A person's social security number is in a specific format with numbers and dashes:

nnn-nn-nnnn

For example, this is an example of a valid social security number:

111-22-3333

Note that this number is fictitious for this article.

To verify that a social security number is valid, follow these rules:

• The social security number must be a string.
• The string must be of length 11.
• Starting with position 0, there are hyphen (-) characters in the 3rd and 6th positions.
• All other characters in the string must be digits in the range 0 to 9.

Here are some sample social security numbers that fail to meet these requirements:

• 111223333 - length is not 11 and hyphens are missing
• 11-1223-333 - hyphens are in the wrong positions
• 111-aa-3333 - non-numeric characters are in positions 4 and 5
• 111-22-333 - length is not 11

Here is one possible algorithm to verify the format of a social security number:

1. Input the social security number as a string value.
2. Check the length of the social security number.
   • If the length is not equal to 11, output a message that the social security number is invalid and exit the program.
   • Otherwise, continue to the next step.
3. Check that positions 3 and 6 of the social security number are hyphen (-) characters. One way to do this is with the Java String charAt() method.
   • If one or both of the positions is not the hyphen (-) character, output a message that the social security number is invalid and exit the program.
   • Otherwise, continue to the next step.
4. Check that all other positions in the string are numbers in the range 0 - 9. One way to do this is with the Java String method isDigit().
   • If at least one of these characters is not a digit, output a message that the social security number is invalid and exit the program.
   • Otherwise, output a message that the social security number is valid.

This just one possible algorithm for verifying the format of a social security number. There are other ways to do this. But algorithm development is the focus here. Develop a solid algorithm before writing code. Then it is just a matter of translating the algorithm into real Java statements.

Thanks for reading. 😃

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