Map and HashMap in Java - Full Tutorial

Maps and HashMaps in Java can be so confusing when you're first starting out your Java career.

But Maps and HashMaps don't have to be confusing at all! A Map is a simple, powerful tool to have in your programming arsenal, and this video will give you everything you need to know to use Map and HashMap confidently in Java, even if you're a Java beginner.

Learn or improve your Java by watching it being coded live!

Hi, I'm John! I'm a Lead Java Software Engineer and I've been in the programming industry for more than a decade. I love sharing what I've learned over the years in a way that's understandable for all levels of Java learners.

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[gur]

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[yuto]

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[youthought]

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[BernardVisagie]

2:28, now in C# you can infer even more, and you would be able to write your Java as: HashMap<String, Integer> empIds = new();

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[carriewright]

Thank you so much John! Your videos are great! I love how I can learn what I need in just 10 minutes as opposed to the typical school setups we have all experienced in other venues that takes hours and leave you confused.

[JacobLoneWolfin]

I took notes to make myself a cheat sheet from this and work on my typing speed. Love these videos!

HashMap <Key Type, Value Type> name = new HashMap<>();



name.put([key object or value], [Value or object]);

adds a Key and a Value to the hashmap





System.out.println(name);

[Outputs:

"{Key=Value ....}"





[Outputs: Value associated with Key]





Prints Boolean answer to inquiry -- does the "key" exist in the map? True.



Prints whether or not map contains "value"

Put overrides previous calls to put method on the same key

hashMapName.replace("key", Value);

will replace entry for key, but does not create new entries

HashMapName.putIfAbsent(key, value);

adds the key and value to map, if absent

[flytoinfinityvivi]

This video literally equals to an hour of studying trying to understand Map. You are amazing! Please never stop what you are doing. You actually make us beginners understand and well hopefully making us the future IT people (:

[aryanjoshi]

in ten minutes i am able to learn which others explain in double or triple amount of time and comprehended 95% of the video content, thanks to your explanation, thank you john sir

[zlyglco]

Hey John.

I've been watching your videos for the last few hours and so very glad I found you.
I'd been struggling with making LinkedLists and HashMaps make sense in my head and your explanations + examples struck a note with me.

Thanks a lot.

[mattmalan]

Thank you so much! I've got this massive project due in a few days!

[crookedcrowe]

I have a test coming up tomorrow and this guy is literally saving my life by making things simple and clear to understand. THANK

[ReallyAqua]

Why do you not have a lot more subscribers? You have helped me so much and you deserve to have a lot more. Thanks for helping me out on so many things!