Thread: Looping Question (newbie)

Hello, I am new in this forum, hope you guys can help me with my problem.

Our professor gave us a take home quiz and I don't know what to do anymore after several attempts in doing the program. I have done 3 programs already and all of them was gone crazy.

Would you guys mind help me in the program.

OUTPUT:

Enter a letter: J
Enter a letter: A
Enter a letter: V
Enter a letter: E
Enter a letter: C
Enter a letter: J
Enter a letter: A
Enter a letter: V
Enter a letter: A

J-A-V-A formed!

As you can see the word "JAVA" is formed from the 6th line to the last.

The program goes like this "It will continue to loop as long as the word 'JAVA' is not formed" and when the word 'JAVA' is formed it will display "J-A-V-A formed!".

Thanks a lot!

The program needs to keep reading until it gets a "J"
Then it MUST read an "A"
if not an A it starts over
Continue getting the next two letters: V & A using the same kind of logic

@aussiemcgr
In our situation, it will only stop if the word JAVA is formed.

indexOf(String value) - I don't know this function yet because I think it is on more complex programming and I think that our class were only at the basic.

Would you mind provide me a source code for this program, then I'll try to analyze it so I can explain it to my classmates.

@Norm
You got the logic sir.

You got the logic

Is that a question or a statement?

I thought I gave you a start on the logic. You'll need to fill it in.

@aussiemcgr
In our situation, it will only stop if the word JAVA is formed.

indexOf(String value) - I don't know this function yet because I think it is on more complex programming and I think that our class were only at the basic.

Would you mind provide me a source code for this program, then I'll try to analyze it so I can explain it to my classmates.

Sure, but please dont use this as your quiz answer...

I'll show you how it works. Very simple. I'm going to assume you are using Scanner (despite how I hate it).

import java.util.Scanner;
 
public class Test
{
 
    public static void main(String[] arguments)
    {
		Scanner sc = new Scanner(System.in);
		String temp = "";
		while(true)
		{
			System.out.print("Enter a letter: ");
			String value = sc.nextLine();
			temp+=value;
			if(temp.indexOf("JAVA")!=-1)
			{
				System.out.println("J-A-V-A formed!");
				break;
			}
		}
   	}
}

I've actually never used that version of indexOf before (with a string sent to it), its kind of cool how it works.

@Norm
It is a statement.

Hmm, I'll try to fill it.

Enter a letter: J
Enter a letter: A
Enter a letter: C

First, I enter "J" followed by "A" which is to formed JAVA but I enter a "C" on the third which will destroy the sequence of JAVA so we need to start all over again until we formed a JAVA word.

Enter a letter: J
Enter a letter: A
Enter a letter: V
Enter a letter: A

So the output will become like this:

Enter a letter: J
Enter a letter: A
Enter a letter: C
Enter a letter: J
Enter a letter: A
Enter a letter: V
Enter a letter: A

Originally Posted by aussiemcgr

Sure, but please dont use this as your quiz answer...

I'll show you how it works. Very simple. I'm going to assume you are using Scanner (despite how I hate it).

import java.util.Scanner;
 
public class Test
{
 
    public static void main(String[] arguments)
    {
		Scanner sc = new Scanner(System.in);
		String temp = "";
		while(true)
		{
			System.out.print("Enter a letter: ");
			String value = sc.nextLine();
			temp+=value;
			if(temp.indexOf("JAVA")!=-1)
			{
				System.out.println("J-A-V-A formed!");
				break;
			}
		}
   	}
}

I've actually never used that version of indexOf before (with a string sent to it), its kind of cool how it works.

I'm not familiar with Scanner but I think it is the same as BufferedReader?

Originally Posted by aussiemcgr

Actually, temp+=value; is the same as saying temp = temp+value. Since we are doing it with Strings, we are saying add value to the end of temp. But, we never clear temp for this example so it just keeps adding on the to the string, which is fine since we are using the indexOf method. However, doing it the other way, you want to store the strings in their own individual strings because you need to erase the previous, shift the values down, and read the new one in.

So, as the loop goes, here is what temp equals:
temp = J
temp = JA
temp = JAV
temp = JAVE
temp = JAVEC
temp = JAVECJ
temp = JAVECJA
temp = JAVECJAV
temp = JAVECJAVA

As for the -1. String.indexOf(String value) returns an int of the index of the start of the word give in value. If it cannot find the value, it returns -1. So, by saying: if(temp.indexOf("JAVA")!=-1) you are checking to see if String.indexOf(String value) found value in the string. If it does find value, it will return a value other than -1. So we only want to stop the loop when String.indexOf(String value) returns something other than -1.

If that doesnt make sense, here is the API entry for this method in the String class. The API is your BEST FRIEND, you will be referencing it every time you program to look for methods and parameters. Whenever I code, I always have the web browser open to the API.

That clears it. I thought that the use of the indexOf("JAVA")!=-1 is to scan every 4- letter word from the start and when it does find the word "JAVA", there will be some values that is not equal to -1 that makes the if-statement satisfied and display the "J-A-V-A formed!".

Thank you for explaining it to me very well, I learned a lot from you.

the -1 in the if statement.

Read the API doc for the indexOf() method to see what values it returns.

Originally Posted by xdrechsler

That clears it. I thought that the use of the indexOf("JAVA")!=-1 is to scan every 4- letter word from the start and when it does find the word "JAVA", there will be some values that is not equal to -1 that makes the if-statement satisfied and display the "J-A-V-A formed!".

Thank you for explaining it to me very well, I learned a lot from you.

Well, for informational purposes, using the last value of temp (JAVECJAVA), the method indexOf("JAVA") would return 5 I believe. Because that is the index of the start of the word JAVA in JAVECJAVA.

Indexes of Strings are one the most important thing to learn. It took me a while to figure out how string indexing worked so here is how I figured it out.

For this, think of the first row as the String and the second row and the indexes indicating the spaces between the letters (sorry about spacing, couldnt get the forum to post multiple spaces correctly).

. J A V E C J A V A
0 1 2 3 4 5 6 7 8 9

So if you called String.substring(3,6), which returns the string of the indexes between the selected ranges, you would get ECJ. And if we called String.substring(5,9) (or String.substring(5) if you want from the index to the end) you would receive JAVA.

Understanding the substring method and the indexing of strings is vital to understanding how to scan through a string or to cut off parts of strings.