Assume HashMap and Map are imported from the java.util package. (a) Can a HashMa

Question

Assume HashMap and Map are imported from the java.util package.

(a) Can a HashMap<String,Number> be used in a context where a Map<String,Number> is needed? Give a convincing explanation as to why or why not.

(b) Can a HashMap<String,Number> be used in a context where a HashMap<String,Object> is needed? Give a convincing explanation as to why or why not.

(c) Can a HashMap<String,Number> be used in a context where a HashMap<String, ?> is needed? Give a convincing explanation as to why or why not.

(d) Can a HashMap<String,Number> be used in a context where a HashMap<?,?> is needed? Give a convincing explanation as to why or why not.

Explanation / Answer

[A] Yes , We can use it , because HashMap in child of Map interface.

[B] Yes , becasue Object is Super Class in java. So Number object Value Can be store in Object .

[C] ? is used as a wildcard which is used when providing a type argument, e.g. List<?> foo = ... means that foo refers to a list of some type, but we don't know what. So Yes

[D] Same Reason in C, So Yes

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