Question

I am new to java and have a question

myBooks = new ArrayList<HashMap<String,Object>>();

What is HashMap and what does it mean when we use < > for ArrayList class?

Answer 1

Both HashMap and ArrayList can be considered as array in PHP. ArrayList is indexed by number, and HashMap is collection of key value pairs – PHP does not differentiate those two situations.

This particular declaration says that there is an ArrayList (number indexed array) and all its element are of type HashMap. For each HashMap, which is a collection of key/value pairs, the keys are of type String, and values are of type Object.