Character at function in java

String method in Java: charAt()

I have an assignment that I’m finding a bit difficult. We’re reading an external file to get the numbers needed for the program, which is not a problem. Here is the prompt: To check the validity of the code you need to analyze each digit in the code including the check digit. Assume that the first digit is in position zero, add the digits in the even positions and multiply the result by 3. Add this to the sum of the odd positioned digits. Only if the total is a multiple of 10 is the UPC number valid. Write a program that reads a UPC code (as a string) from an external file, analyze the code, and output the code and a label “Invalid” or “Valid”. Sample Output: UPC Code: 016499215511 Valid 372415613274 Invalid 155512994610 Valid 011165459192 Invalid 838241762110 Invalid Here is what I have in my code so far:

import java.io.*; import java.util.*; public class Prog700d < public static void main(String[] args) throws IOException < Scanner kbReader = new Scanner(new File("C:\\Users\\Guest\\Documents\\java programs\\Prog700d\\Prog700d.in")); while(kbReader.hasNextLine()) < String upc = kbReader.nextLine(); int length = upc.length(); int a = upc.charAt(0); System.out.println(a); 

My main issue is with the charAt(). I think that if I use charAt(), then I will get the character at the given index. So I decided to test this by using charAt(0), and I ended up getting these numbers: 49 55 53 49 51 I am really confused on how I got these numbers, and honestly have no idea what went wrong. I can do the rest of the program (such as the formula, printing out everything, etc.), but I don't know how to fix the charAt() problem. I know I can handle the rest of the assignment, but I have no idea what went wrong with this. If someone could provide some guidance on how to fix issue, it would be greatly appreciated. Thank you!

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charAt() in Java – How to Use the Java charAt() Method

Ihechikara Vincent Abba

The charAt() method in Java returns the char value of a character in a string at a given or specified index.

In this article, we'll see how to use the charAt() method starting with it's syntax and then through a few examples/use cases.

How to Use the Java charAt() Method

Here is what the syntax for the charAt() method looks like:

public char charAt(int index)

Note that the characters returned from a string using the charAt() method have a char data type. We'll see how this affects concatenation of the returned values later in the article.

Now let's see some examples.

In the code above, our string – stored in a variable called greetings – says "Hello World". We used the charAt() method to get the character at index 0 which is H.

The first character will always have an index of 0, the second an index of 1, and so on. The space between substrings also counts as an index.

In the next example, we'll see what happens when we try to concatenate the different characters returned. Concatenation means joining two or more values together (in most cases, this term is used for joining characters or substrings in a string).

Using the charAt() method, we got the characters at index 0, 4, 9 and 10 which are H, o, l and d, respectively.

We then tried to print and concatenate these characters: System.out.println(ch1 + ch2 + ch3 + ch4); .

But instead of getting "Hold" returned to us, we got 391. This happened because the returned values are no longer strings but have a data type of char . So when we concatenate them, the interpreter adds their ASCII value instead.

H has an ASCII value of 72, o has a value of 111, l has a value of 108, and d has a value of 100. When we add them together, we get 391 which was returned in the last example.

StringIndexOutOfBoundsException Error

When we pass in an index number that exceeds the number of characters in our string, we'd get the StringIndexOutOfBoundsException error in the console.

This error also applies to using negative indexing which is not supported in Java. In programming languages like Python that have support for negative indexing, passing in -1 will give you the last character or value in a data set, similar to how 0 always returns the first character.

In the code above, we passed in an index of 20: char ch1 = greetings.charAt(20); which exceeds the number of characters in our greetings variable – so we got an error thrown at us. You can see the error message commented out in the code block above.

Similarly, if we pass in a negative value like this: char ch1 = greetings.charAt(-1); , we would get a similar error.

Conclusion

In this article, we learned how to use the charAt() method in Java. We saw how to return characters in a string based on their index number and what happens when we concatenate these characters.

Lastly, we talked about some of the instances where we would get an error response while using the charAt() method in Java.

Источник

Java String charAt() Method

The method charAt() in Java can be defined as the inbuilt method that returns the character value at the stated index number when searched in a string.

Syntax of charAt() in Java

The syntax of the charAt() in Java is as follow:

where string can be described as an object belonging to the String class.

