Java の wait() メソッドと sleep() メソッドの違いは何ですか?

public static void sleep(long millis) throws InterruptedException

public final void wait() throws InterruptedException<strong>
</strong>

public class ThreadTest implements Runnable {
   private int number = 10;
   public void methodOne() throws Exception {
      synchronized(this) {
         number += 50;
         System.out.println("Number in methodOne(): " + number);
      }
   }
   public void methodTwo() throws Exception {
      synchronized(this) {
         Thread.sleep(2000); // calling sleep() method 
         this.wait(1000); // calling wait() method
         number *= 75;
         System.out.println("Number in methodTwo(): " + number);
      }
   }
   public void run() {
      try {
         methodOne();
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
   public static void main(String[] args) throws Exception {
      ThreadTest threadTest = new ThreadTest();
      Thread thread = new Thread(threadTest);
      thread.start();
      threadTest.methodTwo();
   }
}

Number in methodOne(): 60
Number in methodTwo(): 4500