatedScanner.java:57: error: incompatible types input = new Byte(internalScanner.nextByte()); ^ required: T found: Byte
where T is a type-variable:
T extends Number declared in method <T>nextRanged(T,T,boolean,String)
I already done a lot of work(user lists, server logging, private messages), but im there is few thing i still dont know how to really implement and, of course my current program is far from beign decent, so i decided to start asking questions(so far i was just experimenting just using knowledge from book and some info found on Java API).
1. How can i make JTextField to scroll down each time new message received and log is already full? i mean visible part of it, so you don't need to scroll it yourself...
2. Why sequencer doesn't play MIDI if it is launched not by main thread?
3. What is good way to do user list with avatars? atm, i'm using regular JList and listening to selected values to open dialogs.
4. What is a good ways to implement sounds in application, other than MIDI? i know that i should just google it, but anyway.
You can check my source code for it by link. Chat client:URL...
How to make shapes move at same time when user enter up it should move up. It works for rectangle but i don't know how to move the others like that. (btw i am new to java). How can i do that?
I have a code in which I am reading input from System.in and Destination is some where else
Here is my code
File file=new File("D:/output.txt"); OutputStream os=new java.io.FileOutputStream(file); Scanner scanner=new Scanner(System.in); System.out.println("Enter Data to write on File"); String text=scanner.nextLine(); int c=Integer.parseInt(text); int a; while((a=c.read())!=-1) os.write(a); System.out.println("File Written is Successful");
In the line while((a=c.read())!=-1)
a compile time error is shown "cannot invoke read on primitive data type int"
Ok, so I have to make a program that tells the user to type a sentence and at the end of the sentence a "." must be put to end the program. If a "." period is not entered, it must re-prompt the user to enter a period. On top of all this, the program has to count the number of letters in the sentence. I cant seem to get the while loop working and I cant find anywhere how to make a counter count the number of letters.
import java.io.*; class Sentence //The purpose of this program is to
I am trying to run a class with a client code and I get the following error
The method add(TimeSpan) is undefined for the type TEST
Why i get this error?
package timespan; // Represents a time span of hours and minutes elapsed. // Class invariant: minutes < 60 public class TimeSpan { private int hours; private int minutes;
I use this code in Restlet Representation. I try to get the value from the Request API. But I am facing the problem as "Cannot make a static reference to the non-static method getQuery() from the type Resource".
I am writing the following program in Java SE 7. It throwing "Cannot make a static reference to the non-static type String" . However if I write parameterised String inside main method as java.lang.String[] args, it compiles fine.
class MainClass<String> { <T> MainClass(T t) { System.out.println(t.getClass().getName()); } public static void main(String[] args) { System.out.println("asdasd"); new MainClass<>(""); } }
I mean following programs compile fine in Java SE 7 :
class MainClass<String> { <T> MainClass(T t) { System.out.println(t.getClass().getName()); } public static void main(java.lang.String[] args) { System.out.println("asdasd"); new MainClass<>(""); } }
I am working on an assignment that I can't seem to figure out the final part to. The program takes in course data such as the time the class starts and how long it lasts. The time is in military time (0000 - 2400)
I need the output time to be the time the class started, plus the length of the class, and displayed in military time.
I can't for the life of me figure out how to do this. I have gotten a program that works for this time and minutes, and displays the correct 1020. But when I change the information to say
Start time: 0700 Length = 90 minutes
I get:
Endtime = 90
90 is technically correct, the way the formula is setup, but I need it to display 0900 not 90.
Here is the code that I have. Be easy, I'm still learning, and this is just the file I created to get the formula to work. Also, the verbose in here is just for my own debugging to make sure values should be what I'm expecting them to be.
public class calc { public static void main(String[] args) { double hours, minutes, length; double temp; int time = 2400; hours = time / 100; System.out.println("Hours are: " + hours);
If you have final int i = 1; short s = 1; switch(s) { case i: System.out.println(i); }
it runs fine. Note that the switch expression is of type short (2 bytes) and the case constant is of type int (4 bytes).My question is: Is the type irrelevant as long as the value is within the boundaries of the type of the switch expression?I have the feeling that this is true since:
byte b = 127; final int i = 127; switch(b) { case i: System.out.println(i); }
This runs fine again, but if I change the literal assigned to i to 128, which is out of range for type byte, then the compiler complains.Is it true that in the first example the short variable and in the second example the byte variable (the switch expressions) are first implicitly converted to an int and then compared with the case constants?
