I am rather inexperienced with Java and multi-threading so maybe you guys can help. I am having trouble printing out a series of numbers and letters in a TextArea box when I multi-thread. This is my code:
public class MultiThread extends Application {
static TextArea outputArea = new TextArea();
@Override
public void start(Stage primaryStage) throws Exception {
outputArea.setWrapText(true);
Runnable printA = new PrintChar('a', 100);
Runnable printB = new PrintChar('b', 100);
Runnable print100 = new PrintNum(100);
// Create threads
Thread thread1 = new Thread(printA);
Thread thread2 = new Thread(printB);
Thread thread3 = new Thread(print100);
thread1.start();
thread2.start();
thread3.start();
Scene scene = new Scene(outputArea, 250, 130);
primaryStage.setTitle("Concurrent Output");
primaryStage.setScene(scene);
primaryStage.show();}
public static void main(String[] args) {
launch(args);
}
}
class PrintChar extends MultiThread implements Runnable {
private char charToPrint; // The character to print
private int times; // The times to repeat
public PrintChar(char c, int t) {
charToPrint = c;
times = t;
}
@Override
public void run() {
for (int i = 0; i < times; i++) {
outputArea.appendText(charToPrint + "");
}
}
}
class PrintNum extends MultiThread implements Runnable {
private int lastNum;
private char charToPrint;
public PrintNum(int n) {
lastNum = n;
}
@Override
public void run() {
for (int i = 1; i <= lastNum; i++) {
outputArea.appendText(i + "");
}
}
}
When I run the code, the threads do not usually print out all of what they are supposed to. For example, 'print100' does not always print to number 100 like it's supposed to. I also get random results and I never get the same output nor errors each time.
Exception in thread "Thread-6" Exception in thread "Thread-4" java.lang.IndexOutOfBoundsException
at javafx.scene.control.TextInputControl.getText(TextInputControl.java:451)
at javafx.scene.control.TextInputControl.updateContent(TextInputControl.java:564)
at javafx.scene.control.TextInputControl.replaceText(TextInputControl.java:548)
at javafx.scene.control.TextInputControl.insertText(TextInputControl.java:473)
at javafx.scene.control.TextInputControl.appendText(TextInputControl.java:463)
at threader.PrintChar.run(Threader.java:53)
at java.lang.Thread.run(Thread.java:748)
java.lang.IndexOutOfBoundsException
at javafx.scene.control.TextInputControl.getText(TextInputControl.java:451)
at javafx.scene.control.TextInputControl.updateContent(TextInputControl.java:555)
at javafx.scene.control.TextInputControl.replaceText(TextInputControl.java:548)
at javafx.scene.control.TextInputControl.insertText(TextInputControl.java:473)
at javafx.scene.control.TextInputControl.appendText(TextInputControl.java:463)
at threader.PrintNum.run(Threader.java:71)
at java.lang.Thread.run(Thread.java:748)
I am almost positive it is a problem with synchronizing the multiple threads in the code, but I can't seem to figure out how to do so for this specific code.
The TextArea implementation is obviously not thread safe, so you should make sure that the current thread is not interupted while calling methods on your TextArea object. You can do this for example by synchronizing on the TextArea object itself:
synchronized (outputArea) {
outputArea.appendText(charToPrint + "");
}