Parameter of charAt() in Java

The charAt() method in Java has the parameter as an index.

index: The index is defined as the place of the character present in a string as its integer value.

Return Value of charAt() in Java

Return Type : Character

The character present at the specified index is returned.

Java String charAt() Method Example

Let us understand one basic example to explain the method charAt() in Java.

Explanation: As can be seen above we have printed the first and nineteenth characters from the string which says "Learning Java" . Here is the total length of the character in the string is 12 and we have printed the 1st and 8th characters.

Exceptions of charAt() in Java

IndexOutOfBoundsException : Thrown when the index provided is negative or greater than or equal to the length of the string.

What is charAt() in Java?

We can define the charAt() function in Java as the method by which we can return the character value for a particular index number belonging to a string while executing the charAt() method.

As we know while counting the index numbers in Java we start with 0 for specifying the first character, 1 for the second character, and so on.

This index value can be defined to be between 0 and (length of string - 1).

More Examples

Example 1: Java String charAt() Method

Let us understand the charAt() Method by the below example.

Explanation:

Here we are using the charAt() in Java to print the first, ninth, and twelfth characters of the string. As can be seen we used the charAt() in Java and specified the index 0, 8, and 11 respectively as the index value starts from 0 not 1 in Java.

Example 2: Java String charAt - IndexOutOfBoundsException

Let us understand the charAt() Method to understand the IndexOutOfBoundsException by the below example.

Explanation:

Here we see that we get StringIndexOutOfBoundsException as the index that we gave was negative and as we already studied for any index which is negative of more than the range of the index for a string we will get this exception.

Example 3: Java String charAt - Print All Characters of the String

Let us understand the charAt() Method to print all characters of the string with the help of below example.

Explanation:

Here we see that for printing all the characters of a string we have used the logic of loops in Java. We used the for loop to print each index character from the index value ranging from 0 to lengthofstring()-1 . If we exceed that it will definitely give us of bound exception.

Example 4: Java String charAt - Printing the First and Last Character of a String

Let us understand the charAt() Method to print the first and last character of a string with the help of the below example.

Explanation:

Here we are using the charAt() method to print the first and last character of the string. As we already studied the index value in Java starts from 0 and not 1, we use the index value as 0 to print the first character and the length of string-1 to print the last character of the string.

Example 5: Java String charAt - Print Characters Presented at Odd Positions

Let us understand the charAt() Method to print the character present at the odd places of a string with the help of the below example.

Explanation:

Here we have used the for loop along with charAt() in Java to specify a condition of the index value to give output other than 0 which states that those are odd positions and then once we have those index values we then print the values of those characters from the string.

Try yourself by modifying the code to print the characters present on the even position.

Example 6: Java String charAt - Counting the Number of Vowels in a String

Let us understand the charAt() Method to Count Counting the Number of Vowels in a String with the help of the below example.

Explanation: Here we have made the use of charAt() in Java to count the number of vowels in a string.

Example 7: Java String charAt - Counting the Occurrence

Let us understand the charAt() Method to count the Occurrence of a character from a string with the help of the below example.

Explanation:

Here we have counted the occurrence of the character 'S' from the string. We have used the for loop with charAt() in Java to increase the counter value every time it sees the character 'S' and as shown in the code above we have counted the number of times the letter 'S' occurred in the string which in this case was 1.

Conclusion

• The method charAt() in Java can be defined as the inbuilt method that returns the character value at the stated index number when searched in a string.
• The syntax of the charAt() in java is as follow:

• The output for negative integer or out-of-bounds positive integer when passed while executing the charAt() in Java gives the StringIndexOutOfBoundsException exception.
• We have studied so many examples covering a variety of scenarios where we can make use of simple charAt() in Java and simplify our process.

Источник

Java String charAt() Method

The charAt() method returns the character at the specified index in a string.

The index of the first character is 0, the second character is 1, and so on.

Syntax

public char charAt(int index) 

Parameter Values

Technical Details

Returns:	A char value at the specified index of this string. The first char value is at index 0
Throws:	IndexOutOfBoundsException - if index is negative or not less than the length of the specified string

❮ String Methods

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