Got a problem with generics, which I'm still pretty new at. Here's a program that compiles fine:
import java.util.ArrayList; import javax.swing.JComponent; public class Experiments { public static void main(String[] args) { ListHolder holder = new ListHolder();
[Code] ....
It's useless, but it compiles. If I change Line 14, however, to add a generic type parameter to the ListHolder class, Line 10 no longer compiles:
import java.util.ArrayList; import javax.swing.JComponent; public class Experiments { public static void main(String[] args) { ListHolder holder = new ListHolder();
[Code] ....
I get this error:
Uncompilable source code - incompatible types: java.lang.Object cannot be converted to javax.swing.JComponent at experiments.Experiments.main(Experiments.java:10)
Apparently, the introduction of the type parameter leaves the compiler thinking that aList is of type Object. I can cast it, like this:
JComponent c = ((ArrayList<JComponent>)holder.aList).iterator().next();
That makes the compiler happy, but why is it necessary? How does adding the (unused) type parameter to the ListHolder class end up making the compiler think the aList member of an instance of ListHolder is of type Object?
How do i make the 'date' column show only the date and 'timeIn' and 'timeOut' column only show the time. In my database table my 'date' column is a date type and 'timeIn' and 'timeOut' column is time.
I have two classes. time_runner is used for testing my code.
This is what I'm using to test my code:
class time_runner { public static void main(String str[]) throws IOException { Time time1 = new Time(14, 56); System.out.println("time1: " + time1); System.out.println("convert time1 to standard time: " + time1.convert()); System.out.println("time1: " + time1); System.out.print("increment time1 five times: "); time1.increment();
[code]....
The two constructors are "Time()", which is the default constructor that sets the time to 1200, and "Time(int h, int m)" Which says If h is between 1 and 23 inclusive, set the hour to h. Otherwise, set the hour to 0. If m is between 0 and 59 inclusive, set the minutes to m. Otherwise, set the minutes to 0. Those are my two constructors that I pretty much have down. The three methods however I'm having trouble with. The "String toString()" Returns the time as a String of length 4. The "String convert()" Returns the time as a String converted from military time to standard time. The "void increment()" Advances the time by one minute.
public class Time { private int hour; private int minute; public Time(int h, int m) { if(h > 1 && h < 23) hour = h;
I'm trying to parse and compare the content of a zip file. However I'm stuck at what SHOULD be a very simple problem, however I can't seem to find a solution. I have done the following:
ZipInputStream zin1 = new ZipInputStream(fin); ZipEntry ze1 = null; fin2 = new FileInputStream(fileName2); ZipInputStream zin2 = new ZipInputStream(fin2); ZipEntry ze2 = null; //fin.close(); ze1 = zin1.getNextEntry(); ze2 = zin2.getNextEntry();
Which gives me the first entry of each zipfile as a ZipEntry type object. I have tried getting the path of the file (inside the zip file) and using this to create a File type object. This does not seem to work though I get:
Exception in thread "main" java.io.FileNotFoundException: My DocumentsmetadatacoreProperties.xml (The system cannot find the file specified) at java.io.FileInputStream.open(Native Method) at java.io.FileInputStream.<init>(Unknown Source) at java.io.FileReader.<init>(Unknown Source)
And this is because I get a null return from trying to create the File file1 = new File(correctLocation);
I guess I cannot access the file inside a zip file this way. So my question is how can I make a ZipEntry type object into a File type object?
The objective of the code is to add new records based on existing records with a partial change to the key. I'm getting "type of the expression must be an array type but it resolved to DstidArray" on dsTidRecTbl[i]
String stMajor = request.getParameter("stMajorVersion"); String stMinor = request.getParameter("stMinorVersion"); String stPatch = request.getParameter("stPatchVersion"); StringBuffer stKeySB = new StringBuffer(stMajor+stMinor+stPatch); String stKey = new String(stKeySB.toString()); DstidArray dsTidRecTbl = new DstidArray(stKey); request.setAttribute("dsTidRecTbl", dsTidRecTbl);
