Thread: What's Wrong With My Code?

Please help me, I cannot find the error in the following code. Boolean always returs true in the following program.

class time
{   
    int hh, mm, ss;
    public time()
    {
        hh = 0;
        mm = 0;
        ss = 0;
    }
    public time(int h, int m, int s)
    {
        hh = h;
        mm = m;
        ss = s;
    }
    public boolean validate()
    {
        boolean valid = false;       
        if((hh>=0 && hh<=23)||(mm>=0 && mm<=59)||(ss>=0 && ss<=59))
        valid=true;
        return valid;
    }
    public void display()
    {
        if(hh>12) 
        hh=hh-12;
        System.out.println("Your time is: "+ hh+":"+ mm +":"+ ss);
    }
    public static void main(String args[])    
    {
        time ob = new time(20,55,30);
        if (ob.validate()==true)
        ob.display();
        else
        System.out.println("Invalid format");
    }
}

Thank you very much for helping me. now i have only one problem on my program. If i enter time >23, it should display "Invalid Format". but its is showing the time subtracting 12.
Here is the final code

class Time
{   
    int hh, mm, ss;
    public Time()
    {
        hh = 0;
        mm = 0;
        ss = 0;
    }
    public Time(int h, int m, int s)
    {
        hh = h;
        mm = m;
        ss = s;
    }
public boolean validate()
    {
        if((hh>=0 && hh<=23) && (mm>=0 && mm<=59) && (ss>=0 && ss<=59))
                return true;
        else
                return false;
    }
    public void display()
    {
        if(hh>12) 
        hh=hh-12;
        Time ob = new Time(20,55,30);
        if (ob.validate())
        System.out.println("Your time is: "+ hh+":"+ mm +":"+ ss);
        else
        System.out.println("Invalid format");
    }
 
}

Originally Posted by TopdeK

Classes need to begin with a Capital letter. So in this case, "time" should be "Time". Change all the mentions of "time" to "Time" and all will be fine. Also I noticed that your validate() method is not exactly accurate. So long as ONLY ONE of the three conditions is satisfied, it will work. You need ALL THREE to be satisfied to be a correct time:

For your validate() method, replace the "||" with "&&":

    public boolean validate()
    {
        if((hh>=0 && hh<=23) && (mm>=0 && mm<=59) && (ss>=0 && ss<=59))
                return true;
        else
                return false;
    }

Following on from that, in the main program, you don't have to say if(ob.validate() == true)...you could just say if(ob.validate()).

Thank you for pointing out the problems. I would be more greatful if you make the necessary correction on my codes as I am very new in Java programs.

Originally Posted by helloworld922

if(hh>12) 
                hh=hh-12;
        Time ob = new Time(20,55,30);
        if (ob.validate())

You're automatically subtracting 12 from hh no matter if the format is valid or not. Secondly, you're storing that result back into hh. you should instead either store that result to a temporary variable, move the subtraction to after you've checked that you have a valid time, or remove it all together and have your program display it out in military time (since display() doesn't print out if it's AM or PM anyways).

Lastly, creating ob is useless since it has no bearing on the current object. Calling validate on that object will always be true since it's always going to be a valid time. Instead, call validate on your current time object.

i have made my code as follows... now the question is how can i display time as 12 hour format?

public void display()
    {
//        if(hh>12) 
//        hh=hh-12;
//        Time ob = new Time();
//        if (ob.validate())
if(this.validate()) // using the this keyword.
        System.out.println("Your time is: "+ hh+":"+ mm +":"+ ss);
        else
        System.out.println("Invalid format");
    }
 
}

Originally Posted by helloworld922

Yep. The name can start with any letter (upper or lower case), an underscore, or some currency symbols (such as the british pound symbol or dollar symbol). Actually, any valid name for a variable/method is automatically a valid name for a class (and vise-versa). Same goes for interfaces, enums, etc. Of course, these names probably shouldn't be used because they can get extremely confusing.

class _
{
    public static void main(String[] $)
    {
        System.out.println($[0]);
    }
}

I try not to provide the full solution because I believe you won't learn how to fix your code if I just dump the code. See if you can't take the description I gave and modify your code accordingly.

