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How do I put the same hashmap with different values for each loop to my Hashmap<String, Hashmap>

 
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I am creating a student database that
- Lets user create new student records
- Lets user find a student record by their student ID
- if the student is found, output their details
This is the code I made:

After the first loop, if I choose to create a new student record it will to start to overwrite the previous one and I get two hashmaps with the same values inside my Hashmap<String, Hashmap<String, String>>:  

How do I create new values for the same hashmap without overwriting the previous inputted hashmaps? I am not supposed any methods, classes or anything object related.
 
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Welcome to the Ranch and enjoy the stay.

Well, think about the design first. What I'd expect perhaps as a user of your API is something like this:

where

When you create Student class, read about equals() and hashCode() and when they are needed and decide whether you need to override those methods in your Student class.

This is one way of structuring your system.
 
Jaredson Fetiza
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Liutauras Vilda wrote:Welcome to the Ranch and enjoy the stay. -Thanks


We have not really covered classes,methods or objects yet. Our professor evaluates us based on how we use what was taught in class.
 
Liutauras Vilda
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Jaredson Fetiza wrote:We have not really covered classes,methods or objects yet. Our professor evaluates us based on how we use what was taught in class.


I see. Ok then. Please start by letting us know, what tools do we have at hand?

Jaredson Fetiza wrote:I am not supposed any methods, classes or anything object related


That might be very tricky or even impossible.
 
Jaredson Fetiza
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We just covered:
- Arrays
- Arraylists
- For each loop
- Multidimensional Arrays
- Arraylist
- Hashset
- Hashmap

Are there no hashmap methods I can use to somehow do I want after line 24?
 
Jaredson Fetiza
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This is the instructions for the task if it helps.
Create a student database program that stores student records, which consist of:

Student ID
Full name
Age
Gender
Course
Year enrolled
The user will be asked whether they will enter a new student record or to search for a student record.

If they will search for a student then ask them for the student ID. If the student ID is found output the details of the student, if not then output not found.

If they will enter a new student record then allow the user to enter the students new details.

The program must also keep looping until the user inputs "quit".
 
Liutauras Vilda
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Well, if you can't create any custom classes like Student, but you can use Map data structure, then ok, your approach may work having:


Jaredson Fetiza wrote:How do I create new values for the same hashmap without overwriting the previous inputted hashmaps?


Overriding happens when you have the key you are about to add already added to a map.

For instance
 
Jaredson Fetiza
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Overriding happens when you have the key you are about to add already added to a map.

For instance



Yeah but I cant create new keys and value with my approach (not that I know of) because it is a loop using the same hashmap. I am experimenting with the hashmaps methods rn like
clone(), keyset(), clear() or values to somehow see if I can get around that.
 
Liutauras Vilda
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Jaredson Fetiza wrote:Yeah but I cant create new keys and value with my approach (not that I know of) because it is a loop using the same hashmap.


Why? Could you give an example please.

Jaredson Fetiza wrote:I am experimenting with the hashmaps methods rn like clone(), keyset(), clear() or values to somehow see if I can get around that.


I don't think you need any of those yet.
 
Jaredson Fetiza
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Liutauras Vilda wrote:Why? Could you give an example please.


Because I need to create a new one each time it loops?
- like this

Am I doing it right? What did you have in mind?
Honestly I am willing to start over from scratch cause I feel like it shouldn't be this complicated and there is a simpler approach of doing this haha
 
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Jaredson Fetiza wrote:. . . We have not really covered classes,methods or objects yet. . . .

What sort of course is this?
 
Jaredson Fetiza
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Campbell Ritchie wrote:What sort of course is this?


Computer Science?
 
Liutauras Vilda
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Jaredson Fetiza wrote:

Liutauras Vilda wrote:Why? Could you give an example please.


Because I need to create a new one each time it loops?
- like this

Am I doing it right? What did you have in mind?
Honestly I am willing to start over from scratch cause I feel like it shouldn't be this complicated and there is a simpler approach of doing this haha


So what I was thinking of (and that is purely to work on the structure you laid down with Map<String, Map<String, String>>):

But again, I'm not entirely sure what you can use in your assignment. It doesn't say that you are not allowed something, nor it does say what you are allowed. Only you said you are not allowed that and that. So I'm not sure.
 
Campbell Ritchie
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Jaredson Fetiza wrote:. . . Computer Science?

What you said makes me wonder whether you been taught any object‑oriented programming. I presume you have attended all the teaching.
 
Jaredson Fetiza
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Liutauras Vilda wrote:
So what I was thinking of (and that is purely to work on the structure you laid down with Map<String, Map<String, String>>):

But again, I'm not entirely sure what you can use in your assignment. It doesn't say that you are not allowed something, nor it does say what you are allowed. Only you said you are not allowed that and that. So I'm not sure.



Wait I don't get it. Isn't this what I am trying to do? Except that the main problem is I cant do what's in your comment.
 
Campbell Ritchie
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Liutauras Vilda wrote:. . . Overriding . . .

There are several meaning for the word “overriding”. It is commonly used about methods in object‑oriented programming, but Liutauras is using it differently. If you look in the Java™ Tutorials, you will see it says a Map “models the mathematical function abstraction”. Your map constitutes a function where x ↦ y and you are overriding a mapping in the function so that x ↦ z.
 
Liutauras Vilda
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Jaredson Fetiza wrote:Wait I don't get it. Isn't this what I am trying to do? Except that the main problem is I cant do what's in your comment.


I have 2 Maps defined.
You have 2 Maps defined.

One of my Maps is defined outside loop, another Map inside the loop.
How about yours?
 
Campbell Ritchie
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Jaredson Fetiza wrote:. . . Isn't this what I am trying to do? . . .

I think the above is dreadful design, but it should work. Lines 7‑12 create a Map as an anonymous class; the calls to put(...); should populate the map with all the data you require, so use as many put(); calls, or as few, as you need.
The types in lines 4, 5, and 7 can (should?) all be replaced by var.
 
Jaredson Fetiza
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I see so I cant use the same key because it can only contain one value. I thought I was creating a new key with the same name. If I need to create new keys each it loops,is it even possible to loop student record creation using hashmap?
I will try to start from scratch and think of something.
 
Campbell Ritchie
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You can use the same key as often as you like, but you will overwrite the value and thereby change the pair and change the function. If you have multiple mappings, you use a different key for each pair. Then each put() call changes the function by making it larger (=enlarging its domain) rather than altering a pair.
Remember that in a function, x ↦ y means that every time you put x into the function, you get y, never a, b, c, or z.
 
Campbell Ritchie
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Half an hour ago, I wrote:You can use the same key as often as you like . . .

If you use the same value repeatedly, you will have every key pointing to that value. Adding pairs to it will change  the state of the value, but not which object corresponds to y above.
 
Liutauras Vilda
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Campbell Ritchie wrote:overwrite


Thank you for correcting me. I wasn't precise earlier when I was choosing words.
 
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Jaredson Fetiza wrote:This is the instructions for the task if it helps.
Create a student database program that stores student records, which consist of:
Student ID
Full name
Age
Gender
Course
Year enrolled


This is EXACTLY the way the design for a Student object would be specified. Any other way to deal with that would be tortuous and send me off into the woods screaming. I'm sorry, but with wording like this in the instructions I believe they are telling you to create a Student object.
 
Campbell Ritchie
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Carey Brown wrote:. . . a Student object . . . Any other way . . . would . .  send me off into the woods screaming. . . . they are telling you to create a Student object.

Or they would if they actually taught tobject‑oriented programming. I had the good fortune to be taught by somebody (Elizabeth Norvall) who actually taught object‑orientation.
 
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