title: error while using isALive() or join method
body: <p>I'm trying to use isALive and join method but its throwing an error like can not find symbol....please tell me where is the error exactly in this program.
  and what is the use of join method.i know that it is a wait for threads to finish but i want in details.</p>
  
  <pre><code>class newthread1 implements Runnable {
      newthread1() {
          Thread t = new Thread(this, "FirstThread");
          System.out.println("Child Thread:" + t);
          t.start();
      }
  
      public void run() {
          System.out.println("We are in processing for 1st thread");
          int p = 1000, t = 3;
          double r = 3.5, si;
          try {
              si = (p * r * t) / 100;
              System.out.println("Simple Interest:" + si);
          } catch (ArithmeticException e) {
              System.out.println("Error:" + e);
          }
      }
  }
  
  class newthread2 implements Runnable {
  
      newthread2() {
          Thread t = new Thread(this, "SecondThread");
          System.out.println("Child Thread:" + t);
          t.start();
      }
  
      public void run() {
          try {
              System.out.println("We are in processing for 2nd thread");
              double a, r = 4.3;
              int p = 1000, n = 3;
              double temp = Math.pow((1 + r / 100), n);
              a = temp * p;
              System.out.println("Compound interest:" + a);
          } catch (ArithmeticException e) {
              System.out.println("Error:" + e);
          }
      }
  }
  
  class mainthread {
      public static void main(String args[]) {
          newthread1 t11 = new newthread1();
          new newthread2();
          boolean b = t1.t.isAlive();
          System.out.println("Thread is alive:" + b);
          t1.t.join();
      }
  }   
  </code></pre>