title: how to get calculator to accept new numbers after equal sign is pressed? java
body: <p>i am doing an exercise to create a simple calculator in java. 
  i want the calculator to keep taking numbers after the equal sign is pressed. so if i press "10+10 =" the result will be 20, and if I want to press "+1 = " and the result will be 21. or if I want to subtract as well.
  my code is below. im sure the change has to be made to the "equals" portion of the code but i am unsure where/how to begin.</p>
  
  <pre><code>public int getDisplayValue()
  {
      return displayValue;
  }
  
  public void numberPressed(int number)
  {
  
      currentValue = (currentValue * 10) + number;
      displayValue = currentValue;
  
  }
  
  
  private void applyPreviousOperation()
  {
      if (previousOp == '+')
      {
          heldValue = heldValue + currentValue;
          displayValue = heldValue;
      }
          else if (previousOp == '-')
          {
              heldValue = heldValue - currentValue;
          displayValue = heldValue;
          }
  
              else {
              heldValue = currentValue;
          }
  
      }
  
  
  public void plus()
  {
     applyPreviousOperation();
     previousOp = '+'; 
     currentValue = 0;
  }
  
  
  public void minus()
  {
       applyPreviousOperation();
     previousOp = '-'; 
     currentValue = 0;
  
  
  
  
  }
  
  
  public void equals()
  {
      applyPreviousOperation();
      previousOp = ' ';
  
      currentValue = 0;
      heldValue = 0;
  }
  
  
  public void clear()
  {
      displayValue = 0;
      previousOp = ' ';
  
  }
  </code></pre>
  
  <p>}</p>