Java initialization of a map embedded within another map

Question

Good afernoon:

I have recently created a certain class 'X' which contains a single attribute "network" which is defined as a map which uses a String as a key and another map for the value (double map). For this class, the "hashmap" implementation will be used.

The class looks approximately like this:

public class X { private Map<String, Map<String, Integer>> network; //Attribute public X() { network = new HashMap<>(); //An empty map is created } public int method1 { String string = "sentence"; int number = 2; String string2 = "another"; network.put(string, <string2, number>); //NOT WORKING - wrong syntax/wrong initialization? } }

However, as I execute the network.put instruction contained within the function, the compiler automatically detects an error: "Expression expected". If possible, I would like to know whether I'm using the wrong syntax when adding a new key-value element into the map or if it's the initialization of the map that's causing the error.

All help is greatly appreciated. Thank you.

Andy Turner · Accepted Answer · 2019-10-06 16:16:40Z

You need to do:

public class X { private Map<String, Map<String, Integer>> network; //Attribute public X() { network = new HashMap<>(); //An empty map is created } public int method1() { String string = "sentence"; int number = 2; String string2 = "another"; Map<String, Integer> map = new Hashmap<>(); map.put(string2, number); network.put(string, map) ; } }

The idea is to create and initialize a new HashMap. Then add the key and value pair to it. Finally insert the map into the enclosing map.

Thank you so much both of you for your answers, the problem is now fixed. Have a good one.

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