To call a member method of the same class, you can leave of all object quantifiers, or use the "this" keyword:

if(this.validate()) // using the this keyword.
{
    // this time is valid. do stuff in here
}

Originally Posted by TopdeK

Really? My lecturer needs to get his facts right then. Thanks for the clarity

Someone who knows more than I can correct me, but classes do not need to begin with a capital letter in the sense that is a compile-time or run-time error if they don't. However, it is a coding convention that they do, because it makes all <ClassName> type readily distinguishable from instance variables.

Sorry! i cannot apply the tecnique in my program. please help me

Originally Posted by helloworld922

You can display in a 12 hour format by creating a temporary hour variable, and a temporary string variable to hold "am" or "pm". This variable would hold the value of hh if hh is less than or equal to 12 and the string should contain "am". If hh is greater than 12, the temporary hour variable should hold hh-12 and the string should contain "pm". If hh is 0, the temporary hour variable should hold 12 and the string should contain "am".

Then, your output code would print out:

int tempHour = 0;
String period = null; // either "am" or "pm"
// TODO: initialize tempHour and period according to my descriptions
System.out.println("Your time is: "+ tempHour +":"+ mm +":"+ ss + period);

I am feeling shy now!
I changed my code as follows... but its incorrect. please help me

public void display()
    {
        if(this.validate()) // using the this keyword.
        {
            if(hh>12)
            {
            hh=hh-12;
        }
        System.out.println("Your time is: "+ hh+":"+ mm +":"+ ss);
    }
        else
        System.out.println("Invalid format");
    }

Originally Posted by helloworld922

What part are you having trouble with?

You can perform multiple statements in one if statement by using brackets.

if(condition== true)
{ // execute all statements in here if condition is true, otherwise do none of them
    System.out.println("doing statement 1");
    System.out.println("doing statement 2");
}

Thank you Very Much. My problem is now solved.

Originally Posted by helloworld922

Sorry, I'm not trying to intimidate you, but I do want you to think.

Ok, so first you have your if statement which checks to see if the time is valid:

if(this.validate())
{
    // we have a valid time, do stuff in here
}
else
{
    // invalid time
    System.out.println("invalid time");
}

Now that you have a valid time, we want to create a local temporary variable we can modify without changing hh of the object. We also want a string to hold if we're in the morning or afternoon. For the sake of simplicity, let's assume it's am.

int temporaryHH = hh;
String period = "am"; // this is an assumption

After assuming it's am, we need to validate that assumption. How do we know if it's am? If temporaryHH is before noon (smaller than 12). Otherwise, it's pm. If it's pm, temporaryHH needs to be decreased by 12.

if(temporaryHH >= 12)
{
    // pm
    period = "pm";
    temporaryHH = temporaryHH - 12;
}

The last thing to check is if temporaryHH is 0. What does it mean to be 0 am or 0 pm? That's the equivalent of 12 am or 12 pm. To see if you understand this, I'd like you to see if you can figure out how to accomplish this using the above code (remember to operate on temporaryHH, not hh).

Your final code should look something like this:

if(this.validate())
{
    // we have a valid time
    int temporaryHH = hh;
    String period = "am"; // assume we're am
    if(temporaryHH >= 12)
    {
        // actually in pm
        period = "pm";
        temporaryHH = temporaryHH - 12;
    }
 
    // TODO: what code should go here to fix if temporaryHH is 0?
 
    // print out the valid time
    System.out.println("Your time is: "+ temporaryHH +":"+ mm +":"+ ss + period);
}
else
{
    // invalid time
    System.out.println("invalid time");
}

If you use brackets like I did (indent in on each open bracket, indent out on each close bracket) you can easily tell if you're missing a bracket, as well as see what code belongs to which condition.