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Thread: toString method

  1. #1
    apfroggy0408 is offline Member
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    Default toString method

    I'm completely confused on how to make a working toString method. Here's what I have. This program inputs 4 variables which make fractions and add, subtract, multiply, and divide them. It's a pretty simple thing but, making the toString method and showing it is confusing me. Here it is.

    Java Code:
    /**
     * @(#)prog53.java
     *
     *
     * @author 
     * @version 1.00 2008/1/29
     */
    
    import java.util.*;
    import static java.lang.System.*;
    public class prog53 {
    
        public static void main(String args[]) 
        {
        	Fractions Tom =  new Fractions();
        	Tom.enterData();
        	Tom.add();
        	Tom.subtract();
        	Tom.multiply();
        	Tom.divide();
        }
    }
        
    class Fractions{
    double n1, d1, n2, d2;
       
        public void enterData()
        {
        	
        	Scanner input = new Scanner(System.in);
        	
        	
        	
        	
        	out.println("Enter First Numerator: ");
        	n1 = input.nextDouble();
        	out.println("Enter First Denominator");
        	d1 = input.nextDouble();
        	out.println("Enter Second Numerator: ");
        	n2 = input.nextDouble();
        	out.println("Enter Second Denominator: ");
        	d2 = input.nextDouble();
        	
        }
        
        public void add()
        {
        	double add;
        	add = ((n1/d1) + (n2/d2));
         	out.println("Adding results: " +add);
        }
        
        public void subtract()
        {
        	double sub;
        	sub = (((n1*d2) - (n2*d1)) / (d1*d2));
    		out.println("Subtracting results: " +sub);
        }
        
        public void multiply()
        {
        	double mult;
        	mult = (n1*n2) / (d1*d2);
        	out.println("Multiplying results: " +mult);
        }
        
        public void divide()
        {
        	double div;
        	div = (n1*d2) / (n2*d1);
        	out.println("Dividing results: " +div);
        }
        
        public String toString(double add, double sub, double mult, double div)
        {
        	add.toString();
        }
        
        //pg 165
    }
    Edit: The regular objects work fine when calling the methods. But again, I don't know how to make a toString method. Thanks for the help.
    Last edited by apfroggy0408; 01-30-2008 at 05:43 AM.

  2. #2
    hardwired's Avatar
    hardwired is offline Senior Member
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    Default

    The toString method is called by the jvm and returns a string that represents the state of the class instance. The member variables of this class are of interest so we return them, like this:
    Java Code:
    public String toString() {
        return getClass().getName() +
               "[n1:"+n1+", d1:"+d1+", n2:"+n2+", d2:"+d2+"]";
    }
    You use/test this inside your main method like this:
    Java Code:
    Fractions fractions = new Fractions();
    fractions.enterData();
    System.out.println("fractions = " + fractions);
    fractions.add();
    System.out.println("fractions = " + fractions);
    In the println statement the jvm calls the toString method for the "fractions" instance. If you did not provide the toString override in your Fractions class the jvm would call the toString method of its superclass (Object) which would return the class name and a hex address of the instance in memory. You can observe this by commenting–out the toString method and running your test again.

  3. #3
    babadamale is offline Member
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    there is a small mistake in your toString() method.
    public String toString(double add, double sub, double mult, double div)
    {
    add.toString(); <-- (mistake)
    }

    just typecast it into "Double" and then do whatever you want to do,like ...

    public String toString(double add, double sub, double mult, double div)
    {
    (Double)add.toString(); //now "add" is an object of the type Double
    }

  4. #4
    apfroggy0408 is offline Member
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    Wonderful, thanks a lot. I switched around the code you gave me hardwired and suited it to my needs. Here it is.

    Java Code:
    /**
     * @(#)prog53.java
     *
     *
     * @author 
     * @version 1.00 2008/1/29
     */
    
    import java.util.*;
    import static java.lang.System.*;
    public class prog53 {
    
        public static void main(String args[]) 
        {
        	Answers answers = new Answers();
    		answers.enterData();
    		answers.add();
    		answers.subtract();
    		answers.multiply();
    		answers.divide();
    		System.out.println(""+ answers);
        }
    }
        
    class Answers{
    double n1, d1, n2, d2, add, sub, mult, div;
       
        public void enterData()
        {
        	
        	Scanner input = new Scanner(System.in);
        	
        	
        	
        	
        	out.println("Enter First Numerator: ");
        	n1 = input.nextDouble();
        	out.println("Enter First Denominator");
        	d1 = input.nextDouble();
        	out.println("Enter Second Numerator: ");
        	n2 = input.nextDouble();
        	out.println("Enter Second Denominator: ");
        	d2 = input.nextDouble();
        	
    
        	out.println("");
        }
        
        public void add()
        {
        	
        	add = ((n1/d1) + (n2/d2));
         	
        }
        
        public void subtract()
        {
        	
        	sub = (((n1*d2) - (n2*d1)) / (d1*d2));
    		
        }
        
        public void multiply()
        {
        	
        	mult = (n1*n2) / (d1*d2);
        	
        }
        
        public void divide()
        {
        	
        	div = (n1*d2) / (n2*d1);
        
        }
        
        public String toString() 
        {
        
        return getClass().getName() +
               "[Addition:"+add+", Subtracting:"+sub+", Multiplying:"+mult+", Dividing:"+div+"]";
    	
    	}
        
        //pg 165
    }

  5. #5
    apfroggy0408 is offline Member
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    New question. How can i make a variable show two other variables with quotes in between. Here's what I'm trying to do.

    Java Code:
    addn = ((n1*d2) + (n2*d1));
        	addd = (d1*n2);
        	out.println(+addn);
        	out.println(+addd);
        	addfrac = addn +"/" addd;  <----- is where i'm trying to pull it
     off but it's not working
    If it doesn't make sense, tell me and I'll try to explain better.
    Last edited by apfroggy0408; 01-31-2008 at 04:03 AM.

  6. #6
    apfroggy0408 is offline Member
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    Figured it out how to show it, but it was through the toString method. If someone could still show me how to do it the way above, that would be very nice.

  7. #7
    hardwired's Avatar
    hardwired is offline Senior Member
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    Java Code:
    double addn = 25.0;
    double addd = 12.25;
    String addfrac = String.valueOf(addn) + "/" + addd;
    String s = String.format("%f/%f", addn, addd);
    System.out.println(s);

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