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  1. #1
    veloDMC is offline Member
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    Aug 2011
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    Default Need help with an illogical logical statement

    I need some help to understand why a logical statement is not working as I expect it should.
    I am very new to Java and am creating a simple program that uses a client and server class. The code below is from the server class.

    The client class asks the user to input a studentís name and test scores. The server class validates the user input, amongst other things.

    To test the validateData() method, I input an empty string as a studentís name when the client class asked me to. (ie.simply hit the enter key).

    However the logical 'while' statement below never evaluates as true and always displays the negative condition action (ie ďThis is the else statementĒ). I have also tried using an if-else configuration but the same thing happens.

    I tried reversing the problem and using while (name != "") and entering a name eg Bob. In this case the statement will evaluate as true and return the positive condition action and print ďThe studentís name has not been entered.Ē

    This problem is tying me up in knots and I donít know how to resolve it. I appreciate your help.
    Java Code:
    public class Student {
    	// Manage a student's name and three test scores.
    	//Instance variables
    	//Each student object has a name and three test scores
    	private String name;	//Student name
    	private int test1;		//score on test 1
    	private int test2;		//score on test 2
    	private int test3;		//score on test 3
    public void validateData(){
    		//validate student data
    while (name == ""){
    //this line is not working and I don't know why.
    //I think 'name' has a value even if it is "" and so always 
    //returns as a false value and triggers the else statement
    		System.out.println("The student's name has not been entered.");
    		System.out.println("This is the else statement.");
    //the else statement is displaying even if i put an empty string as a name
    Last edited by pbrockway2; 08-31-2011 at 01:02 PM. Reason: code tags added

  2. #2
    pbrockway2 is offline Moderator
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    Feb 2009
    New Zealand
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    Hi, welcome to the forums.

    It helps everyone if you use code tags when posting code: put [code] at the start of the code and [/code] at the end. That way the code will be readable when it appears here.


    Use the String method equals() to compare strings. == tests for identity whereas you are merely trying to see if two strings are made up of the same sequence of characters which is what equals() tests for.

  3. #3
    Norm's Avatar
    Norm is offline Moderator
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    Jun 2008
    Eastern Florida
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    Java Code:
    while (name == ""){
    Don't use the == operator when comparing the contents of String objects. Use the equals method or for this test you could use the length method.

  4. #4
    Junky's Avatar
    Junky is offline Grand Poobah
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    Jan 2011
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    Is it too late to mention DOUBLE POSTED over at the Ranch?

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