why aren't the x's printed when PrintNum reaches 50?

PrintChar.java

package je3.thread;

/**
 * Created by IDEA on 01/02/15.
 */
public class PrintChar implements Runnable {

    private char charToPrint;
    private int times;

    public PrintChar(char c, int t) {
        charToPrint = c;
        times = t;
    }

    public PrintChar(char b) {
        this(b, 100);
    }

    @Override
    public void run() {
        for(int i = 0; i < times; i++) {
            System.out.print(charToPrint);
        }
    }
}

PrintNum.java

package je3.thread;

/**
 * Created by IDEA on 01/02/15.
 */
public class PrintNum implements Runnable {

    private int lastNum;

    public PrintNum(int n) {
        lastNum = n;
    }

    @Override
    public void run() {
        Thread thread4 = new Thread(
                new PrintChar('x', 40)
        );

        try {
            for (int i = 1; i <= lastNum; i++) {
                System.out.print(i + " ");
                if(i == 50) {
                    thread4.join();
                }
            }
        }
        catch (InterruptedException e) {}
    }
}