A clarification on Java's Map system and ":" operator

June 14, 2022

I am trying to learn Java’s Map<> system.
I cannot find a lot of information about it online so I am referring myself to a website called javatpoint.com.

At one point in the explanation the code used looks like this:

public static void main(String args[]){  
  Map<Integer,String> map=new HashMap<Integer,String>();  
  map.put(100,"Amit");  
  map.put(101,"Vijay");  
  map.put(102,"Rahul");  
  //Elements can traverse in any order  
  for(Map.Entry m:map.entrySet()){  
   System.out.println(m.getKey()+" "+m.getValue());  
  }

I can understand most of it up until

for(Map.Entry m:map.entrySet()){  
   System.out.println(m.getKey()+" "+m.getValue());  
  }

I have absolutely no clue what is happening here, firstly, what is the ":" operator, and secondly what exactly does ".Entry" and ".entrySet" do?

I would really appreciate an explanation as I have a heavy background in python but have never seen this.
Thank you!

>Solution :

: is part of java foreach syntax:

for (type var : array) 
{ 
    statements using var;
}

Using foreach you are getting collection items one by one. map.entrySet() is your collection of items and Map.Entry m is a single item of collection that you get in each iteration of foreach.