Hospital Client Lookup System (Java)

This project demonstrates how to use a HashMap in Java to store and retrieve client information based on a unique key. In this case, the unique key is the client's Social Security Number (SSN).

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What is a HashMap?

A HashMap is a part of Java’s Collections Framework and provides a way to store data in key-value pairs.

• Keys must be unique (in this project, the SSN is used as the key).
• Values are associated with keys (here, each SSN maps to a Client object).
• HashMap allows fast lookup, insertion, and deletion operations, typically in constant time, O(1).
• The HashMap library is a generic class that can be initialized using the generic interface Map.
• The generic parameters are HashMap<K,V> where K is a class representing the key and V is a class representing the value.
• This example will relate String to a Client (a record class).

HashMap Example

Map<String, Client> map = new HashMap<>();
map.put("123-45-6789", someClient);
Client result = map.get("123-45-6789");

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Project Overview

Client (record)

Represents a hospital client with the following fields:

• SSN
• First name and last name
• Birth date (month, day, year)
• List of comments

Includes:

• addComment(String comment): Adds a new comment to the client.
• toString(int indentLevel): Formats and returns the client's details with the specified indentation.
• toString(): A no-indentation version for convenience.

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ClientLookup

A helper class that:

• Stores clients in a HashMap<String, Client> using SSN as the key.
• Allows clients to be added (addClient) and retrieved (lookUpClient).

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Main

Demonstrates:

1. Creating multiple Client objects.
2. Adding comments to each client.
3. Storing them in the ClientLookup system.
4. Looking up clients by SSN and printing their details.

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Example Output

A Few Recent Clients:
	Client Information:
		SSN: 123-45-6789
		Name: Jane Smith
		Birth Date: 3/14/1985
		Comments:
			- Regular checkup.
			- Blood pressure is high but not a significantly.
			- Advised client to exercise more.

	Client Information:
		SSN: 987-65-4321
		Name: Mark Johnson
		Birth Date: 7/22/1978
		Comments:
			- Annual DOT physical completed.

	Client Information:
		SSN: 555-55-5555
		Name: Emily Davis
		Birth Date: 12/5/1992
		Comments:
			- Client fell asleep in lobby and missed appointment.
			- Follow-up visit next week.

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Notes

• Java record classes are immutable by default, but mutable fields like List can still be changed unless made unmodifiable.
• Using SSN as a key demonstrates how unique identifiers can be used for fast and precise lookups in a system.

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Package Structure

org.example
├── Main.java
└── hospital
    ├── Client.java
    └── ClientLookup.java

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How to Run

1. Compile all .java files:

   javac org/example/*.java org/example/hospital/*.java

2. Run the main program:

   java org.example.Main

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