Understand Code

[Quizzle23]

My HW assignment is to read and understand the code below. I pretty much understand the whole thing except for a few things.
1-How is the author able to use decimal formater with out it being declaired?
2-What do the %d and %s mean? When %d first appears I see it is for the number 1,2,3,....etc to show after "Enter Password #1,2,3...etc" but how is that declaired and why and what is %s and how it is declaired and why?

import java.util.Scanner;

public class Password
{
	private final int MIN_LENGTH = 6;
	private Scanner input;
	private String password;
	
	private int count;
	private int data;
	private int valid;
	private String reportString;
	private boolean lengthOK;
	private boolean lowercaseOK;
	private boolean uppercaseOK;
	private boolean digitOK;
	
	public Password()
	{
		input = new Scanner(System.in);
		count = 0;
		data  = 0;
		valid = 0;
	}
	
	public int getNumberOfPasswords()
	{
		return count;
	}
	
	public void startPasswordChecker()
	{
		System.out.print("Ready to check your passwords? ");
		
		System.out.print("\n1Enter the number of passwords to check: ");
		count = input.nextInt();
		
		reportString = "\nHere are your results!\n";
		
		reportString += String.format("Passwords checked:\n");
	}
	
	public void inputPassword()
	{
		data++;
		
		System.out.printf("Enter password #%d: ", data);
		
		password = input.next();
		
		reportString += String.format("  [COLOR="lime"]%d. %s[/COLOR]", data, password);
	}
	
	public void checkLength()
	{
		lengthOK = (password.length() >= MIN_LENGTH);
	}
	
	public void checkLowercase()
	{
		lowercaseOK = false;
		
		for (int i = 0; i < password.length(); i++)
		{
			if (Character.isLowerCase(password.charAt(i)))
			{
				lowercaseOK = true;
				break;
			}
		}
	}
	
	public void checkUppercase()
	{
		uppercaseOK = false;
		
		for (int i = 0; i < password.length(); i++)
		{
			if (Character.isUpperCase(password.charAt(i)))
			{
				uppercaseOK = true;
				break;
			}
		}
	}
	
	public void checkDigit()
	{
		digitOK = false;
		
		for (int i = 0; i < password.length(); i++)
		{
			if (Character.isDigit(password.charAt(i)))
			{
				digitOK = true;
				break;
			}
		}
	}
	
	public void reportStat()
	{
		if (lengthOK && lowercaseOK && uppercaseOK && digitOK)
		{
			reportString += "  ** valid password";
			valid++;
		}
		
		if (!lengthOK)
			reportString += "  ** too short";
		
		if (!lowercaseOK)
			reportString += "  ** doesn't contain a lowercase letter";
			
		if (!uppercaseOK)
			reportString += "  ** doesn't contain a uppercase letter";
			
		if (!digitOK)
			reportString += "  ** doesn't contain a digit";
			
		reportString += "\n";
	}
	
	public void reportStatistics()
	{
		reportString += "Statistics:\n";
		reportString += String.format("  Number of passwords checked: [COLOR="Lime"]%d[/COLOR]\n", count);
		reportString += String.format("  Number of valid passwords:  [COLOR="lime"]%d[/COLOR](%.1f%%)\n", valid, (double)(valid*100)/count);
		reportString += String.format("  Number of invalid passwords:  [COLOR="lime"]%d[/COLOR](%.1f%%)\n", count - valid, (double)((count - valid)*100)/count);
	}
	
	public void printReport()
	{
		System.out.println(reportString);
		System.out.println("End of report");
	}
	
	public static void main(String[] args)
	{
		// instantiate a Password object
		Password password = new Password();
		
		// call startPasswordChecker
		password.startPasswordChecker();
		
		// for loop (all passwords)
		for (int i = 0; i < password.getNumberOfPasswords(); i++)
		{
			// call inputPassword method
			password.inputPassword();
			
			// call checkLength method
			password.checkLength();
			
			// call checkLowercase method
			password.checkLowercase();
			
			// call checkUppercase method
			password.checkUppercase();
			
			// call checkDigit method
			password.checkDigit();
			
			// call reportStat method
			password.reportStat();
		}
		
		// call reportStatistics method
		password.reportStatistics();
		
		// call printReport method
		password.printReport();
	}
}[LIST=1][/LIST]

Thanks

[sunde887]

I don't see where he is using a decimal formatter without declaring it, paste just the part where you see this problem.

Check out:
Formatter (Java 2 Platform SE 5.0)

You can also look into String.format.

[Quizzle23]

%d(%.1f%%)

When this prints out it looks something like this:

Percentage of Vaild Password:1 (50%)
Percentage of Invaild Password:1 (50%)

How does he do that?

[Quizzle23]

Ok so I see he used the String.format that makes sense. Is that what the %d is as well?

reportString += "Statistics:\n";
reportString += String.format(" Number of passwords checked: %d\n", count);
reportString += String.format(" Number of valid passwords: %d(%.1f%%)\n", valid, (double)(valid*100)/count);
reportString += String.format(" Number of invalid passwords: %d(%.1f%%)\n", count - valid, (double)((count - valid)*100)/count);

[sunde887]

yup, the link I used explains it pretty in depth, but there are special characters that can be used in String.format and System.out.printf().

for example if you see %d, it needs an int argument and it puts that int argument in the string. The use of String.format and printf can be very challenging to learn but they can offer a lot of power in how your strings look.

here are some examples of using printf in different ways
System.out.printf*«*java.lang*«*Java by API

but the general format is

System.out.printf("Hello there, there is %d days left", 20);

where it says %d you swap the 20 for the %d, so it would say

Hello there, there is 20 days left

You could get more complex too

System.out.printf("hello there, there are %d days in this %d day month", 20, 21);

This isn't very complex but it should print out

hello there, there are 20 days left in this 21 day month

there is an appropriate item for each type in java(bool, float, double, etc)

If you have a textbook or a decent java book check the index and see if you can find anything on this. It may also be in the Strings chapter. Thinking in Java has a pretty good bit on the use of this.

[Quizzle23]

Ok. Can you give me an easy way to do this? My assignment is to re-write the code. I will speak with my teacher about using the methods above we just have not learned them yet so I don't want to turn in something we have not went over.

[sunde887]

What's the assignment? I thought you just needed to understand the code.

[Quizzle23]

The assignment to read and understand the code and to re-write what you didn't understand in another way.

[sunde887]

Oh alright, since you didn't understand it that way you would have to hardcode

System.out.printf("hi %d", someVal);

Becomes

System.out.println("hi " + someVal);

[Quizzle23]

Super simple, thanks. I think I'll try doing it in JOptionPane.