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Thread: String or Boolean help

  1. #1
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    Default String or Boolean help

    Ok, so i hope i am not going against any rules by posting here... i read and re-read the rules, so if i accidently break one, please let me konw.

    I did search google and stuff for this answer, but none of them post or tutorials i watched showed me what i needed.

    Ok, so i am trying to make a class (program?) that takes what the user inputs and replies to it.

    so i have

    import java.util.Scanner; //so i can use the scanner
     
    public class ScannerMain {
     
    	public static void main (String args[]){
     
    		Scanner wordscanner = new Scanner(System.in); //setting the scanner
     
    		boolean con = true; //i am just using this to keep the string repeating after they input, so they can reply to what the computer outputs
     
     
    	    while (con = true) {
    	      String answer;
    	      System.out.print("Reply:");
    	      answer = wordscanner.next(); //mostly self explanitory
     
     
    	      if (answer = "hi"){  /*here is where i get the error.... it says unable to convert String to boolean i tried changed the answer to a boolean, or copying the value of the boolean to a new variable.. but that didn't work. also, i think i may have to word the "hi" differently, what im trying to do with that: is seeing if the user had wrote hi, and if so reply with hello*/
     
     
                  System.out.println("Hello");  
    	      }else{
     
    	    	  System.out.println("I do not reconize your statement");
    	      }
    	    }
    	  }
    	}


    Again, i did try converting the string to a boolean, but i couldn't seem to get that to work.



    Code Without any comments (so you might be able to read the actual code better)

    import java.util.Scanner;
     
    public class ScannerMain {
     
    	public static void main (String args[]){
     
    		Scanner wordscanner = new Scanner(System.in);
     
    		boolean con = true;
     
     
    	    while (con = true) {
    	      String answer;
    	      System.out.print("Reply:");
    	      answer = wordscanner.next();
     
     
    	      if (answer = "hi"){
     
    	    	System.out.println("Hello");  
    	      }else{
     
    	    	  System.out.println("I do not reconize your statement");
    	      }
    	    }
    	  }
    	}

    The only error I'm getting is at the "unable to convert String to Boolean"
    Last edited by __NightWhisper__; May 17th, 2012 at 02:10 PM.


  2. #2
    Super Moderator Sean4u's Avatar
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    Default Re: String or Boolean help

    one = is 'assignment', it means copy the value on the right to the variable on the left. The type of an 'x = y' expression is the type of x, so String x = "a letter y" is an expression with a String type.
    two =, like == is 'test for equality', compare the left side to the right side and return boolean true if they're the same, boolean false otherwise. It doesn't matter what type x and y are in x == y, the type of the expression is boolean.
    If statements are if ([boolean_expression]) - no other type of expression is allowed.

  3. #3
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    Default Re: String or Boolean help

    Quote Originally Posted by Sean4u View Post
    one = is 'assignment', it means copy the value on the right to the variable on the left. The type of an 'x = y' expression is the type of x, so String x = "a letter y" is an expression with a String type.
    two =, like == is 'test for equality', compare the left side to the right side and return boolean true if they're the same, boolean false otherwise. It doesn't matter what type x and y are in x == y, the type of the expression is boolean.
    If statements are if ([boolean_expression]) - no other type of expression is allowed.
    i am ashamed, i have watched so many tutorials, and actually used that before (the ==) my brain was out of it, thank you

    ok, now i don't know if this is the way i worded the code or not, but no-matter what i type, it still goes with the second argument (I do not reconize that statement)

    Here is my updated code:

    import java.util.Scanner;
     
    public class ScannerMain {
     
    	public static void main (String args[]){
     
    		Scanner wordscanner = new Scanner(System.in);
     
    		boolean con = true;
     
     
    	    while (con = true) {
    	      String answer;
    	      System.out.print("Reply:");
    	      answer = wordscanner.next();
     
     
    	      if (answer == "hi"){
     
    	    	System.out.println("Hello");  
    	      }else{
     
    	    	  System.out.println("I do not reconize your statement");
    	      }
    	    }
    	  }
    	}


    Thanks for your help!!

  4. #4
    Super Moderator Sean4u's Avatar
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    Default Re: String or Boolean help

    == compares the left hand side with the right hand side. answer's 'type' is a String reference - it's a reference that you assigned to a (reference to a) String object returned from your Scanner's next() method. "hi" is another, completely separate String object which has its own reference. The two references are not the same. '==' is doing the very shallowest of comparisons between the two reference types. It is asking "is the left hand side referring to the same object that the right hand side is referring to?". If you want to do something deeper (like compare the content of the two objects to see if they hold the same sequence of characters), you'll need to use the equals() method. Read the API documentation for Object.equals and String.equals

  5. #5
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    Default Re: String or Boolean help

    Keep in mind that the == operator will only work for primitive data types (char, int, double, float...ect.). When comparing Objects, in this case Strings, you should use the equals() method provided by the Object class.

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