if statements and null values

chris1012 · December 31st, 2007, 09:18 AM

hey guys i know am a complete pain but am trying to acomplish something here that is a little tricky

basically am having trouble distinguishing how to work out this line of code my code is shown before what am trying to do is if the object lw function = a null value it goes to a joptionpane message box i've done it so far just without a null value for example when the joption message button cancel is clicked the lwfunction varaible is defined as so on ideally i would like the code to work with an ifstatement but i've tried that and it messes up and say incompatible types when the compiler is run.

    public void lite()
    {
    for (int liteweight=0; liteweight<3; liteweight++)
        {
    lwfunction = JOptionPane.showInputDialog(null, "What Weights the most in the?", "Heaviest Weight", JOptionPane.QUESTION_MESSAGE,null, new String[]{"Weight +5 years","Weight +3 years","Initial Weight"},"");

    if (lwfunction.equals("Weight +5 years"))
        {
        lwfive();
        }
        else if (lwfunction.equals("Weight +3 years"))
                {
                lwthree();
                }
                else if (lwfunction.equals("Initial Weight"))
                {
                    liw();
                }
        }
    Question();
    }

in opposite world i love programming

ciderpunx · January 3rd, 2008, 09:10 AM

Remember that null is a primitive in java. Check for that using an ==

Code:

  // Nb I changed the function calls to print statements
  // to save having to rewrite your functions!
  public void lite(JFrame parent) {
    for (int liteweight=0; liteweight<3; liteweight++) { 
      // Create lwfunction object
      Object lwfunction = JOptionPane.showInputDialog(parent, 
          "What Weights the most inthe?", "Heaviest Weight",
          JOptionPane.QUESTION_MESSAGE,null, 
          new String[]{"Weight +5 years","Weight +3 years",
            "Initial Weight"},""
      );  

      // If the Object is null/we had cancel pressed. Null is
      // a primitive in java so we compare using == null 
      if (lwfunction == null)  { // if its null
        System.out.println("Got null/Cancel pressed");
        // return from our function
        return;
      }   

      // We now know our object is not null.
      if (lwfunction.equals("Weight +5 years")) {
        System.out.println("lwfive()"); 
      }   
      else if (lwfunction.equals("Weight +3 years")) {
        System.out.println("lwthree()"); 
      }   
      else if (lwfunction.equals("Initial Weight")) {
        System.out.println("liw()") ; 
      }   
    }   
    System.out.println("Question()"); 
  }

--
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